I worked at a television station years back that was designed in such a way that the lights going up the tower were powered by the separate phases of three phase AC with the one at the top powered from all three combined. This was pretty normal but what the engineer had done was rotate them at every level so that if a phase was dropped you could count the lights and quickly see from a distance that the power wasn't right. 4 lights was good, 3 meant you dropped a phase, and so on. I thought it was a pretty clever way of keeping light on all sides of the tower while being able to tell from a distance that a phase was out.
This is best practice for anyone who uses three phase power.
A machine shop should connect 1/3 of their lights to each phase so it is immediately obvious if a phase gets dropped. Lots of equipment will suffer on two of three phases but with lower performance or even damage.
At work we run a lot of machinery with motors and its obvious when phase loss happens. From my office I can tell if the lights go out/dim and the usual shop "hum" becomes a buzzing grunt that is immediately identifiable. Older machines have to be manually powered down but the machines I rebuilt have phase loss protection in the PLC thanks to a power monitoring terminal in the IO (Beckhoff EL3453.) Since the PLC is on 24V DC I have a capacitor backup module fronted by a 24V PSU that takes the 480V three phase power which tolerates a phase loss. The machine safely stops the process and shuts down the pumps and any other AC loads, then waits to be manually powered off as the PSU and DC side doesn't care.
I was told that you want lights on all 3 phases so that you can see spinning things spin. If the lights are on single phase, they will dim 120 times a second, and the strobe effect can cause spinning things to appear stationary. With 3 phase, at least 1/3 of the lights are lit all the time.
That's a valid reason too. In an industrial environment full of rotating machines, thinking something is stationary because it's on the grid's natural frequency can be lethal.
It's way less of a problem with modern machinery, and leds will blink in uncorrelated phases in a frequency that is different from the grid's anyway.
For residential lighting running off a single-phase supply, there are some annoying LED bulbs with simple half-wave rectification that strobe at the grid frequency with less than a 50% duty cycle (often seen with bulbs emulating vintage exposed-filament bulbs with no frosted glass). It would be interesting to see how much less annoying that kind of flicker is when you have a three-phase supply to a light fixture, so that at least one set of LEDs was illuminated at all times.
There are no light fixtures that use three-phase power. At least that’s my belief, as I’ve never heard of one or seen one and I’ve been working in the electrical industry for almost a decade. You could theoretically arrange three lampholders like a delta or wye transformer [0] and connect a phase to each one and all three lamps will be lit, but the lampholders will be energized, so make sure to wear voltage-rated gloves when changing out the lamps ;) This is how three-phase resistive heaters are wired, the drop in ampacity and large resistive heating loads make it worth using three phase since ampacity is 1.73 times lower than it would be on a three-phase circuit than it would be at the same voltage as a single-phase circuit.
In the US, there are 208V single-phase and 480V single-phase lights that use two of the three phases. In practice, indoor lighting is either 277V (line to neutral on a 480V service) or 120V (line to neutral on a 208V service). Most commercial LED fixtures can use any voltage between 120V to 277V single-phase.
480V single phase is used for some pole lighting with long runs of conductors to handle voltage drop. Anything over 277V has to be elevated at least 22 feet off the ground per the NEC.
Back in the analog TV days, I could see the flicker on the 50hz PAL/SECAM signals whenever I visited Europe, especially when the screen was white and in my peripheral vision. I always wondered why it didn't drive everybody nuts, but then I got used to it. I did always wonder if there was a way they could have eliminated that (maybe they did in more expensive TVs that fired off at double the reference signal and not in cheap TVs in hotels/bars?).
simple answer is grid frequency in europe is 50hz, in the US and Canada it's 60hz.
Early TV's synchronised to the grid frequency (and drew the entire screen on each cycle) - also remember TV's where analogue to start with (and operated at large voltages/transformers) so if they didn't sync with the grid electrical noise becomes a big problem with the power supply.
The 100 Hz TVs weren’t that common and had other issues. They weren’t strictly superior. TVs were supposed to use a different set of phosphors for 50 Hz that were less flickery at 60 Hz but in practice I don’t know if tube producers bothered to have different sets for the different markets.
Are/were there 3-phase fluorescent tubes available?
Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously? Without such malarcky as shadows or inverse-square to muddy our vision?
Or maybe a multiplicity of single fixtures with 3 tubes -- one tube per each phase?
And even then: Doesn't it still strobe somewhat at (50*3*2)=300 or (60*3*2)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
(LEDs are out-of-scope of this question, of course: Line-voltage LED lamps can have integrated electronics and can therefore have diode elements that are driven by things that approach [or even achieve] DC, which changes the rules.
And, of course: Incandescent lamps have enough persistence that stroboscopic effects are generally not an issue with a human eye.)
You typically connect 1/3 of lamps on one phase, one third on another and so on.
In the UK we use a 230V single phase system for most things (industrial/commercial often use 400V) (if all three phases are in use it's 400V - you may see it as 415V but we harmonised with Europe to 400V) so lighting expects that 230V anyway, you still have a common ground, you just run the live for each phase to the lamp/light.
Power delivery to homes is in effect a single phase out of a three phase supply with each house (often but not always) wired in sequence, so house 1 is Phase 1, house 2 is Phase 2, house 3 is Phase 3, house 4 is phase 1 and repeat.
We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
> We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
Never even thought about the fact that different regions may have different colour standards. This explains some of the power cables I've torn apart over the years and the strange colours I found inside!
> When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
Making a mental note of that one... a black neutral would be a nasty surprise coming from North America.
Indeed, half my house is blue/brown, the other half is black/red since reg changes where grandfathered in and the wiring has been added to (some places clearly by a knowledgeable individual others..not so much).
I spent the first day after we bought it and moved in going around with a screw driver, side cutters a notepad and enough swearing to make a pirate with Tourette’s blush.
It’ll need a full rewire at some point, while I can do it myself to a commercial standard our regs require a currently qualified electrician sign off (mine expired many years ago) so I’ll just pay someone to do the lot.
It’s annoying but I’ve seen enough horror shows to see why it’s nescessary.
> Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously?
That's exactly what they mean, yes. Some lights on L1, some L2, some L3.
> And even then: Doesn't it still strobe somewhat at (5032)=300 or (6032)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
No, because the phases are overlapping, there is no point in time where they're all off. There'd be local dimming of course, depending on their position etc., but light for all of the second.
They're saying that you have 3 banks of lights, each connected to one phase of the 3 phase input. That way, when only 1 bank goes out, it's easy to see that one phase is out.
> This is best practice for anyone who uses three phase power.
No, it’s not. It’s a neat trick that visually reveals when the utility drops a phase, but there are better ways to handle avoiding equipment damage.
Best practice is to use phase monitoring relays that can de-energize a motor when a phase is dropped/reversed to prevent damage. The trip time is adjustable and it’s more reliable than manually hitting an e-stop. It also won’t let a motor with incorrect phasing start up either. You see phase loss relays on a lot of compressor motors and other large motors.
Clever! I know I talked to the folks at Masterclock in St. Louis recently about one of their clock displays; they intentionally default the separators to flash if the clock is not synced to NTP, and then they go solid once the connection is established.
It's a quick way to know if something is down, using context clues that are already there to begin with!
> Joe: [...] So whenever there's a project on the tower, it's not unusual to see the guys in some kind of a, what do they call those?
> Jeff: A full ghillie suit? Or I don't know what they're called.
If you see someone up in a tall tower wearing a ghillie suit [0]... that sounds like time to call emergency services while avoiding their line-of-sight. :p
Haha, yes. For some reason, ghillie suit was the only thing I could think of at the time. I think they wear basic tyvek suits while doing paint work, not sure if they need full hazmat (maybe if the tower has lead paint?).
> Tower painting has changed a lot over the years. The older towers have lead in them. So whenever there's a project on the tower, it's not unusual to see the guys in some kind of a, what do they call those?
> If you see someone up in a tall tower wearing a ghillie suit
My first thought would be “that might be the dumbest sniper I have ever seen”…while I was taking cover, because even if they are dumb, they might still be a capable marksman.
I imagine that a properly constructed ghillie suit covered with chain link fencing, barbed wire, no trespassing signs and a blinking red light might go undetected...
One interesting fact I learned in a different discussion is that when LED lights are used for obstruction lighting, the FAA has standards that require infrared emitters to make them visible to night vision goggles, since unlike incandescent bulbs, some LED's can be invisible to NVG's.
tl;dr NVGs are sensitive to near IR so you want lights that are dim in those wavelengths (but not completely out since you still want to see them with NVGs) while still being bright in visible light. There's a neat picture of the flying controll tower on one of the UK's Queen Elizabeth-class aircraft carriers that shows two rooms with similar illumination levels in visible light, but under NVGs one room which isn't NVG compatible is massively brighter than the other. In the NVG-compatible room there were still a handful of panel indicator lights that were not compatible and lit up the whole space
These beacons are also great for navigation. Aeronautical charts usually show the color/pattern of the light. You can use those as points to triangulate your position.
You have brought back to me memories from 30+ years ago, playing Microsoft flight simulator, trying to triangulate my position using VOR beacons as quickly as possible before my aircraft had moved so far on that I was no longer anywhere near my triangulated position, hah!
I never appreciated how realistic FS was until I started studying for the navigation part of my PPL. I flew a 172 too so the instruments felt very similar.
Lighthouses are usually white. They used to rotate (sweeping the beam) but tend to flash now I think. Nautical charts show the elevation of the light, the visibility ranges and the pattern of on/off (eg Fl (2) 10s 41m 17NM). Some lights are sector lights, so red/white/green depending on your position, they indicate if you are in the correct approach channel.
It can be really confusing approaching a port at night. Never mind the city lights behind, and the cars driving about. 20+ lights flashing at different rates in the dark, some of them disappearing for seconds at a time. Oh, and if you turn your light on to refer to the chart, there goes your night vision!
Boat masts above 25m also have blinking red lights for the low flying aircraft (I guess its a bragging point)
Slightly off topic: typically, lights of neighboring towers blink asynchronously. But sometimes they are synchronized. Very satisfying. Anyone knows how this works? My best guess is e.g. DCF77. Thoughts?
I believe it's usually GPS/GNS (they all receive the time via GPS independently, and flash at predetermined times). The FAA requires synchronization for many classes of obstruction because it makes it clear that you're looking at obstruction lights rather than e.g. brake lights or traffic lights on the ground.
Could they also use power grid sync? Not sure as I haven't talked to anyone in wind power, but grid sync would be pretty close to 1 Hz at least in the US.
Building a product that would sync at 1 Hz via GPS that works in the US and other countries with 50 Hz power would be a little easier than syncing to grid phase though.
You can have each tower derive a perfectly stable 1Hz signal from the mains, but you have no way to synchronize those signals. Each tower's 'tick' starts at a random point in the 60Hz cycle.
You need an external, dedicated channel for this. You either synchronize with signals sent between towers or with a global signal from somewhere else (space). GPS broadcasts atomic time references for free, so everyone just uses that
Definitely GPS. Other methods have been used in the past--I remember reading operating reports from a wind farm nearly 20 years ago that slowly brought all its lights in line with each other over several months--but these days you can buy mainstream lighting with the GNSS receiver built in from a number of suppliers. They make it easy.
For wind farm use most also have an external input for ADLS triggers, though that usually also requires a separate controller and communications connection to manage the ADLS signals.
The flashing red lights are L-864 type. The requirements are 20 to 40 flashes per minute (FPM), and typically 30 FPM is used.
You'd probably have better timekeeping from a reasonably connected Pi with a common NTP daemon (take your pick, some are easier to configure / query), and a realtime-ish thread to emit your PPS signal on a GPIO or similar.
Probably more robust than line of sight, and able to pool with other NTP servers in your home-lab (and beyond).
My observation is not that they are sometimes synchronised, but some subset of the towers are synchronised (this was my observation in Melbourne AU). Upon asking reddit, it appears that it is the FAA-preferred option that all lights are synchronised:
https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
If you look close - almost impossible in the dark - you will see that most wind turbines don't have any lights at all. Too many lights is a distracion but all the synchronized lights are an easy to understand 'stay away from this whole area'.
Driving through a massive wind farm at night is a trip since they all blink in unison. Having them all independently would look interesting but could rapidly descend into madness:
Yeah, I've seen it with windfarms. Always wondered why do they need to blink at the same time. The scale of the blink is pretty jarring at night (but also awe-some, in the same way any big enough infrastructure project inspires a kind of awe).
Wind farms have a certain amount of nimbyism because they "spoil the natural landscape." (So do regular farms -- nothing natural about grain silos or row crops, but that's a side topic...) Anyways, having that many towers blink in unison across that big a landscape is a weird effect when you first see it. I think there's an argument that if they blinked independently it would feel more natural in a way.
But since the blinking is all FAA requirements, I assume it's to help identify all the individual towers from the air. I suppose if they were all blinking independently, it would be a predator-trying-to-focus-on-a-single-zebra-in-the-herd problem, except in this case the predator is a pilot trying not to crash into a turbine.
Sure would emit more subtle 'part of the landscape' vibes though.
(Which I guess is exactly what you don't want when you're flying above them. Sigh.)
It's so pilots see the entire wind farm as a single entity and can interpret what they see and understand the extent of the wind farm easily. There is a pretty good study you can read on this:
As to community impact, radar-activated lighting is an approach that is being used in places this is a concern. It allows the lights to remain off unless there is a plane within the envelope that requires the lights to activate. It's expensive though.
This is a safety measure. You can't rely on ALL aircraft having functional (or installed) transponders. You must actively sense incoming craft because they don't always politely announce themselves.
At small unattended airfields, you can sometimes turn on the field lights by transmitting on a particular frequency (as if you were calling the non-existent tower in quick succession).
If they don't sync to a common clock source, they won't stay in sync for long. Probably not even for a few minutes or so.
You'd get the same phenomenon that you see when operating turn signals in traffic. They seem to weave "in and out" of sync. The frequency at which that happens is the beat frequency, i.e. the difference between the two blinking frequencies.
It's a bit larger than a 555, but it should keep you within a small handful of microseconds per day until the aging effects start to add up which make getting more than a millisecond a year dicey, even if the thing doesn't die on you: https://www.ipgp.fr/~crawford/2017_EuroOBS_workshop/Resource...
A cheapo 20ppm quartz watch crystal definitely doesn't drift by a second every few minutes, but it will over about about half a day at maximum error. A 5ppm one (still sub one Euro) will keep a second about every two days. A 0.5ppm TCXO can be had for about 15 Euros from Mouser and that gets you two weeks.
If you have shared line power you can just use that and everything will be locked in sync forever.
If you don't want to use that or radio, and you are outside, you could try to be really clever am sync your flash phases to a specific position of the sun. This is what the Long Now clock does. It'll be a different time each day, but it'll be the same for all units, within a small tolerance.
Well, yeah. I was sort of assuming that you won't use a TCXO or even just a cheapo quartz crystal, because it doesn't make a lot of sense: You've now thrown money at something that will relatively quickly desync anyway.
I mean, sure, the TCXO will mean that you only start seeing a phase difference between the two after weeks instead of minutes, but what's the point of that? I you want them to be at the same phase, you'll need to sync them at some point, and you do that by using a common clock source.
So either you shell out some effort for a real solution (power line is nice, and also qualifies as a common clock source as I've predicated), or you don't. And if you don't, there's no point in using a precise-ish clock at all, and you'll likely end up with very quick desyncing.
Wouldn't the mains frequency be a common clock source, if nothing else?
But presumably these lights at least have battery backup, given the obvious risks in case all of them were to fail at the same time due to a grid issue.
Yeah, the mains frequency qualifies, if you explicitly use that.
(Doesn't solve the problem if you want them to be in sync phase-wise, i.e. blink at the same time or similar, but at least they won't drift apart, which was what this is about.)
You could still sync with that signal because it's not perfect.
For example, say you have a scheme where a period longer than the last one is symbol A, about the same period is B and shorter is C. You will get a random-ish sequence of symbols.
If you have an algorithm that, say, resets the timer to zero whenever a certain symbol sequence is detected, you can eventually get back in sync. With some care you can make sure you only sync when the sequence happens and the light has only been off for a short period to avoid excessively long off periods or truncated on periods.
Then you just need to have a local oscillator good enough to do that timing analysis and that can maintain sync between these symbol occurrences.
You could do it on the tiniest micro. Once you've counted the zero crossing detector, these days you might save 3 to 5 whole dollars over a GPS receiver on your very expensive ICAO compliant lamp and also ruled out using DC into the bargain! And theoretically it desyncs when the grid is too stable for days on end (and you just get BBBBB or ABABAB for millions of cycles)!
In terms of what is actually used, they do often use GPS and many of them have MODBUS or similar data connections which presumably wire into the wind turbine's telemetry somehow for fault detection.
It is entirely self-contained (but needs zsh, not bash, for dumb reasons). Terminal at 90 columns works best.
It is just a very simple integer LFSR as a random number source, followed by a hand-made integer IIR filter (manually placing poles on the z-plane). All of this entirely with trivial integer operations only (effectively using 32 bit fixed point arithmetic)
So without any external input or tools at all, and not even using zsh's $RANDOM, it makes an "analog" weavy pattern.
Which is not obvious at all if you have JavaScript disabled by default, since it only shows up as a blank space, which could also be a blocked ad or an image which failed to load correctly.
The first few times I saw one of these transcripts with video at the top (IIRC, it was on Practical Engineering, not this site), I thought it sounded odd but didn't get that it was a transcript. Only later did I find out that there were videos (and they're great).
In the past year or two they have also added a quick periodic flash of white light for when visibility is low; like a camera flash that happens every few seconds. I think it was added this spring but don't quite remember.
Related: Some wind turbines apparently only turn on their position lights when there's any aviation traffic nearby (as detected by either local transponder interrogators (possibly ADS-B receivers?) or radar)!
Radar, called Aircraft Detection Lighting Systems (ADLS). The requirements are summarized in the FAA Advisory Circular covering aviation marking and lighting.
In Norway this is regulated by Luftfartstilsynets BSL E 2-1, and the blinking white lights on our towers are called "hinderlys", for example category "Høyintensitet, type B".
They are not uncommon in Norway.
If you go to one of our major airports you will see one on the tower. The blinking lights also sit on wind turbines and TV masts, and anything taller than 15 meters in rural areas or 30 meters in populated areas will have some kind of light on it, sometimes blinking, either red or white.
Strictly speaking they should be unnecessary because there are published minimum safe altitudes for every air space over land. But some aircraft must be able to “See and avoid”
the towers in my area all switched to LED recently. the slow, glowing blink of the incandescent ones probably isn't as visible as the modern ones, but I do dearly miss seeing it out my window.
Blinking attracts attention which is the real purpose. I'd assume based on how we detect motion more easily, these add a bit of "motion" to attract our attention
I know. But when I was programming LEDs for my single board computer, I found that blinking the LEDs used a lot less power. If the blink rate was fast enough, your eye did not distinguish that from the LED being on 100% of the time.
I don't know if battery powered devices generally use that trick or not.
all dimmable LEDs use blinking, but interesting case for your suggestion for an even more efficient use of a "steady" LED. what blink frequency did you use to keep it from being visible to the eye? did it not dim the overall brightness to a meter? early LEDs were atrocious with their slow blink rates that quickly scanning across them could see it, but even more noticeable if you pointed your camera at them. now, they blink incredibly fast, fast enough even for some slo-mo to not strobe.
You only need about 40hz to make it seem on all the time, TVs (before 2020, maybe earlier) only did 25hz-ish. You can actually play pretty ridiculous tricks on the brain if you know this. For example, in VR, in a large enough room, you can slightly alter the angle the player sees inbetween frames. This alteration makes the brain think youre slightly offset from where it thinks you should actually be. This allows you to cause a person to walk in a circle irl, while they think they are walking in a straight line. Unfortunately only works up to a threshold of change, before the brain starts getting confused and causss the user motion sickness.
Fwiw, these "tricks" are nice for some, but cause headaches for those who're PWM sensitive (like me). I can easily see the flicker of eg my Pixel 5 screen (which iirc is around 300ish hz?), and it hurts my eyes.
Fortunately, some folks like Philips make bulbs that are very low or zero flicker.
>TVs (before 2020, maybe earlier) only did 25hz-ish
tell me your European without telling me.
> You can actually play pretty ridiculous tricks on the brain if you know this.
I do random persistence of vision tricks all the time. I can see flickering in cheap CFLs or old tubes with bad ballast, and now with LEDs seeing the cheaper controllers with slow blink rates. Once you know how, the brain is a dumb rube waiting to be tricked. Only believe half of what you hear and none of what you see.
Oh, I just hooked it up to a square wave generator and an oscilloscope. I just played with the square wave frequency. It was 50 years ago, I don't recall values and such.
I worked at a television station years back that was designed in such a way that the lights going up the tower were powered by the separate phases of three phase AC with the one at the top powered from all three combined. This was pretty normal but what the engineer had done was rotate them at every level so that if a phase was dropped you could count the lights and quickly see from a distance that the power wasn't right. 4 lights was good, 3 meant you dropped a phase, and so on. I thought it was a pretty clever way of keeping light on all sides of the tower while being able to tell from a distance that a phase was out.
This is best practice for anyone who uses three phase power.
A machine shop should connect 1/3 of their lights to each phase so it is immediately obvious if a phase gets dropped. Lots of equipment will suffer on two of three phases but with lower performance or even damage.
At work we run a lot of machinery with motors and its obvious when phase loss happens. From my office I can tell if the lights go out/dim and the usual shop "hum" becomes a buzzing grunt that is immediately identifiable. Older machines have to be manually powered down but the machines I rebuilt have phase loss protection in the PLC thanks to a power monitoring terminal in the IO (Beckhoff EL3453.) Since the PLC is on 24V DC I have a capacitor backup module fronted by a 24V PSU that takes the 480V three phase power which tolerates a phase loss. The machine safely stops the process and shuts down the pumps and any other AC loads, then waits to be manually powered off as the PSU and DC side doesn't care.
I was told that you want lights on all 3 phases so that you can see spinning things spin. If the lights are on single phase, they will dim 120 times a second, and the strobe effect can cause spinning things to appear stationary. With 3 phase, at least 1/3 of the lights are lit all the time.
That's a valid reason too. In an industrial environment full of rotating machines, thinking something is stationary because it's on the grid's natural frequency can be lethal.
It's way less of a problem with modern machinery, and leds will blink in uncorrelated phases in a frequency that is different from the grid's anyway.
For residential lighting running off a single-phase supply, there are some annoying LED bulbs with simple half-wave rectification that strobe at the grid frequency with less than a 50% duty cycle (often seen with bulbs emulating vintage exposed-filament bulbs with no frosted glass). It would be interesting to see how much less annoying that kind of flicker is when you have a three-phase supply to a light fixture, so that at least one set of LEDs was illuminated at all times.
There are no light fixtures that use three-phase power. At least that’s my belief, as I’ve never heard of one or seen one and I’ve been working in the electrical industry for almost a decade. You could theoretically arrange three lampholders like a delta or wye transformer [0] and connect a phase to each one and all three lamps will be lit, but the lampholders will be energized, so make sure to wear voltage-rated gloves when changing out the lamps ;) This is how three-phase resistive heaters are wired, the drop in ampacity and large resistive heating loads make it worth using three phase since ampacity is 1.73 times lower than it would be on a three-phase circuit than it would be at the same voltage as a single-phase circuit.
In the US, there are 208V single-phase and 480V single-phase lights that use two of the three phases. In practice, indoor lighting is either 277V (line to neutral on a 480V service) or 120V (line to neutral on a 208V service). Most commercial LED fixtures can use any voltage between 120V to 277V single-phase.
480V single phase is used for some pole lighting with long runs of conductors to handle voltage drop. Anything over 277V has to be elevated at least 22 feet off the ground per the NEC.
[0] https://en.wikipedia.org/wiki/Delta–wye_transformer
Back in the analog TV days, I could see the flicker on the 50hz PAL/SECAM signals whenever I visited Europe, especially when the screen was white and in my peripheral vision. I always wondered why it didn't drive everybody nuts, but then I got used to it. I did always wonder if there was a way they could have eliminated that (maybe they did in more expensive TVs that fired off at double the reference signal and not in cheap TVs in hotels/bars?).
simple answer is grid frequency in europe is 50hz, in the US and Canada it's 60hz.
Early TV's synchronised to the grid frequency (and drew the entire screen on each cycle) - also remember TV's where analogue to start with (and operated at large voltages/transformers) so if they didn't sync with the grid electrical noise becomes a big problem with the power supply.
In monitor terms it reduced jitter.
Yeah, I knew why. :-)
My brain immediately went into "solving" mode, though.
The 100 Hz TVs weren’t that common and had other issues. They weren’t strictly superior. TVs were supposed to use a different set of phosphors for 50 Hz that were less flickery at 60 Hz but in practice I don’t know if tube producers bothered to have different sets for the different markets.
How did that work, do you suppose?
How does one connect a lamp to 3-phase power?
Are/were there 3-phase fluorescent tubes available?
Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously? Without such malarcky as shadows or inverse-square to muddy our vision?
Or maybe a multiplicity of single fixtures with 3 tubes -- one tube per each phase?
And even then: Doesn't it still strobe somewhat at (50*3*2)=300 or (60*3*2)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
(LEDs are out-of-scope of this question, of course: Line-voltage LED lamps can have integrated electronics and can therefore have diode elements that are driven by things that approach [or even achieve] DC, which changes the rules.
And, of course: Incandescent lamps have enough persistence that stroboscopic effects are generally not an issue with a human eye.)
> How does one connect a lamp to 3-phase power?
You typically connect 1/3 of lamps on one phase, one third on another and so on.
In the UK we use a 230V single phase system for most things (industrial/commercial often use 400V) (if all three phases are in use it's 400V - you may see it as 415V but we harmonised with Europe to 400V) so lighting expects that 230V anyway, you still have a common ground, you just run the live for each phase to the lamp/light.
Power delivery to homes is in effect a single phase out of a three phase supply with each house (often but not always) wired in sequence, so house 1 is Phase 1, house 2 is Phase 2, house 3 is Phase 3, house 4 is phase 1 and repeat.
We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
> We have standard colors for this as well (as do most jurisdictions), neutral is always blue but the phases are Brown, Black and Grey
Never even thought about the fact that different regions may have different colour standards. This explains some of the power cables I've torn apart over the years and the strange colours I found inside!
> When I trained as an industrial electrician they where different colors, they changed in 2006 so that just makes me feel old (used to be Red, Yellow, Blue with Black for Neutral).
Making a mental note of that one... a black neutral would be a nasty surprise coming from North America.
Indeed, half my house is blue/brown, the other half is black/red since reg changes where grandfathered in and the wiring has been added to (some places clearly by a knowledgeable individual others..not so much).
I spent the first day after we bought it and moved in going around with a screw driver, side cutters a notepad and enough swearing to make a pirate with Tourette’s blush.
It’ll need a full rewire at some point, while I can do it myself to a commercial standard our regs require a currently qualified electrician sign off (mine expired many years ago) so I’ll just pay someone to do the lot.
It’s annoying but I’ve seen enough horror shows to see why it’s nescessary.
> Or are we relying on the spinny-thing that is to be observed to somehow be illuminated by all three phases, with three lamps or fixtures, simultaneously?
That's exactly what they mean, yes. Some lights on L1, some L2, some L3.
> And even then: Doesn't it still strobe somewhat at (5032)=300 or (6032)=360Hz, instead of the 100- or 120-Hz that a shop lit by a single phase might provide?
No, because the phases are overlapping, there is no point in time where they're all off. There'd be local dimming of course, depending on their position etc., but light for all of the second.
They're saying that you have 3 banks of lights, each connected to one phase of the 3 phase input. That way, when only 1 bank goes out, it's easy to see that one phase is out.
> This is best practice for anyone who uses three phase power.
No, it’s not. It’s a neat trick that visually reveals when the utility drops a phase, but there are better ways to handle avoiding equipment damage.
Best practice is to use phase monitoring relays that can de-energize a motor when a phase is dropped/reversed to prevent damage. The trip time is adjustable and it’s more reliable than manually hitting an e-stop. It also won’t let a motor with incorrect phasing start up either. You see phase loss relays on a lot of compressor motors and other large motors.
Here’s a flyer for an Eaton product: https://www.eaton.com/content/dam/eaton/products/industrialc...
Clever! I know I talked to the folks at Masterclock in St. Louis recently about one of their clock displays; they intentionally default the separators to flash if the clock is not synced to NTP, and then they go solid once the connection is established.
It's a quick way to know if something is down, using context clues that are already there to begin with!
Fascinating
Phascinating
I couldn't help myself, downvote at will.
> Joe: [...] So whenever there's a project on the tower, it's not unusual to see the guys in some kind of a, what do they call those?
> Jeff: A full ghillie suit? Or I don't know what they're called.
If you see someone up in a tall tower wearing a ghillie suit [0]... that sounds like time to call emergency services while avoiding their line-of-sight. :p
(Perhaps they meant "Hazmat" [1])
[0] https://en.wikipedia.org/wiki/Ghillie_suit
[1] https://en.wikipedia.org/wiki/Hazmat_suit
Haha, yes. For some reason, ghillie suit was the only thing I could think of at the time. I think they wear basic tyvek suits while doing paint work, not sure if they need full hazmat (maybe if the tower has lead paint?).
I can’t imagine why they’d need a hazmat suit either. It’s probably just protection from the cold.
Seems to be needed only for old towers:
> Tower painting has changed a lot over the years. The older towers have lead in them. So whenever there's a project on the tower, it's not unusual to see the guys in some kind of a, what do they call those?
> If you see someone up in a tall tower wearing a ghillie suit
My first thought would be “that might be the dumbest sniper I have ever seen”…while I was taking cover, because even if they are dumb, they might still be a capable marksman.
I imagine that a properly constructed ghillie suit covered with chain link fencing, barbed wire, no trespassing signs and a blinking red light might go undetected...
FAA details the marking and lighting requirements here: https://www.faa.gov/regulations_policies/advisory_circulars/...
One interesting fact I learned in a different discussion is that when LED lights are used for obstruction lighting, the FAA has standards that require infrared emitters to make them visible to night vision goggles, since unlike incandescent bulbs, some LED's can be invisible to NVG's.
https://www.faa.gov/sites/faa.gov/files/airports/engineering...
That is one of those wonderful facts that's both interesting and in hindsight completely obvious.
Speaking of, I was recently looking into what exactly makes lights NVG compatible, and found this informative PDF: https://www.consolite.co.uk/wp-content/uploads/2017/05/Basic...
tl;dr NVGs are sensitive to near IR so you want lights that are dim in those wavelengths (but not completely out since you still want to see them with NVGs) while still being bright in visible light. There's a neat picture of the flying controll tower on one of the UK's Queen Elizabeth-class aircraft carriers that shows two rooms with similar illumination levels in visible light, but under NVGs one room which isn't NVG compatible is massively brighter than the other. In the NVG-compatible room there were still a handful of panel indicator lights that were not compatible and lit up the whole space
I love the narrative storytelling here, but the takeaways seem somewhat obvious.
Lights on towers mean stuff, especially to airplanes.
Lights are required for tall towers, and get this, towers next to airports.
You can guess how tall a tower is by looking at the lights.
"My license to operate the tower is contingent upon my ability to appropriately light it."
These beacons are also great for navigation. Aeronautical charts usually show the color/pattern of the light. You can use those as points to triangulate your position.
You have brought back to me memories from 30+ years ago, playing Microsoft flight simulator, trying to triangulate my position using VOR beacons as quickly as possible before my aircraft had moved so far on that I was no longer anywhere near my triangulated position, hah!
I never appreciated how realistic FS was until I started studying for the navigation part of my PPL. I flew a 172 too so the instruments felt very similar.
IIRC, light houses are marked on charts similarly. The lights have different patterns, maybe color too?? Maybe not on aeronautical charts though.
Lighthouses are usually white. They used to rotate (sweeping the beam) but tend to flash now I think. Nautical charts show the elevation of the light, the visibility ranges and the pattern of on/off (eg Fl (2) 10s 41m 17NM). Some lights are sector lights, so red/white/green depending on your position, they indicate if you are in the correct approach channel.
It can be really confusing approaching a port at night. Never mind the city lights behind, and the cars driving about. 20+ lights flashing at different rates in the dark, some of them disappearing for seconds at a time. Oh, and if you turn your light on to refer to the chart, there goes your night vision!
Boat masts above 25m also have blinking red lights for the low flying aircraft (I guess its a bragging point)
Slightly off topic: typically, lights of neighboring towers blink asynchronously. But sometimes they are synchronized. Very satisfying. Anyone knows how this works? My best guess is e.g. DCF77. Thoughts?
I believe it's usually GPS/GNS (they all receive the time via GPS independently, and flash at predetermined times). The FAA requires synchronization for many classes of obstruction because it makes it clear that you're looking at obstruction lights rather than e.g. brake lights or traffic lights on the ground.
Could they also use power grid sync? Not sure as I haven't talked to anyone in wind power, but grid sync would be pretty close to 1 Hz at least in the US.
Building a product that would sync at 1 Hz via GPS that works in the US and other countries with 50 Hz power would be a little easier than syncing to grid phase though.
You can have each tower derive a perfectly stable 1Hz signal from the mains, but you have no way to synchronize those signals. Each tower's 'tick' starts at a random point in the 60Hz cycle.
You need an external, dedicated channel for this. You either synchronize with signals sent between towers or with a global signal from somewhere else (space). GPS broadcasts atomic time references for free, so everyone just uses that
Just like a freeway, public good and public benefit are things government should be doing well. (We the people, for us the people)
Definitely GPS. Other methods have been used in the past--I remember reading operating reports from a wind farm nearly 20 years ago that slowly brought all its lights in line with each other over several months--but these days you can buy mainstream lighting with the GNSS receiver built in from a number of suppliers. They make it easy.
For wind farm use most also have an external input for ADLS triggers, though that usually also requires a separate controller and communications connection to manage the ADLS signals.
The flashing red lights are L-864 type. The requirements are 20 to 40 flashes per minute (FPM), and typically 30 FPM is used.
Hmm... maybe I could build a 1pps GPSDO based on light flashes from nearby towers, then. No need for my own GPS antenna!
You'd probably have better timekeeping from a reasonably connected Pi with a common NTP daemon (take your pick, some are easier to configure / query), and a realtime-ish thread to emit your PPS signal on a GPIO or similar.
Probably more robust than line of sight, and able to pool with other NTP servers in your home-lab (and beyond).
True, but I'm not thinking of a practical method, just fun. I already have GPS derived time here, but that's been reliable and boring!
My observation is not that they are sometimes synchronised, but some subset of the towers are synchronised (this was my observation in Melbourne AU). Upon asking reddit, it appears that it is the FAA-preferred option that all lights are synchronised: https://www.faa.gov/documentLibrary/media/Advisory_Circular/...
I’ve driven through wind farms where the blinking tower lights are synchronized. Highly distracting.
If you look close - almost impossible in the dark - you will see that most wind turbines don't have any lights at all. Too many lights is a distracion but all the synchronized lights are an easy to understand 'stay away from this whole area'.
There are FAA rules on this.
Driving through a massive wind farm at night is a trip since they all blink in unison. Having them all independently would look interesting but could rapidly descend into madness:
https://archive.org/details/bigclive_20230516
When it's on purpose it's typically done through GPS driven clocks. This is how wind farms manage it, where all towers are required to blink together.
Yeah, I've seen it with windfarms. Always wondered why do they need to blink at the same time. The scale of the blink is pretty jarring at night (but also awe-some, in the same way any big enough infrastructure project inspires a kind of awe).
Wind farms have a certain amount of nimbyism because they "spoil the natural landscape." (So do regular farms -- nothing natural about grain silos or row crops, but that's a side topic...) Anyways, having that many towers blink in unison across that big a landscape is a weird effect when you first see it. I think there's an argument that if they blinked independently it would feel more natural in a way.
But since the blinking is all FAA requirements, I assume it's to help identify all the individual towers from the air. I suppose if they were all blinking independently, it would be a predator-trying-to-focus-on-a-single-zebra-in-the-herd problem, except in this case the predator is a pilot trying not to crash into a turbine.
Sure would emit more subtle 'part of the landscape' vibes though.
(Which I guess is exactly what you don't want when you're flying above them. Sigh.)
It's so pilots see the entire wind farm as a single entity and can interpret what they see and understand the extent of the wind farm easily. There is a pretty good study you can read on this:
https://www.airporttech.tc.faa.gov/DesktopModules/EasyDNNNew...
As to community impact, radar-activated lighting is an approach that is being used in places this is a concern. It allows the lights to remain off unless there is a plane within the envelope that requires the lights to activate. It's expensive though.
Does it have to be radar? Can it use ADS-B?
Little cropdusters and sport aircraft are who the anticollision lights are designed intended to protect, and many of them are not ADS-B equipped.
In the US, ADS-B is not required below 10,000 feet and when more than 30 miles away from the 30 largest commercial airports.
This is a safety measure. You can't rely on ALL aircraft having functional (or installed) transponders. You must actively sense incoming craft because they don't always politely announce themselves.
At small unattended airfields, you can sometimes turn on the field lights by transmitting on a particular frequency (as if you were calling the non-existent tower in quick succession).
https://www.aopa.org/news-and-media/all-news/2017/march/flig...
(Of course, in this case it works because the pilot already knows the airfield is there.)
The FAA document says "sensor-based" but every installation I have seen in the US uses radar.
> Always wondered why do they need to blink at the same time.
presumably this makes it more striking, and thus easier to notice and avoid
One option - Maybe the blinking time is set to a INDEPENDENT? accurate time piece - ie Blink on the change of a second
That's what DCF77 is. Or GPS.
It's probably just a side effect of them being powered on at the same time or not?
If they don't sync to a common clock source, they won't stay in sync for long. Probably not even for a few minutes or so.
You'd get the same phenomenon that you see when operating turn signals in traffic. They seem to weave "in and out" of sync. The frequency at which that happens is the beat frequency, i.e. the difference between the two blinking frequencies.
There's got to be some rubidium frequency standard that's a drop-in replacement for a 555 timer ;)
A chip scale atomic clock (with a handy 1Hz output) can be yours for barely over five thousand euros and half that if you buy 250 of them. https://www.microchip.com/en-us/product/csac-sa65
It's a bit larger than a 555, but it should keep you within a small handful of microseconds per day until the aging effects start to add up which make getting more than a millisecond a year dicey, even if the thing doesn't die on you: https://www.ipgp.fr/~crawford/2017_EuroOBS_workshop/Resource...
GNSS (GPS) is the typical standard used.
A cheapo 20ppm quartz watch crystal definitely doesn't drift by a second every few minutes, but it will over about about half a day at maximum error. A 5ppm one (still sub one Euro) will keep a second about every two days. A 0.5ppm TCXO can be had for about 15 Euros from Mouser and that gets you two weeks.
If you have shared line power you can just use that and everything will be locked in sync forever.
If you don't want to use that or radio, and you are outside, you could try to be really clever am sync your flash phases to a specific position of the sun. This is what the Long Now clock does. It'll be a different time each day, but it'll be the same for all units, within a small tolerance.
Well, yeah. I was sort of assuming that you won't use a TCXO or even just a cheapo quartz crystal, because it doesn't make a lot of sense: You've now thrown money at something that will relatively quickly desync anyway.
I mean, sure, the TCXO will mean that you only start seeing a phase difference between the two after weeks instead of minutes, but what's the point of that? I you want them to be at the same phase, you'll need to sync them at some point, and you do that by using a common clock source.
So either you shell out some effort for a real solution (power line is nice, and also qualifies as a common clock source as I've predicated), or you don't. And if you don't, there's no point in using a precise-ish clock at all, and you'll likely end up with very quick desyncing.
Well yes, obviously, but I'm just being a internet pedantic about "a few minutes".
And you are technically correct, which is the best kind of correct anyway.
Wouldn't the mains frequency be a common clock source, if nothing else?
But presumably these lights at least have battery backup, given the obvious risks in case all of them were to fail at the same time due to a grid issue.
Yeah, the mains frequency qualifies, if you explicitly use that.
(Doesn't solve the problem if you want them to be in sync phase-wise, i.e. blink at the same time or similar, but at least they won't drift apart, which was what this is about.)
You could still sync with that signal because it's not perfect.
For example, say you have a scheme where a period longer than the last one is symbol A, about the same period is B and shorter is C. You will get a random-ish sequence of symbols.
If you have an algorithm that, say, resets the timer to zero whenever a certain symbol sequence is detected, you can eventually get back in sync. With some care you can make sure you only sync when the sequence happens and the light has only been off for a short period to avoid excessively long off periods or truncated on periods.
Then you just need to have a local oscillator good enough to do that timing analysis and that can maintain sync between these symbol occurrences.
You could do it on the tiniest micro. Once you've counted the zero crossing detector, these days you might save 3 to 5 whole dollars over a GPS receiver on your very expensive ICAO compliant lamp and also ruled out using DC into the bargain! And theoretically it desyncs when the grid is too stable for days on end (and you just get BBBBB or ABABAB for millions of cycles)!
In terms of what is actually used, they do often use GPS and many of them have MODBUS or similar data connections which presumably wire into the wind turbine's telemetry somehow for fault detection.
Maybe you'll get a kick out of this, I did it in a bored afternoon a while back:
It is entirely self-contained (but needs zsh, not bash, for dumb reasons). Terminal at 90 columns works best.It is just a very simple integer LFSR as a random number source, followed by a hand-made integer IIR filter (manually placing poles on the z-plane). All of this entirely with trivial integer operations only (effectively using 32 bit fixed point arithmetic)
So without any external input or tools at all, and not even using zsh's $RANDOM, it makes an "analog" weavy pattern.
The LFSR is this part:
The hand-made filter is this part: I specifically tuned the filter peak just slightly away from being an integer divisor of 90 columns, to give the pattern a slight "rolling" effect.*What... the... fuck. Mind blown.
The zsh dependency is super unfortunate, though :(
It is amazing! With some brutal hacks to some array indices, and probably some excessive quoting changes it can work in Bash too:
This could probably be submitted to https://github.com/attogram/bash-screensavers/blob/main/gall...that article is incredibly hard to read. Luckily, an AI can summarise it in seconds.
This blog post has a really verbose format.
TLDR; White lights are used during the daytime, red lights at night (less annoying), towers under 200 feet don't need blinking lights.
It's a transcript of the video at the top.
> It's a transcript of the video at the top.
Which is not obvious at all if you have JavaScript disabled by default, since it only shows up as a blank space, which could also be a blocked ad or an image which failed to load correctly.
The first few times I saw one of these transcripts with video at the top (IIRC, it was on Practical Engineering, not this site), I thought it sounded odd but didn't get that it was a transcript. Only later did I find out that there were videos (and they're great).
Wow that wasn't clear to me either, thanks for pointing it out
Yes, reading transcripts is a terrible way of ingesting information in my opinion.
But at least you can scan and read through it instead of having to sit through an entire video :)
and thank you for doing it, at least!
next, you'll be expected to turn that into an outline, index cards, and then a full term paper lest you be ridiculed for your work on the internet!
Then go watch the video? What are you asking for here?
I'm not asking for anything. Just commenting that transcripts of videos make for bad blog posts. I'm not interested in watching the video.
Ah, not interested in the video, that clarifies it, thanks.
In the past year or two they have also added a quick periodic flash of white light for when visibility is low; like a camera flash that happens every few seconds. I think it was added this spring but don't quite remember.
It's not just radio towers. I've seen aircraft warning lights on tall buildings, particularly those near airports.
see https://www.ecfr.gov/current/title-14/chapter-I/subchapter-E...
mentioned in the article
Changing a radio tower light bulb is not for the weak of heart: https://www.youtube.com/watch?v=9b9LahaBJIk
Related: Some wind turbines apparently only turn on their position lights when there's any aviation traffic nearby (as detected by either local transponder interrogators (possibly ADS-B receivers?) or radar)!
Radar, called Aircraft Detection Lighting Systems (ADLS). The requirements are summarized in the FAA Advisory Circular covering aviation marking and lighting.
As far as I understand, non-US systems don’t always use (primary) radar.
Figured it was something to do with aircraft communications.
I live near an airfield and the runway has flashing white lights at night to help guide the aircraft's.
Blinking the lights also helps prevent bird deaths - https://en.wikipedia.org/wiki/Towerkill
At my work we are working on automating NOTAMs when our tower lights go out.
Never seen a blinking light on a tower in Norway. Why the difference between countries, can’t be that huge difference risk if some don’t have them?
In Norway this is regulated by Luftfartstilsynets BSL E 2-1, and the blinking white lights on our towers are called "hinderlys", for example category "Høyintensitet, type B".
They are not uncommon in Norway.
If you go to one of our major airports you will see one on the tower. The blinking lights also sit on wind turbines and TV masts, and anything taller than 15 meters in rural areas or 30 meters in populated areas will have some kind of light on it, sometimes blinking, either red or white.
Strictly speaking they should be unnecessary because there are published minimum safe altitudes for every air space over land. But some aircraft must be able to “See and avoid”
the towers in my area all switched to LED recently. the slow, glowing blink of the incandescent ones probably isn't as visible as the modern ones, but I do dearly miss seeing it out my window.
Why do some radio towers NOT blink? Is the better question.
Their height. Below a certain height, lights are not required
Blinking uses less power.
Blinking attracts attention which is the real purpose. I'd assume based on how we detect motion more easily, these add a bit of "motion" to attract our attention
I know. But when I was programming LEDs for my single board computer, I found that blinking the LEDs used a lot less power. If the blink rate was fast enough, your eye did not distinguish that from the LED being on 100% of the time.
I don't know if battery powered devices generally use that trick or not.
all dimmable LEDs use blinking, but interesting case for your suggestion for an even more efficient use of a "steady" LED. what blink frequency did you use to keep it from being visible to the eye? did it not dim the overall brightness to a meter? early LEDs were atrocious with their slow blink rates that quickly scanning across them could see it, but even more noticeable if you pointed your camera at them. now, they blink incredibly fast, fast enough even for some slo-mo to not strobe.
You only need about 40hz to make it seem on all the time, TVs (before 2020, maybe earlier) only did 25hz-ish. You can actually play pretty ridiculous tricks on the brain if you know this. For example, in VR, in a large enough room, you can slightly alter the angle the player sees inbetween frames. This alteration makes the brain think youre slightly offset from where it thinks you should actually be. This allows you to cause a person to walk in a circle irl, while they think they are walking in a straight line. Unfortunately only works up to a threshold of change, before the brain starts getting confused and causss the user motion sickness.
Fwiw, these "tricks" are nice for some, but cause headaches for those who're PWM sensitive (like me). I can easily see the flicker of eg my Pixel 5 screen (which iirc is around 300ish hz?), and it hurts my eyes.
Fortunately, some folks like Philips make bulbs that are very low or zero flicker.
>TVs (before 2020, maybe earlier) only did 25hz-ish
tell me your European without telling me.
> You can actually play pretty ridiculous tricks on the brain if you know this.
I do random persistence of vision tricks all the time. I can see flickering in cheap CFLs or old tubes with bad ballast, and now with LEDs seeing the cheaper controllers with slow blink rates. Once you know how, the brain is a dumb rube waiting to be tricked. Only believe half of what you hear and none of what you see.
Oh, I just hooked it up to a square wave generator and an oscilloscope. I just played with the square wave frequency. It was 50 years ago, I don't recall values and such.
I mean, that's just PWM dimming, right? AIUI, pretty well ubiquitous for all LED dimming, including battery-powered.
muuuuch better article, lol
https://www.jeffgeerling.com/blog/2024/what-happens-when-you...
To clean their eyes?
Flugwarnbefeuerung