Why do some radio towers blink?

[skinwill]

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.

[xenadu02]

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.

[geerlingguy]

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!

[butlike]

Fascinating

[Terr_]

> 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

[geerlingguy]

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?).

[kcplate]

> 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.

[mr_toad]

I can’t imagine why they’d need a hazmat suit either. It’s probably just protection from the cold.

[scblock]

FAA details the marking and lighting requirements here: https://www.faa.gov/regulations_policies/advisory_circulars/...

[Johnny555]

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...

[alex_young]

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.

[themafia]

"My license to operate the tower is contingent upon my ability to appropriately light it."

[barbazoo]

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.

[gorgoiler]

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!

[dylan604]

IIRC, light houses are marked on charts similarly. The lights have different patterns, maybe color too?? Maybe not on aeronautical charts though.

[rollulus]

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?

[daemonologist]

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.

[askvictor]

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/...

[SoftTalker]

I’ve driven through wind farms where the blinking tower lights are synchronized. Highly distracting.

[rts_cts]

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

[scblock]

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.

[asdefghyk]

One option - Maybe the blinking time is set to a INDEPENDENT? accurate time piece - ie Blink on the change of a second

[winrid]

It's probably just a side effect of them being powered on at the same time or not?

[pizzalife]

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.

[jamesbelchamber]

It's a transcript of the video at the top.

[gchokov]

that article is incredibly hard to read. Luckily, an AI can summarise it in seconds.

[ofalkaed]

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.

[lxgr]

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)!

[scblock]

Radar, called Aircraft Detection Lighting Systems (ADLS). The requirements are summarized in the FAA Advisory Circular covering aviation marking and lighting.

[loph]

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...

[emmelaich]

mentioned in the article

[spc476]

Changing a radio tower light bulb is not for the weak of heart: https://www.youtube.com/watch?v=9b9LahaBJIk

[ortusdux]

Blinking the lights also helps prevent bird deaths - https://en.wikipedia.org/wiki/Towerkill

[not4uffin]

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.

[punnerud]

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?

[teslatree]

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.

[SoftTalker]

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”

[ck2]

muuuuch better article, lol

https://www.jeffgeerling.com/blog/2024/what-happens-when-you...

[wil421]

At my work we are working on automating NOTAMs when our tower lights go out.

[ikkun]

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.

[hinkley]

Why do some radio towers NOT blink? Is the better question.

[dylan604]

Their height. Below a certain height, lights are not required

[WalterBright]

Blinking uses less power.

[dylan604]

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

[Razengan]

To clean their eyes?

[LargoLasskhyfv]

Flugwarnbefeuerung

[satisfice]

Here is one nursing its young.

https://www.howitworksdaily.com/wp-content/uploads/2016/09/M...

[andrewflnr]

That's some crazy sexual dimorphism.