Why do some radio towers blink?

Posted by warrenm 10/28/2025

Why do some radio towers blink?(www.jeffgeerling.com)

179 points | 120 commentspage 2

loph 10/28/2025|

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 10/29/2025|

mentioned in the article

spc476 10/29/2025||

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

ortusdux 10/28/2025||

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

not4uffin 10/29/2025||

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 10/28/2025||

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 10/29/2025||

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 10/28/2025|||

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 10/28/2025||

muuuuch better article, lol

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

wil421 10/29/2025||

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

ikkun 10/28/2025||

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 10/28/2025||

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

dylan604 10/28/2025|

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

WalterBright 10/28/2025|

Blinking uses less power.

dylan604 10/28/2025|

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

WalterBright 10/28/2025||

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.

dylan604 10/28/2025|||

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.

CableNinja 10/29/2025|||

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.

user_7832 10/29/2025|||

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.

dylan604 10/29/2025|||

>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.

WalterBright 10/28/2025|||

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.

yjftsjthsd-h 10/29/2025|||

I mean, that's just PWM dimming, right? AIUI, pretty well ubiquitous for all LED dimming, including battery-powered.

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