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Posted by warrenm 1 day ago

Why do some radio towers blink?(www.jeffgeerling.com)
152 points | 99 commentspage 2
not4uffin 18 hours ago|
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.

spc476 22 hours ago||
Changing a radio tower light bulb is not for the weak of heart: https://www.youtube.com/watch?v=9b9LahaBJIk
lxgr 1 day ago||
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 23 hours ago|
Radar, called Aircraft Detection Lighting Systems (ADLS). The requirements are summarized in the FAA Advisory Circular covering aviation marking and lighting.
lxgr 23 hours ago||
As far as I understand, non-US systems don’t always use (primary) radar.
pizzalife 1 day ago||
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 1 day ago|
It's a transcript of the video at the top.
cesarb 10 hours ago|||
> 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).

skrebbel 1 day ago||||
Wow that wasn't clear to me either, thanks for pointing it out
pizzalife 1 day ago|||
Yes, reading transcripts is a terrible way of ingesting information in my opinion.
geerlingguy 1 day ago|||
But at least you can scan and read through it instead of having to sit through an entire video :)
dylan604 23 hours ago||
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!

mikestew 22 hours ago|||
Then go watch the video? What are you asking for here?
pizzalife 6 hours ago||
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.
mikestew 3 hours ago||
Ah, not interested in the video, that clarifies it, thanks.
ortusdux 1 day ago||
Blinking the lights also helps prevent bird deaths - https://en.wikipedia.org/wiki/Towerkill
punnerud 1 day ago||
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 14 hours ago||
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 23 hours ago|||
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”
ikkun 22 hours ago||
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 1 day ago||
Why do some radio towers NOT blink? Is the better question.
dylan604 23 hours ago|
Their height. Below a certain height, lights are not required
WalterBright 1 day ago||
Blinking uses less power.
dylan604 23 hours ago|
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 23 hours ago||
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 23 hours ago|||
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 18 hours ago|||
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 hours ago|||
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 17 hours ago|||
>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 22 hours ago|||
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 20 hours ago|||
I mean, that's just PWM dimming, right? AIUI, pretty well ubiquitous for all LED dimming, including battery-powered.
Razengan 1 day ago|
To clean their eyes?
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