BRIGHT Lights

[zdas04]

I was driving this evening in Texas south of Lubbock (north of Snyder) and I saw a very large number of very bright red lights about 10-15 miles in the distance. These lights were about 40 ft above the ground and flashing on for about 10 seconds then off for about 5 seconds. All of them were flashing together and there were a bunch of them. As I got close to them, I saw that they were all on wind turbines. I figured they were navigational aids, but when we got behind them the lights weren't visible anymore.

I figure for them to be that bright that far off they had to be at least 1,000 watts. Does it seem to anyone else that a 270[°] visible very bright light would use more of the total output of a wind turbine than could possibly make economic sense?

David

 

[VEBill]

Driving at night in Texas with strange lights in the sky. I thought that this was going to be a UFO story... ;-)

 

[MikeHalloran]

I'd guess the lamps had Fresnel lenses and incandescent bulbs no larger than 150W, run at reduced voltage (or rated higher than normal) for extended life, or arrays of LEDs run on pulse power.

This document is almost on point:

http://www.airporttech.tc.faa.gov/safety/downloads/TN05-50.pdf

The specification of 3 degrees of vertical beam spread strongly suggests that the devices referenced within the document are equipped with Fresnel lenses.

Also, the intentionally narrow vertical beam spread suggests that the lamps may not be visible from the ground at all on the 'low' side of a gently sloping plain.



Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

A similar reflexion.

Those new LED traffic lights are many times very bright. So bright that it is difficult to see any person or animal or obstacle close to them on a dark winter night.

Are there any studies on this? Light levels were a lot lower when incandescent was used.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[MikeHalloran]

I think the standard USA traffic light's incandescent lamp is either 60W or 75W, derated to a lower than usual color temp and reinforced for impact resistance, and specially labeled as a traffic light bulb. Great for droplights if you can find them.

The first 'screw-in' replacements were apparently 'designed' by persons who didn't appreciate the sort of transients you can generate by interrupting a transformer, and failed early. Recent units are clearly more reliable, and thanks to progress in LED construction, much brighter.

I found a paper:
cogprints.org/2486/1/led.pdf
It appears to be based on human response experiments with simulated light sources. When it was written, green and amber LEDs were not superbright, and some concern was expressed about matching their apparent brightness to red LEDs. That issue later became moot.

This article:

http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/question178.htm

... cites efficiency, long life, and increased brightness as primary reasons for adoption. I found no papers or discussions about 'too bright' in the context of traffic lights.

I'd have to say that adoption of LED lighting has been somewhat rushed since greenazis invented efficiency, long life implies lower lifecycle costs, and increased brightness Sounds Like A Good Thing.

I personally find late model Cadillac brake lights, obviously pulsed LEDs, extremely distracting and blinding, but IMHO it will take measurable blood on the streets before anyone will question The Guvvamint about maybe having overdone their enthusiasm a little bit.




Mike Halloran
Pembroke Pines, FL, USA

 

[TheBlacksmith]

I don't have the article handy, but I read that in the snowbelt, the new LED traffic signals can get obliverated by blowing snow; the LEDs don't generate enough heat to melt the snow. They added heaters to the sheilds to melt the snow, somewhat negating the energy savings, although I suspect the heaters are thermostatically controlled and don't run all the time.

 

[waross]

In the 60's the standard incandescent traffic lamp was 69 Watts, clear.
A trucker friend tried LED clearance lamps on his tanker. After a winter of problems with early failures and not enough heat to melt the snow and ice, he changed back to incandescent lamps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[TheTick]

Atmospheric refraction.

 

[MikeHalloran]

Oooh, that's going to be another unintended consequence of government meddling. When incandescents become unobtainable, we'll need to tool up deicing heaters for the LED lamps.

Mike Halloran
Pembroke Pines, FL, USA

 

[zdas04]

The LED traffic light thing is real. Where I live (Northern New Mexico, at 5,300 ft elevation) they changed about half the bulbs from incandescent to LED during the summer about 5 years ago. First snow storm of the season hit on Halloween like it always does and all the south-facing and west-facing lights filled up with snow (strong winds from the SW). You couldn't even see color through the snow. Crews were out all night scooping it out. Next storm hit in early December and it happened again. Apparently back then it wasn't a simple screw-in screw-out change and we dealt with traffic lights not working very well until March. I never did hear if they went back to incandescent or installed heaters, but the number of fender benders was WAY up.

David

 

[BigInch]

Might try burning the swamp coal seam gas to heat those lights. Seems to be pleanty of it around there, or is it the mushrooms again.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[TheBlacksmith]

I did some research after I posted, apparently one of the better tricks some DOTs learned is to drive around with "super soaker" squirt guns full of polypropylene anti-freeze and spray the lenses. How come I never see these cool jobs advertised?

 

[zdas04]

There is a touch of CBM around here, but the lights are not Class 1 Div 2 rated so the nanny society would reject your gas heater idea out of hand.

Our municipal guys apparently never came across the super soaker idea, they are more towards gloves and trowels.

David

 

[JStephen]

The original post reminds me of an experience I had many years ago. I was driving out west of Wichita Falls, in the middle of nowwhere. Ahead and off to the left, I could see what appeared to be an illuminated road going up a mountain. And there are zero mountains in that area. So I drove and drove and finally got up closer where I could see what it was. It was a plume of steam from a generator plant, drifting back at an angle, and illuminated by the plant lights.

 

[BigInch]

Similar experience. I was driving from St.Paul to Duluth one cold winter night and there was what looked to be a very powerful floodlight pointed up into the sky. It was a bit strange out in the middle of nowhere and I wondered what was going on as I anxiously waited getting closer to see what I thought would be an immense circus tent or similar center of attraction under those lights. Problem is that I never seemed to get any closer. I started checking the milage. 2 miles, 5 miles, 10 miles, 15 miles, 30 miles ... and then it occured to me that for the first time ... I was seeing the northern lights.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[cswilson]

Skogs,

In the 1980s, I worked in a division that made LEDs as they were just getting bright enough to be what the marketing people were calling "sunlight viewable". As we looked for markets for these, one of the key starting points was always how many lumens were required in any application, and usually matching what the incandescents already supplied. We worked backwards from there. I would think that is by far the design approach used worldwide.

In coastal California, traffic lights are now overwhelmingly LEDs (we don't have the snow and ice problem here), and they have never seemed to me to be brighter than the incandescents they replaced.

 

[KENAT]

I don't know cswilson, except for the ones where 1/3 of the LED's have failed, I'm tempted to say they're brighter. However, it may be because the older ones I'm comparing them to are typically a bit crazed etc. on the window so look dull.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[patprimmer]

I think most traffic light lenses are polycarbonate these days. It certainly goes hazy and dull with age. It also solvent stress cracks so chemical de ice might need careful choice of chemicals used.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules