I drive around the DE Valley all day, and I have noticed that there has been a definite change to the appearance of the traffic signal. It used to be just a plain white bulb behind a colored glass filter (lens?). Now, many traffic signals (esp. red or green - yellow is too short…didn’t notice) appears to be made up of several small dots. Even arrows have taken on this appearance! Overall, the color seems to transmit more clearly (many older green lights around here appear washed out) AND I believe they are more visible from a greater distance.
Is it still one bulb, or LEDs, perhaps? How does this work, esp if one bulb? Multiple bulbs (or LEDs) seem too high maintenance. Could the filter split one light source into parallel rays, and keep them parallel by using the properties of fiber optics, perhaps?
Also, as an alternate, if not dots, in DE esp., (where washed-out green lights were abundant), it seems they use a fine mesh in the colored filter which seems to yield the same enhancing benefits for clarity and visibility.
Oh, also…more and more tractor-trailers have this technology in their tail lights (both yellow and red tail lights).
Has anyone else noticed this change? How recent is this technology? When did they sneak around at night swapping out all the filters?
If you know about this trend and/or the technology itself,
please share…just curious!
Those are LEDs. They are supposed to last up to 100,000 hours. That’s 11 years - far longer than incandescent bulbs. And since the lights are made up of dozens of LEDs, it’s no big deal if a couple of them go out. I expect they just replace the whole array if too many LEDs go out.
LED has other advantages too. One is low power consumption. Incandescent bulbs produce white (or yellow) light so if you want a red light, the other colors are absorbed in the filter and lost as heat. LEDs produce monochromatic light so there is no need for a filter. LEDs also turn on and off much more quickly - tens of milliseconds as opposed to hundreds for incandescent bulbs, IIRC. This is a big advantage for brake lamps for cars and trucks. A car can move several few feet in the time it takes for a light bulb to turn on.
I don’t know when they became popular - they are far more popular in the US than in my country. On my recent trip to Houston I was impressed that all city buses had LED turn signals and tail/brake lights.
Funny you should say that: I noticed the opposite at some intersections. The signal actually goes blank when changing from red to green. It is long enough that I can notice it, and I never noticed the signal going TOTALLY blank, if only for a split second, with the conventional bulb.
Also, are these little LEDs more visible from a greater distance because there is no light-filtering material to pass through?
Thanks for the info, scr4…
Jinx
P.S. We’ve corresponded often on SD. You have the same initials as my roommate from college (and close friend). He’s now a Ph.D. in Astronomy, and I think you share similar interests…yet, you are in a different country (I believe you said). Still, you must be his twin… Wow - small world! Ironic, isn’t it?
I think the LEDs are more visible because they are monochromatic - i.e. the color is more “pure.” Though it’s also possible they are simply brighter. Since LEDs use less power and produce less heat, you can package a brighter light into the same housing.
p.s. How do you know my initials? My username isn’t it. (In fact my handle doesn’t really mean anything, I keep meaning to change it but I’ve been lazy.)
LEDs are wonderful. RElatively long-lasting, somewhat efficient, almost pretty, and can be arranged in arrays without fear of heat problems - much better than incandescent bubls.
The disadtvantage to LEDs (small viewing angle) doesn’t matter - many “old-fashioned” incandescent-powered traffic lights use Fresnel lenses to make sure that you can only tell what color the light is if you are almost in front of it. This is to make sure walkers and people on roads other than the watched light don’t go before their turn.
From what I’ve heard, this is independent of the use of LEDs (which can switch practically instananeously) - it’s a safety measure instituted to keep light-jumpers from pulling out too soon and hitting the guys still going the other way.
The narrow viewing angle is a common feature of commercial LEDs, but not an inherent property of LEDs. The light-emitting element is embedded in a transparent plastic, and the front surface of the plastic is convex. This acts as a lens and makes the narrow beam. If you want a wider beam you can just change the shape of the plastic. Or you can even grind off the tip of a normal LED.
Given the fact that traffic lights are often equipped with shields to prevent their being viewed at off-angles (at least, I assume that’s why they’re there), it would seem that narrow viewing angles is an advantage in this case.
I never thought much about it, but I assumed those shields were put there to cast a shadow on the lens and thereby prevent sunlight from washing out the traffic signal. I figured the reason they’re not everywhere has to do with the lay of the land, and the sun being prevented from washing out the signal light in many locations.
I think one reason they are being used more now is, in the past LED’s were only red. With the advent of LED’s in other colors (yellow, blue, and now white) they can be used in more applications.
And that’s excellent! Some jurisdictions are mandating their use. LED’s are cheaper as they last longer, and they use far, far less electricity, saving taxpayers money and even being good for the environment.
In my industry (broadcasting) high intensity LED arrays are beginning to find their way into obstruction lights for towers.
What’s fascinating (to me, at least) about this particular application is that the manufacturer of the fixtures has actually built a circuit into them to allow the LED’s to quickly “dim to off” instead of simply shutting off instantly. Apparently, people (pilots, presumably?) had a hard time with the instant-on / instant off character of the arrays. The “dim-to-off” circuit allows the LED array to more closely emulate an incandescent lamp when shutting off.
