I noticed some people working on a set of traffic lights near my home the other day and since then, I’ve noticed that when the lights change, the signals ‘flick’ on and off much more abruptly than they did before, I’ve also noticed that each coloured signal appears to be made up of a grid of small elements, i’d suspect that these were high intensity LEDs except that the green signal is not the conventional green LED colour; it’s much more of a blue-green (like ordinary traffic lights)
So, can anybody tell me what technology is being used here - is it LEDs or some sort of fluorescent display?
Those appear to be all the rage here in California suddenly. I’ve heard they’re made up of LED’s, and that the idea is 1) LED’s last much longer, and 2) they won’t fail all at once.
The ones around here seem to flash on in a way that makes it look like they’re actually brighter than normal right when they turn on, as if they’re trying to get your attention. I’m not sure if this is real or percieved.
Yep, you guys are right. The new signal faces are LED. Well, the ones they are installing in California and here in New Jersey are, anyway. I don’t know what they may have decided to use in the UK.
LED signals have several advantages over incandescent bulbs - Longer life (I have seen ads promising up to ten years of continuous use), up to 90% less energy consumption, quicker switching on/off, and better visibility at night and in poor conditions.
Oddly enough, I have occasionally seen plans that call for LED red and green lights, but not yellow. I am not the official traffic engineer around my office, so I don’t know the logic behind that.
Same deal here in Virginia. I spoke to someone in the transportation department and his logic was “The yellow lights take so much longer to burn out because they are only on for about 3 seconds, so it is not cost effective to replace them with the LED signals.”
Vex
maybe because you can’t make yellow leds. the yellow in scrollindg display boards ive seen are simply the red and green elements in a space on at the same time. hmm… why that would let you make traffic signals that are but a single panel! light the reds for stop, light the greens for go, light both for caution, and light in a pattern for “left turn only”! i bet there will be lights like that soon.
Red and green have longer on times than yellow, which makes them more likely to burn out. LED units cost more than normal bulbs. The whole thing is a lifetime operating cost question - the LED units (practically) never burn out, but they cost much more than the other bulbs. Say that an LED unit costs ten times what a normal bulb costs. This means that you have to replace a normal bulb ten times before you have paid out the same amount that you would pay for a normal bulb. If you don’t expect to replace the bulb often enough to reach the break even point (which actually would include the costs of sending a worker out to replace the bulb,) then you just go ahead and use the cheaper bulb.
You can get three-colour LEDs, which either have three pins (an anode each an a common cathode, or vice versa), or two pins, in which case they are red when the current flows in one direction, green in the other and yellow on alternating current (actually flashing very fast between green and red, but the eye sees yellow)
But there are such things as true yellow/amber LEDs
I don’t think my colorblind pals would appreciate lights like that. Many of them rely on red being on top and green being on the bottom. They wouldn’t be able to tell if the light was red or green if they were in the same panel.
i am sorry. i never thought of the colorblind when i said that. and thank you, i did not know that you could make amber LED’s (or white ones, for that matter).
but i do reiterate bathasar’s question. that makes me wonder too!