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A wavelengh quiz!!

FireMyLaser

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Fffffffffffuuuuuuu-
 

aryntha

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It helps that I have a big giant box of organized "sample" LEDs... I had the Agilent 626/590/505 grouped together, and the Fairchild 625/590/505 grouped together though I thought to myself, "huh... that makes sense..."
 

FireMyLaser

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aryntha

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The green has always been blue-green; I'm not sure if this is a yield issue (505nm InGaN LEDs may have better yield and better lifetimes/POH) or if it's an issue of differentiation and visibility (getting the 'green' light to be 'far enough' from amber...)

I'm leaning towards the InGaN yield issue, but i've seen some "filtered" incandescent-sourced traffic light greens actually appear more blue-green.

Here's an interesting factoid though: Many languages and cultures do not distinguish between blue and green. (In many languages, the word for 'blue' and 'green' are the same.)
 
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Wow. This is cool. :D I've seen alot of different lights where I live, considering you can go from metropolis to farmville in a ten minute drive lol, the new LED lights in my area have a "greener" green than the old lights, and there's some red lights in collinsville that are so old thy're almost white... So ya, huge margin for me. :)
 

aryntha

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the new LED lights in my area have a "greener" green than the old lights
Hmm. This supports the "505nm due to InGaN wafer yield, not preferred color" idea even more... I know InGaN's "favorite" wavelength tends to be ~405-415nm. So the further away you get from that, probably the lower the yield.

Probably very VERY similar to the "it's hard to create a green diode" dilemma, since we're talking InGaN diodes, there, too.

So I'm guessing InGaN LED development is likely following and piggybacking off of InGaN laser diode development, and vice versa.

So that's probably why older LED traffic lights are blue-green and newer ones are "truer" green.. Just a guess though!
 

FireMyLaser

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In my town most of the green LED lights are just true green looking (~525nm). Just a few are in the 515nm area. But in this one intersection they are DAMN BRIGHT blue-green ~505nm. About 75% of the lights are LEDs now, the incandescent green ones look very pale. We also have white LED traffic lights for the buses and trams, and they too are very random in colour temperature (warm, cool, even purple looking). They all seem to be made by different companies and looks kinda stupid. :twak:
 

Pontiacg5

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Some of the traffic lights here have a blue bulb above the light that lights when the light is red. (too many lights? :D)

Others have a line through the middle of the red light that strobes white when the light is red, it really gets your attention.

Then we have the stoplights with 4 bulbs, one green, one yellow, one yellow arrow, and a red bulb. Sometimes the yellow arrow is steady, and other times it blinks and then other times you just get a yellow circle, then other times you get a yellow circle and a blinking or steady yellow arrow. To this day I still have no idea what the heck it means. I've come to the conclusion that it has something to do with KU students and testing peoples reactions to the whacked stoplights :p
 

aryntha

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The small blue -i believe- is to indicate to emergency systems that an override/sensor system is available at that light.
 
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well depends on the shade but my guess wpuld be its the same as a laser??
so green 352nm 624nm red, 585nm yellow and actually i dont think there is a correct answer becaus ei bet aussie traffic lights are different from USA ones.
cheers
 

aryntha

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As far as variance by country, LED suppliers are pretty much universal; and most of these traffic light manufacturers are outside of the US to begin with. The wavelengths available of InGaN and AlInGaP LEDs at given lifetimes, lumen maintenance, and brightnesses (at cost) are pretty much established. The LEDs come from Agilent (now Avago), Cree, Nichia, Fairchild, Uniroyal, Philips, and maybe a handful of others that I've forgotten. The market isn't that varied.

It'd make little sense for Australia to spend 4x as much on a given LED traffic light unit just because they prefer 532nm to 505nm, or 585nm to 590nm.
 




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