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Re: [Phys-l] Interesting LED Light Effect- Reality Check Reques



In a message dated 6/24/2011 6:03:58 P.M. Eastern Daylight Time,
bill@ASTRO.AS.UTEXAS.EDU writes:

meekerdb wrote:
On 6/24/2011 1:28 PM, Bob Zannelli wrote:

> What I am pretty sure is happening is that the phosphor needs
time to
> heat up before it emits light over a broad spectrum, the purple
tinge
> reflects the fact that the LED's being used are emitting UV
light. I
> can't find anything in the literature on LED lighting that
talks about
> this, hence my post.
>
> Bob Zannelli


When in doubt, look at WikiPedia:

http://en.wikipedia.org/wiki/LED_lighting#Technology_overview

Bill



Bill , nothing I found in this article, talks about this. Did I miss
something?

Bob Zannelli

It does talk about using phosphors, but not about a time delay. I
don't think phosphors need to warm up, they're just providing energy
levels.

Brent


Yes, that's what's puzzling about Bob's report. A fluorescent takes a
second or two to come to full light, but that's just because it takes
that long for the emission from the mercury vapor to get to full
strength. I've never seen a change in color during this process, so I
don't understand why this should happen with a narrowband emitter like
an LED. So I hope Bob or someone does come up with something. It would
be interesting physics, at least.

Bill




)))))))))))))))))))))

It's definitely an effect that is heat related. After the light heats up
you get full light output instantly. The phosphors are going to heat up, in
the literature they are cited as a cause of lower efficiency. The photons
from the LEDs are depositing energy in the phosphor material . For LEDs
light is the output , heat is a byproduct, the exact opposite of incandescent
lights. What's surprising is that there is no information on this in wiki
or anywhere else. .

Bob Zannelli