Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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



Might this 'Heating the Phosphors' also explain why most CFL's need a while to 'catch hold'?
Certainly sounds like a valid hypothesis.
.
At 8:59 AM -0400 6/24/11, Spinozalens@aol.com wrote:

I am in the process of replacing most of my incandescent lights with LED
lighting. An interesting effect with these LED lights is that when they
first turn on they emit a somewhat purple colored light and are not very
bright. However , after a short time the light shifts to what the eye sees as
pure white light and they become as bright as the incandescent light they
replaced. I am pretty sure I know what is going on here , but if someone
knows better please make a comment. Here's what I think.

LEDs of course don't emit light over such a wide spectrum so as to
directly produce white light. You could combine blue, green and red LEDs to create
white light but this is very expensive as the efficiencies of the different color LEDs vary over a wide range and special circuits would be needed to
adjust for this. A more cost effective method is to use UV or blue LEDs and
broaden the light spectrum using phosphors.

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
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l