Light source at liquid nitrogen temps

[232Thorium]

Can anyone recommend a white light source to be used in a cryostat down to 77 K? We are using it in temperature-dependent studies of PV devices. Currently we have an incandescent bulb which has shifted its spectrum towards red over time and we're looking for a replacement. It would be nice to have a solid-state source since the incandescent bulb obviously heats up quite a bit, but I don't know of any that work at such low temps.

It should be a small bulb, about the size of the middle segment of a finger. (Weird comparison, I know, but I was looking around my desk for something that people on the forum could relate to for size and this does the trick .)

We'd eventually like to run a solar simulator hooked up to fiber optics to get the light down the cryostat, but for now we're looking for a new bulb as a temporary fix. Thanks!

 

[Andy Resnick]

Can you use an LED? Luxeon makes 5W white ones that are incredibly bright.

 

[232Thorium]

I would love to, but as I understand it, LEDs either suffer significant red shifting upon cooling or else stop working completely. A Youtube search gave some interesting demos of this. I will check it out and report back.

Also, I looked up Luxeon LEDs and they are all rated with an operating temperature of -40°C to +135°C, which isn't good enough for our experiments. I may buy one and see what happens outside of their listed range. Thanks for the tip.