[PSUBS-MAILIST] Light Experiments

[Alan via Personal_Submersibles]

I put a temperature probe inside the housing of my 80W LED light.
The probe was up against the acrylic lens, as I was concerned about
what temperature the lens was seeing on the inside. The lens is 10mm 
away from the LED.
The LED manufacturer told me that on normal LEDs the temperature
out the front of the LED can be 338F (170C) but my flip chips should 
run cooler.
Briefly; when run at 30W in water they stabilised at 257F after 5 minutes.
At 45W they stabilised at 280F after 5 minutes. I stopped upping the amps
at this stage.
Next experiment, I filled the housing with silicone oil.
At 45W it hit 116F in 4 minutes & temperature stabilised.
At 76W it hit 139F in 6 minutes & stabilised.
So oil has massive advantages in lessening temperature on the lens,
maybe because it is a buffer from the radiant heat & also transfers the heat
out through the housing quicker.
Greg your thoughts would be appreciated on this; I am thinking that without the
oil the acrylic lens would see temperatures at which it is formed especially
if I went up to 80W. Although the outside of the lens was cold there would be a 
temperature transition across the thickness of the lens & it would be considerably
weakened. I am building to 500ft, so it would potentially see 250 psi in operation.
   At this stage I haven't made up my mind whether to go with a borosilicate lens
or oil fill with an acrylic lens. I had a large bubble & it would be hard to eliminate
all bubbles in the oil filling process.
Will try & attach photos.
Alan
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