luxeons are full of goo

rox · Oct 14, 2002

so tonight i was trying to cut down my red lambertian luxeon star to get a wider beam pattern and i discovered something very interesting. its not a normal solid epoxy lens, its actually hollow and the inside is filled with something very like silicone. so dont try what i did or youll end up with something fairly useless. thoughts on this? i think it must be something related to heat issues.

Joshua · Oct 14, 2002

Craig once wrote on this subject:
"The silicone formula is there to reduce thermal expansion stesses on the bonding wires." The dice inside an LS does become quite hot.

hotfoot · Oct 14, 2002

According to Lumileds literature, the Luxeon uses no epoxy. Epoxy, as that used in most non-Luxeon LEDs, are prone to optical decay, thus resulting in decreased brightness over time. So, in addition to thermal cushioning, this goo seems to have the double effect of functioning as a non-yellowing encapsulant. This is good news since the epoxy in regular LEDs have been shown to yellow in as little as a few hours, the degree of which varies with the operating conditions of the LEDs themselves.

rox · Oct 14, 2002

thats pretty interesting hotfoot. i thought i had read most of the literature. now im curious what the outer hard casing is made of? the optical properties are closely matched to the goo.

hotfoot · Oct 14, 2002

I wouldn't put money on it, but I'm guessing polycarbonate or some sort of acrylic - maybe PMMA, the same stuff as the nx05s?

MicroE · Oct 14, 2002

Wow.
Goo.
Thermally conductie goo.
Thermally conductive optically clear goo.
I'm sure that the goo is also index (of refraction) matched to focus the light onto the lens.
BTW, high-power biological microscopes use "immersion oil". The oil is placed on the specimen and contacts the objective lens. The oil thus forms a direct path (no air contact) for light between the specimen and the objective lens. The oil allows the uscope to use less light and prevents the specimen from being fried.
These guys at Lumileds are bright, indeed.---Marc

Wim Hertog · Oct 14, 2002

Actually, the immersion oil helps to focus the light into the objective lens. No oil= fuzzy image...

luxeons are full of goo

rox

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Joshua

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hotfoot

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rox

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hotfoot

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MicroE

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Wim Hertog

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