On Wed, 16 Jul 2008 21:03:31 +0100, "ian field"
wrote:


"legg" wrote in message
.. .
On Wed, 16 Jul 2008 17:56:02 +0100, "ian field"
wrote:

Anyone know why some IRLEDs have a blue tinted encapsulation instead of
water clear?


1) It's benign?

2) It's cheaper?

3) For ident/differentiation?

4) Mechanical filtering?

I've seen infra-red leds with almost-black encapsulation.

RL

The almost black types are ubiquitous in consumer electronics as the
integrated IR receiver modules, I was wondering why sometimes blue when blue
is at the other end of the spectrum from IR?

Apparently the visible coloration doesn't always relate to
near-visible or IR transmission. Googling.... a Peacock Blue filter is
a black absorber under IR light, while the Congo Blue is transparent,
though one looks a 'lighter' blue than the other.

It turns out that the 'water clear' and darker tinted polycarbonates,
are grades that tend to be more stable with temperature - it's a
reliability issue, if not actually one of flammability.
(polyetherimides and polyethersulphones are probably too pricey here)

RL