Andrea wrote...
>At 15.44 13/03/2004 +0000, you wrote:
>>Andrea wrote...
>>
>>>6) To increase further the range, I'm thinking about making a 2m long
>>>   tube, internally reflective (aluminium foil), diameter slightly more
>>>   than the IR LED. This should decrease the angle of emission, but also
>>>   make it more powerful and concentrated, right? (i.e. a bit like a
>>>   poors' wannabe laser).
>>
>>This doesn't work;  I've tried it.  Rather than narrow the angle
>>of emission it increases the angle.  You need a lens system of
>>some sort.
>
>Did you try with an internally opaque tube, or IR reflective?
>
It doesn't really matter; using a tube in that way, the only beam
"narrowing" you get comes from absorption by the tube walls; any
ray reflected by the walls comes out at the same, or greater,
angle as when it impinged on the tube wall.

Dave D.

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