Re: Light gathering cone?



On Jan 25, 6:37 pm, nos...@xxxxxxxxxx (Paul Ciszek) wrote:
One way to concentrate light on a device without lenses (or the need to
aim precisely) is to build a narrow cone (frustrum, actually) with a
reflective interior surface. If the cone is made of solid glass and
silvered on the conical surface, then Snell's law works in your favor--
any light that makes it into the glass at all will be less than the
critical angle away from the axis, making it easier to reflect back
towards the center. I tried to work out how narrow the angle needed to
be to capture all the light, and saw there really was no such thing.
Eventually the light will start ricocheting its way back out of the
cone. So now I am wondering:

1) Does this device have a name?


What you want is either a compound parabolic concentrator or a compound
elliptical concentrator. Any ray tracing program would reveal that a
one is poor concentrator and that a lot of light does come back out the
large end of the cone.




anyone analyzed the problem? While there is no "magic angle",
it would seem that for a given ratio of exit size to entrance
size (i.e., gathering all of the light falling on a cirlce 2cm
across and concentrating it onto a detector 0.5cm across) there
is probably an "adequate angle". The optimal shape is probably
not a cone at all but a horn that flares out at the intake end and
has a progressively narrower angle and your progress toward the
outlet end.

--
Please reply to: | "Any sufficiently advanced incompetence is
pciszek at panix dot com | indistinguishable from malice."
Autoreply is disabled |

.