DIYbanter - View Single Post

On 3 Mar 2005 14:10:19 -0800, wrote:

Perhaps I'm missing something, but aren't you going to lose a lot of
optical efficiency with an offset feed unless you perform a somewhat
difficult change in the shape of the reflector to compensate for
off-axis illumination?

No. Perhaps "offset feed" was misleading. "Assymetrical feed"
might have been better terminology. The light source is still at the
focal point of a paraboloid. Since the Luxeon is not
omnidirectional (as a lightbulb is), I'm simply orienting it to
maximize the amount of its light that hits the reflector rather than
going forward without hitting the reflector, and eliminating unused
portions of what would otherwise be a full paraboloid to get a low
profile.

Satellite TV antennae work the same way; the dishes are sections of a
paraboloid with the pickup head positioned so it doesn't obscure the
dish's "view".

Since you have a computer, run a simple ray-tracing program and see
what the results are.

Did that with MathCAD, got an intensity plot. The real-life spot on
the wall looks very similar to the simulation results.