# Lens aligning various angle of incidence light striking it?

• I
Assume a flat one square foot vertical plate attached 6 feet up, outside on a wall.

Dozens of yards away are various solar reflectors angled to reflect sunlight onto that plate.

Problem is, the plate requires to be only struck straight on at a 0 degree angle of incidence.

And, all the reflected sources are striking it at some other angle up to 45 degrees off center.

Is there any lens or dome or reflective funnel arrangement, or something else altogether, that
could be put in front of the plate to take all those different angled incoming sunlight sources
and align them all, to next be exiting it to strike the plate behind it straight on at a 0 degree
angle of incidence?

Thank you for any thoughts or suggestions.

Drakkith
Staff Emeritus
Is there any lens or dome or reflective funnel arrangement, or something else altogether, that
could be put in front of the plate to take all those different angled incoming sunlight sources
and align them all, to next be exiting it to strike the plate behind it straight on at a 0 degree
angle of incidence?

There's no combination that could make all the light strike at exactly 0 degrees, but a simple negative lens placed near the plate might reduce the angle, making it closer to normal incidence (perpendicular to the plate's surface). I don't know what power or diameter the lens would need to be though.

There's no combination that could make all the light strike at exactly 0 degrees, but a simple negative lens placed near the plate might reduce the angle, making it closer to normal incidence (perpendicular to the plate's surface). I don't know what power or diameter the lens would need to be though.
Wonder if somebody has done a stacked arrangement of such lens, to progressively get average of off angles closer to zero?

Andy Resnick
Is there any lens or dome or reflective funnel arrangement, or something else altogether, that
could be put in front of the plate to take all those different angled incoming sunlight sources
and align them all, to next be exiting it to strike the plate behind it straight on at a 0 degree
angle of incidence?

Only if it is a lossy system, otherwise you violate the first law of thermodynamics (conservation of etendue).

Only if it is a lossy system, otherwise you violate the first law of thermodynamics (conservation of etendue).
Gotcha, thanks for your patience with me.

I was kinda imagining an optical cone or funnel of sorts, creating a more laminar flow of light as the angles reduced with every reflection, finally approaching 0 degrees. But, each reflection along the way loses a little power, yes?

I was kinda imagining an optical cone or funnel of sorts, creating a more laminar flow of light as the angles reduced with every reflection, finally approaching 0 degrees. But, each reflection along the way loses a little power, yes?

There are such things used by people doing non-imaging optics, e.g. a Winston cone is an example on a much smaller scale than what you need, but yes there is loss at each reflection. Do the rays need to have exactly 0 degree angle of incidence?

There are such things used by people doing non-imaging optics, e.g. a Winston cone is an example on a much smaller scale than what you need, but yes there is loss at each reflection. Do the rays need to have exactly 0 degree angle of incidence?
Pixel,
Thanks for Winston Cone tip, interesting.

I'm trying to get clarification from two hot mirror manufacturers, in regards to how transmission/reflectance degrades when AOI exceeds 0 or 45. They are optimized for either one or the other and earlier inquiry to Edmunds Optical regarding their UV/IR filters had them respond with; "...the angle of incidence is critical to the performance of the filter. If the angle is off, the efficiency will not be the same as the published specifications." Waiting to hear back now if that applies also to the hot/cold mirrors and exactly how much is too much AOI.

Drakkith
Staff Emeritus
Why does the light need to be at a near-zero angle of incidence?

Tom.G