Re: Lux with plain reflector?

On Oct 17, 2:02 pm, "I.N. Galidakis" <morph...@xxxxxxxxxxxx> wrote:
I suspect this is fairly basic question for lighting engineers, but in my mind
it has not been completely cleared.

Suppose that in a certain arrangement with a lamp under a dark opaque ceiling
the illuminance below (on say the reading surface [X]) is measured to be 100
lux.

--------- ceiling
[L]
\
\
\
\
\
\
--------[X] table

What would the reading be if the ceiling is replaced by a perfectly reflecting
mirror? Would it be roughly double (i.e. 200 lux at [X])?

Assuming an omnidirectional source of zero size, it would be just a
tiny fraction under 200 lux (for theoretical purposes, call it
exactly). Do this as a thought experiment. The mirror is doubling
the universe, effectively creating a second light source above the
first. The reason it would be a fraction down is that the source in
the second universe is a tiny bit further away - double the distance
between the light source and the mirror, so in a theoretical universe,
you could make that zero. The real light source would also create a
shadow from the virtual source, hence the need to consider it of zero
size. In the real world, mirrors also suck some small amount of
light.

Rick brought up the difference between radiosity calcs and raytrace
calcs. He's right, to the extent that radiosity software generally
models reflected light as being of lambertian distribution (jump in
guys if I'm wrong on this one!) but it is possible, if you're clever,
to model a mirror in a radiosity model by creating a second space,
mirroring the first, then directionality works.

Thought experiments are usually easier than calcs, and for extremely
simplified, unnatural circumstances, the assumptions made by
raytracers or radiosity software will cause inaccuracies, not improve
the accuracy in general.

Regards,

Thomas Paterson
http://www.luxpopuli.com


.

Relevant Pages

  • Re: Extremely Short Focal Length Parabolic Reflector
    ... > Edmund optics makes a parabolic reflector of the size and focal ... > I would like a parabolic reflector like this to increase the amount ... What kind of light source do you propose to ... not going to be matching the speed of the collimating mirror very well. ...
    (sci.optics)
  • Re: light source in 19th century experiments
    ... What the physicists used as light source in 19th century optics ... Without laser, how can they measure the speed of light by ... a mirror and a rapidly spinning toothed wheel, ...
    (sci.optics)
  • Re: How to measure form error on a huge concave mirror
    ... be brought to the mirror, ... Is there something like a Foucault knife-edge test or a Ronchi test ... If you place a light source (for either the Foucault or Ronchi ... tests) at the center of the radius of curvature for the center zone, ...
    (sci.optics)
  • Re: CRICKETS LOVE THE 40D!
    ... take a wild guess that the mirror, or some *other* light source has ... reflecting the omnidirectional light from the Gary Fong. ... take their picture in a mirror and post. ... Death of usenet: Film at eleven. ...
    (rec.photo.equipment.35mm)