On Sun, 14 Sep 2008 17:11:11 -0700, "Michael Koblic"
wrote:

This is interesting!
I am not familiar with their units of luminosity. What is it in Lumens?

Lumen is a unit of total light flux. Candela (cd) or millicandela
(mcd= 0.001 cd) is beam intensity in lumens per steradian, lux is
how brightly an object is illuminated in lux per square meter. The
most useful measure of brightness for photography is lux.

The width of the beam angle has as much to do with brightness as the
lumen output. In photography, the distance and extent of the subject
would determine the best beam angle, one which illuminates the entire
subject while not spilling much beyond it -- i.e., outside the field
of view.

Examples: 1000 lumens from a light bulb with no reflector produces
about 80 cd. At a distance of 1 meter the brightness would be about
80 lux.

With a reflector or lens forming a beam with 40 deg half angle (80 deg
included angle) those 100 lumens produce subject brightness of about
680 lx, beam intensity of 680 cd.

At 10 degree included angle (flashlight) it's about 40,000 lx on the
subject (at 1 meter) with beam intensity of 40,000 cd.

These are approximate because I've not figured in intensity
distribution within the beam. But they're indicative.

Some comparison points:

Bright sunlight about 110,000 lux
shade illuminated by entire blue sky, midday: 20,000 lux
Typical TV studio lighting 32,000 lux