On Mar 28, 4:24*pm, Mike Rocket J Squirrel
wrote:
On 3/28/2009 8:38 AM Frank Krygowski wrote:
On Mar 27, 11:11 pm, Nick L Plate wrote:
On 28 Mar, 02:08, Frank Krygowski wrote:
On Mar 27, 8:37 pm, Nick L Plate wrote:
Yes. I believe the lumen figure to be taken as the light falling
on a point away from the lamp whilst a candela figure is that
which is emitted by the lamp emmiter(bulb or LEDs). This would
make any candela figure innapropriate. The lumen figure would
also require a standard test (set distace, within a set
horizontal and vertical deviation, stadard colour, within a lumen
range).
No, lumens measure the total light output for a light source.
http://www.ledtronics.com/TechNotes/...d=13hasapretty
*good explanation for these confusing units of
measurement.http://www.westsidesystems.com/rays.htmlhasanotherone.
Dictionary check
lumen n a unit of luminuous flux - the light emitted in one second
in a solid angle of one steradian from a point that is a radiation
source of uniform intensity of one candela.
Again, the units are confusing.
Perhaps the simplest way to understand what lumens measure is to
examine a light bulb package. *The package of household bulbs I just
grabbed said "Total light output: *1600 lumens." *That explains it
adequately.
Reflectors and lenses concentrate those lumens, affecting the number of
lumens per steradian. *Projecting them onto surfaces affects the number
of lumens per square foot or per square meter. *But the fundamental
amount of light is measured in lumens.
Thanks, Frank, most helpful.
So, what units are the most useful to use to compare apparent brightness
of something like a tail light? And what units, if any, are the most
likely to be used by the manufacturer in their advertising? One hopes
there will be some overlap between the two.
--
Mike "Rocket J Squirrel"
Bend, Oregon
Frank has been trying manfully but light measurements are such a
minefield, you need to keep your wits about you even after you think
you mastered it, and then manufacturers of bike lights still play fast
and loose with the numbers in the hope of scoring an undeserved
advantage. At least Cateye measures all their lights the same way, so
you can compare between Cateye lights. -- Andre Jute