davmax wrote:Blakey. Your defintion of the Candela measure is correct. However focusing determines how much light is crammed into the cone ie the flux density (candela) level.
The purpose of a reflector is to gather up the light emitted in all directions and concentrate the flux.
Please check out light intensity curves of LEDs in candela or millicandela, most commonly found in focsed LEDs data sheets. By measuring candela at different viewing angles a graph in candela intensity can be plotted over an arc of angles.
Candela is a candle power measure. A Lux mter can measure Candela at 1 metre 1 Lux = 1 Candela
Why indeed are focused lights specified in Candela such as in the standards?
that bit you noted on intencity of light into that small cone, that i was unaware of, but your thing there is actually incorrect, its
1m^2 x 1 Lux = 1 Candela
but in the same sense
1M^2 x 1 Lux = 1 Lumen
only different is 1 uses distance^2 other uses area of portrayed light determined by the distance.
In that sense 1Candela = 1 Lumen, But it does not = that, as you have stated,
and if you know the angle of the light you can work out the candelas
candela is only how bright it looks in a small angle, not how bright it actually is, you can have next to no brightness, but highly focused, it will look bright, but its not actually bright.
Here is a table that gives angles, and cd/lm
just get your Lumens then times the cd/lm number to get a estimate of candela
beam angle........cd/lm
5.....................167.22
10...................41.82
15...................18.60
20...................10.48
25...................6.71
30...................4.67
35...................3.44
40...................2.64
45...................2.09
so if you have 200lm at 15 degrees, you go 200x18.60 and you get 3720Cd
Most LED lighting that has greater then mcd milicandela are expressed in Lumens. as with most thing that have a large viewing angle.
you can also get Lumens from candela, by dividing the cd/lm number, the same way.
also unless they are all focued there cd will be one for each not a total of all of them, so if there is 5 led's in the unit, each have there own lense, then they will have 5 cd numbers, unless they are all focused in the same lense
hope that helps