Re: What is a \"deep\" reflector good for!?
Tom,
I am certainly no expert; merely an inqusitive student. I can answer to the best of my understanding.
If one had a perfect columating beam and it were in a vacuum where no light were lost to particles in the path, I believe your lux measurement would be the same at any distance. The quantum physics guys might pull out a photon or two (heisenburg uncertainty) or even add some (parallel universe /ubbthreads/images/graemlins/smile.gif ) but for our purposes, there would be no divergence in the beam. The inverse square relies on a lambertian distribution which you do not have if there is any columation or may I call it psuedo columation or bundling of the photon paths. /ubbthreads/images/graemlins/icon3.gif
I believe there is also a certain amont of convergence of light from our typical reflectors. If you take any of the turbo heads and bring the beam close enough to target, you will see a null that does not remain on distant targets. The more effective the columation, I believe the further you will need to go to have convergence of light cover this null that is the shadow if you will of the light source itself. Because of this, I think measuring lux at 1 meter can give false information on some of the seriously columated and far throwing systems.
We don't have perfect columation because our reflective surface is not a perfect parabola and our source of light is not from an infinitely small point, perfectly alligned with the focal point of the reflector. Most of the light produced or photons sent out comes from outside the focal point and as a result these photons are redirected by the reflector but not in columation. The further the photon source is from the focal point, the less it will be columated with photons emanating from the focal point. The greater the displacement from focal point, the greater will be the divergence of the resulting beam, I believe. This is my understanding and explaination of the 5W VS LuxIII beams when both LED's are placed in the same reflector.
Since our image (source of light or luminous die of the LED) is not a single point, we want to arrange the image so that the maximum amount of light generated is closest possible to the focal point. To my way of thinking, this is done by placing the image in the same, perpindicular to the parabolic axis, plane in which the focal point of the parabola lies. If your image size, relative to the focal length of the parabola is large (5W die in small reflector), placing the image on this plane has so much light being generated outside of the focal point that you get a beam so loose in collumation that there is a null in the center. At least this is my current interpretation. /ubbthreads/images/graemlins/smile.gif I have had some success with the 5W in placing the die below the focal point. The other means of blending or randomizing the photon paths to blurr the projection is by the orange peel surface of the reflectors where you have significant surface area that is not true to the parabolic curve. Again, I have digressed! /ubbthreads/images/graemlins/blush.gif
If you use a lambertian Luxeon, 1 or 5W with no collumating device, the rules you learned in photography will still apply.
In terms of "influencing" the lux measurement, if there is any convergence of light in the beam then I would think you could fool the lux measurement in terms of its implication of throw. If lux is measured from the source of light, IE the LED and say at one meter, you could stick a magnifying lense down close to the meter and get a good BS measurement! /ubbthreads/images/graemlins/grin.gif On a similar note, a larger diameter reflector is at a disadvantage in the 1 meter reading over a small diameter reflector because if the two had the same lux reading, the actual divergence from the large diameter reflector is less than that of the small one and its beam will hold to a tighter angle than the small one. The "cone" of light does not have its "point" at the LED but further behind it! If you want to measure the beam angle, the rim of the reflector must fall on the line used in angle measurement, if that makes any sense?? To illustrate take a ridiculous for instance of a 1' diameter reflector compared to a 1" diameter reflector and the beams being measured at 1 meter from the source of light or the front of the reflector. In either case, I believe you will agree that the lux measurements at 1 meter will be a very poor indication of what you might expect at 100 yards!! /ubbthreads/images/graemlins/icon15.gif The 1' diameter reflector would suck big time at one meter but kick A$$ at 100 meters! /ubbthreads/images/graemlins/nana.gif