Re: In theory what type of reflector has more thr
Note: the following ramblings are based upon the knowlede of a person who likes flashlights, but knows more about math than lights...
In theory, the parabola is great. If the bulb is placed at the "focus" of the parabola, all light rays which hit the reflector will go straight forward. In theory, you will get a perfect, smooth, even beam which will still be well-focused at 100 yards. Any light which goes toward the reflector will become part of the "spot," and any light which goes forward becomes part of the "spill." So this type of light will always have some spill. If you want more efficiency, you have to make your reflector larger, but at some point you will have to add a lot of reflector in order to get just a little extra light.
The problem is that "in theory" means having a bulb which glows brightly at one point. The problem is that bulbs have a long glowing piece of tungsten wire. Only ONE point of the wire will be in focus, and the rest of the fillament will be out of focus. This is the reason for artifacts in the beam, and why you use a faceted reflector to try to remove those artifacts. But the more you deviate from a parabola, the more you loose throw. On my Tigerlight (my best light), I can actually see the little spiral shape of the fillament in the beam.
The properties of an ellipse is that any light emitted at one focus point will be directed exactly toward the other focus point (A parabola is simply an ellipse with the other focus point infinitely far away). An elipse would be great for specific applications, such as knowing already how far away your target is. I would not choose one for general use, though. You also have the same "a bulb is not a pinpoint-source-of-light" problem as a parabolic reflector.
The spherical with a lens is a different animal entirely. The point is that you have the lens arranged so that any photons leaving the focal point and going to the lens will be focused (probably into a nice parallel beam). The problem is that, more than half of all light will NOT go through the lens. So the solution is to put a spherical reflector around the bulb. Any photons which go "backwards" are then reflected forwards, where they pass very near the bulb, and then hit the lens. This type of light can indeed be very nice and bright (in theory) if you use a standard lens (like you would find in a camera), and if you have a pinpoint source of light. I believe that this is the type of headlight used in some sports cars (but I could be wrong). Fresnel lenses are a compromise because they are not distortion free, but they are a lot thinner and lighter (and cheaper). Unfortunately, they might degrade the quality of the beam. This type of setup also has little to no spill light.
