Study of the influence of various reflectors and scatterers on the shape of a light beam

    I am a cyclist. When you drive on public roads, you understand that there isn’t much light, and once again I sat down to read forums and articles in order to buy something else good on my steering wheel and helmet. Among other things, I came across an article by a friend known in bicycle circles, in which he recommended simple and cheap Chinese flashlights as a universal tool - equipped with various types of mounts, they can be used independently, as a bicycle headlight, and even in a bunch of different situations. One thing is bad - for different purposes, a different shape of the light beam is needed.

    This model of flashlights is a kind of designer, to which the manufacturer supplies various types of reflectors and diffusers, so I ordered everything that was available, waited for delivery, and started testing.

    So I had:

    • 4 identical flashlights. The package included smooth parabolic reflectors and plain flat glass as a diffuser.
    • Reflectors of the type orange peel (orange peel) are parabolic, but not smooth, but equipped with small, 0.5 - 1 mm, irregularities over the entire inner surface.

    • Diffusers in stock:

      • Smooth (not pictured)
      • Small (0.5 mm) hexagonal cells
      • Parallel ribs of a triangular profile
      • Large (1 mm) hexagonal cells
      • Also large cells, as the previous paragraph. At first I decided that they put two of the same - but it turned out that they give completely different light spots. after careful consideration, it became clear that they have different forms of internal recesses in the emitter:

    So, it turned out 12 options for combinations of reflectors and diffusers. I photographed the light beam that is formed from each combination and formed a summary table:

    Based on these images, we can draw the following conclusions:

    1. The best point source (as a search lamp) - is formed with a combination of a smooth parabolic reflector and without a diffuser.
    2. Paradoxically, the use of an “orange peel” type reflector has almost no effect on the light beam. Compared to the type of diffuser, its effect is minimal.
    3. The use of an orange peel reflector without a diffuser increases the angular size of the central beam by about 1.5 times.
    4. The smoothest-growing beam (with intensity growing toward the center, approximately according to the Gaussian law) is obtained by combining an orange peel reflector and a coarse-diffused diffuser. The reflector makes the distribution a little smoother. Such a bundle is suitable, for example, for mounting on a helmet during night riding in the woods.
    5. A wide beam of uniform intensity did not work out under any combination, but closest to it was a smooth diffuser with a smooth reflector. In the center, with this combination, artifacts similar to the shape of the emitting crystal are observed.
    6. And finally, the most interesting result is obtained by combining an orange peel reflector and a ribbed diffuser. This combination allows you to get a beam expanded in one plane. Such a light is ideally suited as a bicycle headlight, as it will allow you to illuminate a fairly wide angle and not blind oncoming pedestrians and drivers of other vehicles, which, given the very serious power of this flashlight, is an urgent problem.

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