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Discussion in 'Electronic Basics' started by [email protected], Jun 23, 2007.

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  1. Guest

    I have a flashlight that produces a very bright spot in the center and
    even light outside of it. The bright spot tends to hurt my eyes, so I
    was wondering if there is a type of flashlight that produces a very
    even light completely without any bright spot.

  2. kell

    kell Guest

    One of those flashlights with about a dozen leds will cast a pretty
    even light, you'll find.
  3. The bright spot is produced by the parabolic reflector
    focusing the point light source (the filament) into a
    collimated beam, the width of the reflector. The
    surrounding glow is the light from the filament that misses
    the front of the reflector and just fans out uniformly from
    the front of the filament.

    You can defuse the reflector collimated beam by adding a
    layer of frosted Scotch Magic tape to the front of the
    glass. But the flashlight will no longer throw a long
    distance beam. Leave a little of the glass uncovered if you
    want to keep a little of the long distance beam (hot spot).
  4. Ulysses

    Ulysses Guest

    I have several CCFL lights (cold cathode fluorescent lamp) that use four AA
    batteries. They produce an even light and are very reliable. The tubes
    have a life of something like 5000-25,000 hours depending upon who you ask.
    I've been using mine daily for a few years. Most of them also have a
    spotlight (halogen) bulb but heck, you could always take out the bulb if it
    bothers you. They go for a few hours on NiMh batteries and longer on

    Here's an example on ebay that also has LEDs in it. Mine don't.

    I only paid about $8 each for mine a few years ago. BTW ccfl tubes are also
    used in many laptops to illuminate the screen.
  5. Someone has already mentioned flashlights with multiple LEDs in them.
    Some time ago, from Costco, I purchased some single-LED flashlights
    with bodies made entierly out of aluminum. The single LED is quite
    bright and they use a reflector (as already mentioned) in order to
    help form a narrower beam for further reach. However, at night (very
    late, say midnight?) when I'm walking along my driveway (1/4 mile
    long, in the woods), I will often just take the reflector cover off of
    the light, exposing the LED die in the center of a flat circle. It
    casts out a very nice and even distribution of light (almost
    lambertian) that is very good at night out to 50 feet or so and covers
    the entire 180 degrees in front of me in just the optimal way for
    night walking and seeing everything around you nearly at once.

    I have done the same thing with traditional flashlights using
    incandescent bulbs with results that were very much inferior for that
    purpose. So I greatly prefer the unfocused LED light, walking my
    driveway from time to time. It provides all the right distributions
    of intensities at all the right angles away from center-line and
    without uniformity weaknesses. The incandescents I've tried have been
    kind of wan, by comparison. Admittedly, they don't have a backing
    flat reflector, so some of the light doesn't go forward when the
    reflector is removed, though. But even defocusing them doesn't really
    get nearly as good a result, so I still prefer that one LED light I
    found for this purpose.

    Another approach for flashlights where possible, is to defocus the
    beam a bit by unscrewing the cap somewhat until you get something
    close to what you are looking for. Try that, too.

  6. Jasen

    Jasen Guest

    Maglite(tm) makes a number of adjustible ones, expect to pay for quality.

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