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Thread: Perceived Increase In Brightness

  1. #1
    BVH's Avatar
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    Default Perceived Increase In Brightness

    I've read posts here dealing with how much more power or Watts it takes for a light to appear twice as bright. I've had a chance to do some experimenting with a 300 Watt short arc bulb today. Since buying the Megarays which use a 175 Watt Cermax sealed beam short arc bulb, I've bought a programmable (via a keypad and not changeable once running) 300 Watt and two programmable (changeable from 100 Watts to 500 Watts when running) 500 Watt short arc bench power supplies with ignitors built-in. For fun, I played with the 300 Watt bulb today running off of one of the 500 Watt supplies. In order for my eye to detect the slightest decrease in brightness, I had to crank down power from 290 Watts to about 250 Watts in one swift motion. So it took a 15% decrease in power to see anything. I didn't go lower than 235 Watts because I don't know if it might be detrimental to the bulb. Nothing Earth-shattering, just some data to help understand the relationship between more power and more light - or in this case, the reverse.
    WWII 60" Anti Aircraft Carbon Arc (Sold), Short Arcs: 1.6KW NightSun, 1KW VSS-3A, .8KW TrakkaBeam, 600 Watt M-134 Gun Light, 500 Watt X-500-14s, 500 Watt Starburst, 300 Watt Locators, Megaray, 150 Watt Set Beam & Communicator, Maxabeam Gen3, LarryK14@52V

  2. #2
    Flashaholic* larryk's Avatar
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    Default Re: Perceived Increase In Brightness

    I understand what you mean by perceived increase In brightness. In the old days I had a Colmann spotlight using a 100 watt incandescent bulb. I had the light plugged into the cigarette lighter of my car. It did not appear that much brighter with the engine running (12 volt vs. around 13.5 volt) until an ex member took a photo of the difference.
    Collins Dynamics CD-12, CD-12 Magnum, Microfire Warrior, Iluminator HID, Costco HID, ,Maxabeam, Polarian Helios, RayzorLite ,BarnBurner,and a bunch of small lights.

  3. #3

    Default Re: Perceived Increase In Brightness

    Its typically easier to see side by side/one then the other...rather than just walking out one night, being shown a beam, ad being asked what its brightness is relative to something you saw the night before, etc.

    If you have a light with infinitely variable brightness/ramping, etc...you can tell its getting brighter/dimmer very easily...but not if you close your eyes, someone else turns the dial to a new, nearby brightness, and asks you to open your eyes and tell them if they made it a smidge lighter or dimmer.

    Your 15% estimate is probably about spot on for those conditions...given the short delay.

    Its a lot more accurate than the dogma that "a light has to be twice as bright to perceive the difference".


  4. #4
    *Flashaholic* Patriot's Avatar
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    Default Re: Perceived Increase In Brightness

    Good info Bob. I really appreciate this type of first hand data!

    I remember when I had the PH40 and PH50 at the same time. Sometimes while testing them at some dark location I'd get the two mixed up when viewing them alone. It wasn't until they were switched on side by side that I could see which was which. You had to drop a whole 40W to see the change but by percentage, my experience and yours is somewhat similar.

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