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Thread: White LED experiment

  1. #57
    Hello, I must be going... Not a Number's Avatar
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    Lenses do not ultimately negate the Inverse Square Law. What they do is alter the virtual position of the light source (opposed to the physical location). Measurements calculated from the virtual position will obey the Inverse Square Law.

    A convex lens which focuses the light essentially moves the virtual position of the light source to the focal point in front of the lens.

    Although this article uses a concave Fresnel lens in the illustration it doesn't take much imagination to substitute a convex lens.
    http://www.portraitlighting.net/inversesquare_law.htm
    Grand Hotel... always the same. People come, people go. Nothing ever happens.

  2. #58
    Av8tor1's Avatar
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    Hehehehe I was looking for ya Warren

    I agree with you, but that is exactly my point... In your ref it makes this statement under exceptions: Sources that use optical or physical means to collimate light will not follow the inverse-square relationship, at least when based on their physical location.

    Typically, decreases in light intensity as it relates to the distance from the physical location of the source is the application that we normally apply it to.

    I'm just stating the same thing... ummm I think
    In this application the auxiliary optics effectively collimate the light to some degree, therefore we cannot apply it as we normally would.
    (In theory, if the light beams were perfectly parallel wouldn't its focal point be infinity? e.g., Lasers)

    So doubling the distance would not have the same effect
    Last edited by Av8tor1; 06-13-2010 at 07:10 PM.

  3. #59
    mobile's Avatar
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    Quote Originally Posted by Av8tor1 View Post
    A generic regulated Apple laptop power supply on Ebay is 24vdc and about 12$
    The heatsink is a common PC processor heatsink, buy those anywhere on the cheap... few dollars
    Av,

    I hadn't realised that you used a DC supply to feed the buckpack. Is there a reason why you didn't use an LED driving which can accept a 110Vac input, such as the one linked below?

    http://www.stadiumpower.co.uk/upload...C_05112008.pdf

  4. #60
    Av8tor1's Avatar
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    Good question,

    I already have quite a few DC power supplies. With this in mind, it was cheaper to go with a low voltage driver module. Especially since I wasn't sure this would even work well.
    Buckpack also has models with a 110vac input and there are other brands that do as well.

    With an eventual goal of a HL/UHL centerpiece type setup with a 12v peliter it made even more sense. One of the power supplies I have is a nice Astron 12amp that I will probably use to drive the entire setup. Now I will only have two low voltage wires running to the setup.

    Had I not had the power supplies and peltier to deal with, I would have gone with a 110vac driver module.....hmmm maybe LOL, there would still be the fans to deal with

    Av

  5. #61
    Hello, I must be going... Not a Number's Avatar
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    The Inverse Square Law applies pretty much only to single point or isotropic energy sources. LASER energy is highly directional and moves in near parallel paths. There is some degree of divergence in LASERs. Researchers relied on some of that divergence in hitting the LASER target experiment left on the moon during the Apollo missions. You could imagine how much more difficult it would be to try to hit a small object with a very tiny beam at such distances and speeds.

    So the Inverse Square Law:

    If a point source is radiating energy in three dimensions and there is no energy lost to the medium, then the intensity decreases in proportion to distance from the object squared. This is due to physics and geometry. Physically, conservation of energy applies.

    So light from a single point source travels outward in a sphere so as the distance from the source increases so does the surface area of the sphere. So in a sense the density of the photons would decrease as the surface area increases. Imagine a balloon painted with polka dots: as you inflate the balloon the number of dots remain constant but the space between the center of the dots increases also. This is not a perfect example - you would have to imagine that the size of the dots remain constant also.

    A practical demonstration of this would be to take a conventional light source such as an ordinary incandescent light bulb. Cut a circular hole in a card opaque enough to block the light from the bulb. Keeping the distance constant between the light source and bulb observe the diameter of the "spot" of light passing through the hole on a card at various distances from the light source. The area of the "spot" should increase or decrease in accordance to the Inverse Square Law. Notice also that the "brightness" of the spot increases or decreases also. See the diagrams here.

    The diameter of a laser beam for all intents and purposes in the distances involved for indoor plant growing will remain constant - thus the Inverse Square Law would not apply.
    Grand Hotel... always the same. People come, people go. Nothing ever happens.

  6. #62
    Av8tor1's Avatar
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    I totally agree, its the size of the sphere doubling is key.... and this relationship with the source can be affected by optics
    The balloon example reminds me of an method of demonstrating how the universe can expand in all directions from any one point

    Nice

    I'm definitely not expert in these matters but here is my logic. In this application, the distribution of energy does not remain constant over the sphere as the distance from source is increased. As a result of the optics a portion of the light waves are collimated to some degree. This portion will not distribute as much as the uncollimated portion would. Hence, the power distribution is not equal and constant as a function of distance from source. However, the inverse square law assumes that the energy is distributed evenly and that this distribution ratio is constant over the sphere even as the size of the sphere increases.

    LOL, but i could be full of it too
    Last edited by Av8tor1; 06-14-2010 at 06:10 PM. Reason: hehehe clarification

  7. #63
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    Additional communications with Luxeon, I asked them to evaluate the project:

    ....I had a quick look at the thread and you seem to have a pretty good handle on how to use these LEDs. The most important element of using these LEDs is the cooling - and it would appear that you have that taken care of using the CPU heat sink. However I would still be inclined to check the running temperature of the LED if you can. If you have access to a very small thermocouple and temperature meter, then measure the temperature right on the base next to the LED. It should not be more than 80C - tops. Lower is better. 40C would be ideal if you can get it down that low. Heat destroys more LEDs over the long run than anything else. And the problem is it does not happen right away. It is a very slow degeneration process that causes the LED to slowly grow more dimmer over time.

    Now while my temps are already close to 40C with passive cooling, I guess it would be prudent to go ahead and use Low Cfm/RPM/dB fans and stay at the 700ma current level.

    Av

  8. #64
    Your one and only pest! Ant's Avatar
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    Wow, that is pretty darn bright... I thought those LED mini-flash lights were bright to. I would love to see an update on the ping!

    So, to even begin to understand the terms that you used to describe the use of these lights, where do I go? lol Probably will be way out of my price range for a while.

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