Calculation for led optics.

Discussion in 'Lighting' started by Mc, 30 Apr 2012.

  1. Mc

    Mc

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    Hi all

    I'm a bit confused about something here and I think I'm not the only one.

    When working out what optics you need for an led, how would you perform the calculation. This is how I would do it but I am not sure if its correct.
    Please correct me if I'm wrong, I am just trying to understand this.
    I am not sure if I'm missing something here?


    High school maths again.:lol:
    [​IMG]
    Angle (a) is half the angle of the optic, for this example I will use a 60 degree optic so angle (a) will be 30. I then take cos(a), in this example cos30 which is 0.86 and divide (b) by it (b) is the distance from the led to the bottom of the tank, I will use 500mm for this example. This gives me (c) which is the length the light will cover at the bottom of the tank.

    (b)/cos(a)= (c) 500/0.86=581

    So the led should cover 581mm at the bottom of the tank.

    With a 80degree optic using the same equation it should cover 657mm.
     
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  3. mandarinman

    mandarinman

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    120 deg is recommended apparently
     
  4. butcherman

    butcherman Moderator MASA Contributor

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    On 1 optic is easy. How would we calculate the coverage when we overlap 5 led's? or for even more?
     
  5. Jeann1

    Jeann1

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    120? That sounds a bit to much - if you by cree LED's , most likely you will ither get 60 or 80 degree lenses.

    As far as i know, mixed them 1/1 so if you have 10 whites, 5x60 and 5x80.

    60 gives you depth and 80 gives you a broder spread.
    @butcherman can confirm
     
    Last edited: 30 Apr 2012
  6. butcherman

    butcherman Moderator MASA Contributor

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    I am not an expert, but lets look at my tank.

    It is 1.2m x 450mm x 450mm. I built 2 led uinits, 24 led's per unit 220mm x 150mm heat sink. I thus needed the each unit to cover 600mm x 450mm

    I found the following at 5 cm unlensed (ie 120 deg) the coverage was great but the intensity was not good
    I ended up using 60 deg optics and I ended up to mount them 450mm above the water (ie 900mm) above the aquarium floor (according to your calculations i should of had more that 700mm raduis)
    but i still had some low light areas.
    In the end I mixed 10 x 60 degree optics with 10 x 90 degree optics @ 450mmm above the surface of the water to get the 600mm x 450mm foot print

    Maybe someone can make sense of my findings.
     
  7. butcherman

    butcherman Moderator MASA Contributor

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    the experts say if you looking at more than 500mm you need to use 60 degree optics for the right amount of light penetration. but i think it depends alot on the concentration (proximity) of the led's in the first place.
     
    Last edited: 30 Apr 2012
  8. LCornelius

    LCornelius Moderator

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    Agree with @Jeann1 on the use of multiple lenses.
    Cree are the market leader in my opinion and a mix of 60 and 80 optics would work great.
     
    Last edited by a moderator: 26 Nov 2015
  9. butcherman

    butcherman Moderator MASA Contributor

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    my findings too.
     
  10. dallasg

    dallasg Moderator MASA Contributor

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    having researched this, i have the following to add

    you dont need optics, i have seem the illumina by vertex get 260 par at 500mm or so, if you need depth you go with 45 or 60 deg optics, and 70/80 for a tank shallower than 600.

    now you calcs are right, it will cover that but the visibile light is not what we want, we want PUR so the disappation from the focal center of the beam causes the light to get weeker as it spreads, and quite substantially, what tank u looking at using this on?
     
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  11. mandarinman

    mandarinman

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    Learning as i go!
     
  12. dallasg

    dallasg Moderator MASA Contributor

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    dont we all
     
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  13. Mc

    Mc Thread Starter

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    Thanks for all the replies its alway good to learn something new.
    I have 60 degree optics on my tank and they don't seem to be too focused, but they are quite well spread out over my tank.

    One of the reasons I ask this is because I am looking adding a few more leds and was thinking of going with the 80 degree optics.

    This is what I was wondering about, so the pur would be weaker toward the edges of the spread.
    So even though it seem to be spread out to the eye, the really useful light actually isn't
    Do you know how much it get weaker by?
    You say optics aren't needed does this apply to leds with a 110 degree angle?
     
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