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Thread: 0.25 Lux distance

  1. #1
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    Default 0.25 Lux distance

    Hello,

    I would like to calculate the 0.25 lux distance of several laser devices. I have the power of each device, wavelength, beam diameter. Do you have any idea on the formula to use?

    Thanks a lot !

  2. #2
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    I'm not not familiar with the term 0,25 lux distance. Can you explain in what context it is used ?
    If it is safety related, please note that special rules apply.
    Lasers are not ordinairy leds.

    Since you mention distance, I assume that you need divergence parameters too.
    If you're new to lasersafety I highly recommend the apps :
    Laser safety
    laserNOHD.

  3. #3
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    Thanks for your answer.

    In fact, I need to evaluate the lux power of a laser device at a given distance. For example : which will be the lux power at 100meters from the laser device? (I will have the beam diameter, divergence, power & wavelength).

  4. #4
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    What part of the calculation is troubling you, and what did not?

    Lux power is a misnomer, its unit is not W or J/Sec but lm/m2 or cdĚsr/m2

    First you will have to calculate the lumen equivalent output by the laser.
    Next, calculate the spotsize (round/square?) at the given distance.
    Then the illuminance comes out easy.

  5. #5
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    Thanks Bart, I just managed to calculate the lm conversion, however it seems that there are two types of lm conversion: photopic and scotopic (for ex here: http://hyperphysics.phy-astr.gsu.edu...ficacy.html#c1). Should I take the photopic or scotopic conversion ?

    Second question : one of the devices has a beam shape of 2mm x 5mm, and divergence of 1.5mRad. What will be the spot dimension at 100m for ex? (what is the formula?)

  6. #6
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    Photopic.

    2x5 mm is the nearfield beamshape. To accurately determine the farfield beamshape, you need both the fast-axis and slow-axis divergence. It is simple geometry.

    Rule of thumb is 10cm increase per 100 meter per mRad.

    Keep in mind that many manufacturers give very optimistic power and divergence figures. And usually they don't define how divergence is determined at all.
    When safety is concerned; DO take measurements.
    Last edited by -bart-; 07-24-2013 at 01:20.

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