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A lux meter

  1. Mar 5, 2015 #1

    I have a question.

    I have measured with lux meter the illuminance of the room. When in front of the photoelement I put my plastics - colourless, green, red, blue. The lux value had decreased in the same tendency - from the colourless to the smallest value of blue sample. So, can I made some conclusions about my plastics' permeability or it is impossible.
  2. jcsd
  3. Mar 5, 2015 #2

    Simon Bridge

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    Welcome to PF;
    You put a plastic something between the light meter and the light source and the reading decreases - so, yes, this tells you that the plastics are somehow blocking some light from the source.
  4. Mar 6, 2015 #3
    Is it correct:
    that I have mesuared the illuminance (lumen) in the room. After that in front of the lux meters' fotosensor I put polymer (about 5*5 cm, quite close) first colourless and after I tried others. From these results can I calculate T (clearness)- the polymers' light permeability? Value with polimer (lux) divided by room illuminace (lux)(where T is I permeatable light / I falling light). Would it be a correct valuation?

    How works a lux meter? Does it measure what is coming directly 90 degrees from the light source? Is it a problem that I have used small sample?
  5. Mar 6, 2015 #4
    Who can comment this and discuss with me?
  6. Mar 6, 2015 #5


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    There are probably several experts on this forum, but are waiting for you to provide a bit more information. I also suggest you consider a photography board as you might find even more experts to consult with.

    A little background of your own studies and what this is for would also be nice. Your post structure implies to the casual reader that you might be a non-English speaker or young. If you are Non-English, you might be ready for or expecting an in-depth explanation of your meter. If you are young, a more superficial explanation might be sufficient or all that is expected.
  7. Mar 6, 2015 #6

    Simon Bridge

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    The lux meter measured illuminance on the surface of the detector - not of the room.
    This allows you to measure the intensity, as perceived by the human eye, of the light at the place that you held the meter ... so you hold the meter close to a camera and it tells you how bright the picture is going to look. OF course you can always just use your eye.

    When you look through a colored filter, the light is dimmer ... the darker the color, the dimmer the light as perceived by the eye.
    You already know this: just hold the colored plastic to your eye and look through it to see this.
    That is all the lux meter is telling you.

    You can use this to define a "clearness" parameter for the plastics if you want.
    But it sounds like you want to measure the transparency of the plastics - is this correct?
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