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Thread: Light Metering in Snowy Conditions

  1. #1
    Join Date
    Dec 2017
    Location
    Alaska, USA
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    9

    Light Metering in Snowy Conditions

    I need to measure the available light at a gate to make sure it meets regulations here. However, the ground is snow covered right now. I can not wait till it melts because this needs to be part of a summer project, going out for bid in advance. Also, we have a lot more darkness now than we do once the snow melts, so it would be easier (time wise) to measure now.

    Does anyone know how much of a difference the snow makes when using a light meter? Is there a standard way to compensate for it?
    (I tried internet searches, but was only able to find information for photography light metering in the snow... how to adjust the camera, etc.)
    The area is very flat with no nearby trees, if that makes a difference. I need to measure the light at ground level.

    If the available lighting does not provide enough light, I will have add additional lights to the project...

    Thanks!

  2. #2
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    18,748
    What kind of light meter are you using?
    The standard for lighting for egress, etc. involves the light coming downward onto a horizontal plane. If the light meter is a direct incoming light meter or has a half-spherical collecting dome the presence of snow should not make any difference in the reading.

    Above the surface of the snow or in a fairly wide shoveled area should be a perfectly good measurement. Ground level does not mean digging a small hole in the snow.

  3. #3
    Join Date
    Dec 2017
    Location
    Alaska, USA
    Posts
    9
    The light meter has a half spherical collecting dome. I suspected with it sitting horizontal on the snow, facing up, the snow would not make a large difference in the reading. It is good to get a confirmation of that.

    The snow would only really make a difference if I were doing a vertical reading, or if it were actively snowing, right?

    Thanks GoldDigger!

  4. #4
    Join Date
    Mar 2003
    Location
    New York
    Posts
    810
    Go to harbor freight get a movers blanked throw it on the ground where your taking a reading, no snow.

  5. #5
    Join Date
    Jun 2003
    Posts
    6,828
    What kind of light level are you looking for?

    Above 1FC, or fractions of a FC?

    Cloudy days with snow on the ground can look really bright (especially if there is a car lot nearby - it can almost seem like daylight). But I'll be the reflected light is probably less than it seems to be, and I doubt it would have much of an effect for any readings much larger than 1 FC. And as Golddigger mentioned, the meter shouldn't be measuring light reflected back up from below it.

    I do like the blanket idea, and you could even use a large cardboard box to block any light coming from the side. You might compare a couple of readings with the meter just above the snow, and with a blanket or cardboard box blocking reflected light, and see if they make a difference.

  6. #6
    Join Date
    Dec 2007
    Location
    NE Nebraska
    Posts
    34,704
    next to a building, you may get light reflected off the snow..then off the building.

    Out here in the country when it is dark it is dark snow or no snow. But even a quarter moon makes a huge difference in lighting things up when there is snow vs no snow.

  7. #7
    Join Date
    Dec 2017
    Location
    Alaska, USA
    Posts
    9
    Thanks guys! I did confirm with a professional photographer that I should be ok to get an accurate light reading, having the photometer on the ground facing up.

    FYI, I need a 5 FC reading.

    However, I also like the blanket idea and will use it. It will make the wary customer feel better. He was very concerned about the snow changing the reading.

    Luckily we've got a nice clear sky this morning so I don't have to worry about the clouds, etc.

    Cheers,
    Debbie

  8. #8
    Join Date
    Jul 2015
    Location
    Soldotna, AK, USA
    Posts
    88
    Quote Originally Posted by deb4523 View Post
    Thanks guys! I did confirm with a professional photographer that I should be ok to get an accurate light reading, having the photometer on the ground facing up.

    FYI, I need a 5 FC reading.

    However, I also like the blanket idea and will use it. It will make the wary customer feel better. He was very concerned about the snow changing the reading.

    Luckily we've got a nice clear sky this morning so I don't have to worry about the clouds, etc.

    Cheers,
    Debbie
    Parking lot/area? Have him sand it if hes still worried.

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