Lumens, lux, and lux-second. Where are you?

lehill
April 17, 2023
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    Members 75 posts
    April 17, 2023, 5:10 p.m.
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    Wikipedia tells me the SI unit "lumen" is the power flux of a radiant source with some kind of wavelength, or color, weighting to make it relevant to human eyesight. When I buy a lightbulb in the US, the lumen rating is printed in big letters on the box.

    Lux is lumens/meter² incident on a surface. Lux-second, a derived SI unit, is the time-integrated illuminance or the time-integrated luminous flux incident on a surface.

    These, and other related SI units, seem ideal for use in photography. Why is it I only rarely* see them used even in advanced photography discussions? Am I looking in the wrong places?

    *My granddaughter's Sony W800 compact camera has a "Minimum Illumination" specification of 28 lux.

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    Team
    April 17, 2023, 5:22 p.m.
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    The problem is that photography has developed ad-hoc units. The official SI unit of exposure is the lux second. That is the unit that appears in the ISO standards that define the units used in photography officially. Scene luminance should be lux, but photographers tend to use EV₁₀₀, and then forget the 100 and call it 'EV'.
    When I've said that exposure is measured in lux seconds on photography forums I get accused of saying things only PhDs can understand.

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    Members 75 posts
    April 19, 2023, 2:23 a.m.
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    Thanks Bob. I'm sure when the camera development engineers receive a shiny new prototype sensor from the foundry they're all over it and there are lots of lumens and luxes flying around.

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    Removed user
    April 19, 2023, 7:18 p.m.
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    My experience elsewhere is that, even in an advanced discussion, correspondents are reluctant to put actual numbers to anything, thereby obviating the need for actual units - preferring instead to talk in SPV (Standard Photographic Vague).

    Nope, IMHO ...