Scene luminance has nothing to do with exposure.

The in camera histogram does not measure scene luminance. It’s affected by other things, too.

Ouch!

Tony, could you tell us what ISO was used for the shot and was any Exposure Compensation applied (if so, how much)?

From ExifTool-12.63/lib/Image/ExifTool/Exif.pm

lines 2229 and 2230:
# Wikipedia: BrightnessValue = Bv = Av + Tv - Sv
# ExifTool: LightValue = LV = Av + Tv - Sv + 5 (5 is the Sv for ISO 100 in Exif usage)

lines 4472 .. 4484:

LightValue => {
        Notes => q{
            calculated LV = 2 * log2(Aperture) - log2(ShutterSpeed) - log2(ISO/100);
            similar to exposure value but normalized to ISO 100
        },
        Require => {
            0 => 'Aperture',
            1 => 'ShutterSpeed',
            2 => 'ISO',
        },
        ValueConv => 'Image::ExifTool::Exif::CalculateLV($val[0],$val[1],$prt[2])',
        PrintConv => 'sprintf("%.1f",$val)',
    },

lines 5069 .. 5083

# Calculate LV (Light Value)
# Inputs: 0) Aperture, 1) ShutterSpeed, 2) ISO
# Returns: LV value (and converts input values to floating point if necessary)
sub CalculateLV($$$)
{
    local $_;
    # do validity checks on arguments
    return undef unless @_ >= 3;
    foreach (@_) {
        return undef unless $_ and /([+-]?(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?)/ and $1 > 0;
        $_ = $1;    # extract float from any other garbage
    }
    # (A light value of 0 is defined as f/1.0 at 1 second with ISO 100)
    return log($_[0] * $_[0] * 100 / ($_[1] * $_[2])) / log(2);
}

I know apps do show only some tags of all of them. I used exiv2.

ExifToolGUI is only for Windows or Mac. But I found another tool called exif.

With it I get one interesting info: Brightness |4,73 EV (91,05 cd/m^2).
Is that the same value as Light Value in your picture?
At least it is a metric value which is better to understand than luminance in cd/ft2) in en.wikipedia.org/wiki/APEX_system#Use_of_APEX_values_in_Exif

Still I can not get FOV or CoC or Hyperfocal Distance, which were interesting things to know too.

Edit. Iliah posted when I was writing. I guess this is the answer to my question:

Not my picture, but looking around today they are not necessarily the same.

They are also calculated values and may not necessarily be in all image EXIFs ...

The CoC is an assumption that determines the Hyperfocal distance, so if I use a CoC of .02 mm (which I do) then the hyperfocal distance increases and the DOF decreases. FOV is also based on the format used, which on many cameras is selectable and that is in the EXIF data too, but that doesn't take into account that often photos are cropped versions of the original.

ISO 450

I may have applied EC, though when using Auto-ISO I usually don't. Since it was in Manual Exposure mode I think the EC doesn't show up in the EXIF data (I can't find it here or in a couple of other files I looked at).

In Sony files the EC tag is Exif.Photo.ExposureBiasValue. Exiv2 shows it in form Exif.Photo.ExposureBiasValue SRational 1 -7/10 EV.
EC was -0.7

And Exif.Photo.ExposureBiasValue SRational 1 0 EV in a picture with no exposure correction.

Thanks Tony!

Mystery of "Light Value" solved to my satisfaction ...

LV = EV corrected to ISO100 = log2(N^2/t) - log2(450/100) = 9.34 - 2.17 = 7.17.

the very comprehensive paper i read said that using Auto Wb is used to use a histogram as a luminance meter.

www.image-engineering.de/content/library/conference_papers/before_2009/luminance_meters.pdf

Deleted

You misunderstood something. At the very least, the camera needs to be characterized first, to determine the transfer function.

[deleted]

Yup.

the article i read said exposure levels.