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Before 4.24, the only measurement you could get was luminance(cd/m²) through the Pixel Inspector. Illuminance(Lux) and Exposure Value(EV) are easily calculated from one another, but I got tired of doing the math every time I tweaked lighting.
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Luminance alone is not a reliable unit for lighting because it’s a measurement of emittance. Typical real world measurements are uncommon and vary because they take the albedo AND lighting into account. It’s better suited for emissives(skies, fog, FX, etc).
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Illuminance on the other hand is the total amount of light hitting a surface. You can get measurements from a cheap meter/smartphone(yrmv) and there are numerous recommendations and known values you can compare to. Sounds like PBR right?
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An illuminance value you see in a chart doesn’t mean light intensity. Unless specified, it includes ALL light hitting the surface. With illuminance, the end result is more important(in games) than how you got there. It could be 1 light or 100 ...
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… and this is important because lumens/candelas aren’t reliable intensities either, at least as far as specs go. There’s mislabeling of true outputs, radiation patterns depending on the bulb, light fixtures/optics to account for, depreciation, etc.
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Exposure Value(EV) is a number that represents exposure through shutter speed and fstop in that any combination that equals the same exposure will also be the same EV, standardized with ISO100 but there are workarounds. Like illuminance, there are known use cases for EV.
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In 4.24, the Eye Adaptation debug was updated to show averaged luminance and illuminance based on a small area in the center of the viewport. I added EV for 4.24 and 4.25 and it should be in 4.26. This is a MUCH easier way of measuring.
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In order to get proper illuminance with either method, you need to measure a flat surface(usually horizontal) with a pure white albedo(because it affects luminance, remember?) and no specular just to remove any possibility of measuring reflections.
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If you measured with the Pixel Inspector, you can use the widget to convert your luminance and adjust as necessary. Or you could input your target illuminance and light to the provided luminance value without having to input a number every time.
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The widget provides a shutter speed or fstop under the assumption you’re using ISO100. The inputs are industry standards in half-stops for simplicity. Every other option is double the ISO, or double the exposure. Outputs are true values, not the industry ones.
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If you don’t need the manual settings or EV usages, the viewmode is definitely the way to go. But hopefully the widget is still helpful for those stuck between 4.22 and 4.24. I would have done things a little differently but there’s some formatting quirks I couldn’t work around👍🏼
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