1 Is there a physical unit to quantitatively describe the softness of light? Is there an instrument to measure the softness of light?

The physical units of detection light mainly include brightness, illuminance, color layer, contrast and so on.

Softness and glare are subjective feelings. There is no unit to describe it. Maybe in the future, it will be just like the speech intelligibility rating (mos).

For example, two objects emit the same amount of light, and the one with small surface area is more dazzling.

It's dazzling to turn off the lights at night and look at the screen of the mobile phone. You can't even see clearly in the sun.