The answer is quite simple. Snow has the highest albedo of any naturally occurring substance on Earth. Albedo is the percentage of reflectance (of light) off the surface of an object. Snow is ~ 90% reflective, which is why it is so damn bright.

What is the brightness of snow called?

Albedo is usually differentiated into two general types: normal albedo and Bond albedo. The former, also called normal reflectance, is a measure of a surface's relative brightness when illuminated and observed vertically. The normal albedo of snow, for example, is nearly 1.0, whereas that of charcoal is about 0.04.

Does snow produce light?

The colors of snow. Generally, snow and ice present us with a uniformly white appearance. This is because visible light is white. Most all of the visible light striking the snow or ice surface is reflected back without any particular preference for a single color.