Contrast

Not to get too technical on you, but contrast is how you judge a scope's ability to manage light. And, if a scope can't manage light, you might as well go bowling.

Contrast is enhanced by resolution, which has to do with producing a crisp, finely detailed image. Contrast is also enhanced by light transmission, a parameter that is affected by the number of glass or mirrored surfaces, the absorption of light in the glass materials, and the quality of the anti-reflective and mirrored coatings.

As we all know, glare is the enemy of contrast. Glare is the stray light that reflects off internal parts of a scope and sneaks into the field-of-view. Glare also diminishes detail and color quality of the image. Needless to say, you should look for a scope that has more contrast and less glare.