The likely word is the transposition contrast (comparing differences, or brightness range).

The guns are generally rated on caiber or guage. The flares may be rated on range, type, brightness, color, etc.

Common types of radiation pyrometers include brightness, color, and total-radiation pyrometers. Of particular importance is the brightness pyrometer, which provides the highest accuracy of temperature measurements in the range from 103 to 104 °K.Total-radiation pyrometers can be used to measure temperatures beginning at 200°C.

An apparent brightness is the brightness of a star as measured by an observer.

Absolute Brightness: How bright a star appears at a certain distance.

Apparent Brightness: The brightness of a star as seen from Earth.