The term 'measure of brightness' refers to the units used to measure the intensity of light. Lumen (5 letters) is a unit of luminous flux, which is the total amount of visible light emitted by a source. Candela (7 letters) is a unit of luminous intensity, which is the amount of light emitted in a particular direction. Lux (3 letters) is a unit of illuminance, which is the amount of light that falls on a surface. IQTest (6 letters) is not related to the term 'measure of brightness' and is instead a type of intelligence test.