Lighting engineers often refer to their area of expertise as the "science of lux and lumen". The two terms are units of measurement for key lighting variables.

Lux (lx) is the unit of measurement of illuminance. It indicates how much light – or more specifically how much luminous flux – falls on a given surface. Measurements are performed with a luxmeter. In an office, for example, at least 500 lux is required for desk work.

Luminous flux is measured in lumens (lm) and describes the visible light radiating from a lamp in all directions. Two examples: an incandescent lamp has 1,400 lumens, a double-based halogen lamp as many as 44,000 lumens. The luminous flux ratings of lamps are found in manufacturers' product lists.