Luminance is the density of luminous intensity in a given direction and falls within a given solid angle.

It is measured in cd/m².

Luminance is often used to characterize the emission from a diffuse surface. It indicates how much luminous power will be perceived by eye when viewing the surface from a particular angle. Luminance remains the same regardless of the distance from the light source.

Illuminance is the density of photons which fall within a given surface area. It is measured in lux, or lumens/m².

Illuminance can be measured with a lux meter. For a given light source, the closer to a light source the illuminated area is, the higher the Illuminance value.

Illuminance is used in lighting applications to measure the amount of light reaching an object such as a wall.

The illuminance will decrease if the total area illuminated is increased without changing the intensity of the light source, although the luminance intensity of the light source stays the same.

Fusion Optix diffusers preserve the total lumens and change the illumination profile by redirecting photons from a narrow to a wide angle.

The measure of the wavelength-weighted power emitted by a light source per unit solid angle. The units of luminous intensity are lumens/steradinn.

Luminous intensity is related to the color of the light. If two sources generated the same number of photons (radiant flux)- one was UV (non-visible light) and the other source was white- the white light would have a higher luminous intensity. It's weighted by the sensitivity of the eye. High luminous intensity looks very bright to the human eye.

Luminous intensity is often used to measure the angular output from light fixtures.

Typically, luminous intensity distribution profiles are shown in photometric plots for light fixtures. Fusion Optix Diffusers can change the profile to achieve virtually any desired angular profile.