Lighting Design Glossary

Daylight
Sunlight
Sky Light
Ground Light

(Terms of daylighting)

Daylight encompasses all natural light that is available during the day and originates from the radiation of the sun in the visible spectrum.

Sunlight is the part of daylight that is radiated directly from the sun to the area of interest.

Sky light is the part of the daylight that is scattered and redirected by the atmosphere. It can be available together with sunlight, or alone (eg. on cloudy or overcast sky conditions).

Ground light is daylight that is reflected by surfaces below the observer (mathematically: below the plane of the horizon). This term is not very common, and is only used with this meaning in the context of very accurate lighting simulation software like Radiance.