Physical light units
HDRP uses Physical Light Units (PLU) for its lighting. These units are based on real-life light measurements, like those you see on light bulb packaging or a photographic light meter. Note that for lights to behave properly when using PLU, you need to respect HDRP unit convention (1 Unity unit equals 1 meter).
The base unit of luminous intensity in the International System of Units. For reference, a common wax candle emits light with a luminous intensity of roughly 1 candela.
The unit of luminous flux. Describes the total amount of visible light that a light source emits in all directions. When you use this unit, the amount of visible light is independent of the source's size meaning the illumination level of a Scene does not change depending on the size of a light source. However, highlights that a light source produces dim as the area of the light source increases. This is because the same power is spread across a larger area.
Lux (lumen per square meter):
Nits (candela per square meter):
The unit of luminance. Describes the surface power of a visible light source. When you use this unit, the overall power of a light source depends the size of the light source, meaning the the illumination level of a Scene changes depending on the size of the light source. Highlights that a light source produces conserve their intensity regardless of the size of the surface.
A light source that emits 1 candela of luminous intensity onto an area of 1 square meter has a luminance of 1 candela per square meter.
Exposure value (EV):
A value that represents a combination of a camera's shutter speed and f-number. It is essentially a measurement of exposure such that all combinations of shutter speed and f-number that yield the same level of exposure have the same EV. HDRP Lights can use EV100, which is EV with a 100 International Standards Organisation (ISO) film.
Light measurements from natural sources in different conditions:
|Illuminance (lux)||Natural light level|
|120 000||Very bright sunlight.|
|110 000||Bright sunlight.|
|20 000||Blue sky at midday.|
|1 000 - 2 000||Overcast sky at midday.|
|< 1||Moonlight with a clear night sky.|
|0.002||Starry night without moonlight. Includes airglow.|
Approximate light measurements from artificial sources:
|Luminous flux (lumen)||Source|
|< 100||Small decorative light, such as a small LED lamp.|
|200 - 300||Decorative lamp, such as a lamp that does not provide the main lighting for a bright room.|
|400 - 800||Ceiling lamp for a regular room.|
|800 - 1 200||Ceiling lamp for a large brightly lit room.|
|1 000 - 40 000||Bright street light.|
Architects use these approximate values as a guide when designing rooms and buildings for functional use:
|Illuminance (lux)||Room type|
|150 - 300||Bedroom.|
|300 - 500||Classroom.|
|300 - 750||Kitchen.|
|300 - 500||Kitchen Counter or Office.|
|100 - 300||Bathroom.|
|750 lux - 1 000||Supermarket.|
|30||City street at night.|
For more examples of indoor light levels see Archtoolbox’s web page on Recommended Lighting Levels in Buildings.
Lighting and exposure diagram