Overview#

ovrtx renders six intrinsic UsdLux light types. Choose a light whose emitting shape matches the source you want to represent.

Light type	Typical use
Distant Light	Sunlight, moonlight, or another directional source that is effectively infinitely far away.
Sphere Light	A bulb or another source that emits outwards in every direction.
Rect Light	A rectangular panel or softbox that emits from one side.
Disk Light	A circular panel or downlight that emits from one side.
Cylinder Light	A fluorescent, neon, or other tubular source.
Dome Light	Image-based or constant-color environment lighting around the scene.

Light Units#

UsdLux defines inputs:intensity as the base luminance of an unnormalized light. A value of 1 at zero exposure corresponds to 1 nit (\(\mathrm{cd}/\mathrm{m}^2\)) when the light is viewed normally by a camera at exposure value 0. inputs:exposure applies a base-2 multiplier, so the scalar emission is:

\[L = \mathtt{inputs:intensity} \times 2^{\mathtt{inputs:exposure}}\]

For example, intensity 1000 at exposure 2 produces the same scalar emission as intensity 4000 at exposure 0, before color and normalization are applied.

The meaning changes when inputs:normalize is enabled:

Sphere, disk, rect, and cylinder lights divide luminance by their world-space emitting surface area. This keeps total emitted power constant when you alter their dimensions or transform scale.
A normalized distant light treats intensity at zero exposure as illuminance in lux on a surface facing the light. Its angular diameter supplies the size factor.
Dome lights ignore normalization.

Radius, width, height, and length use scene units before the prim’s transform is applied. Set metersPerUnit on the stage so those values have an unambiguous physical scale. Distant-light angle uses degrees. Color temperature uses Kelvin. Color and the diffuse and specular multipliers are unitless.

Overview#

Light Units#

Further Reading#