Dusk under haze

An environment light source that implements a simple analytical physical model for terrestial daylight under clear skies. The sky model is based on A Practical Analytic Model for Daylight by A.J. Preetham, Peter Shirley, and Brian Smits. The solar disk model is adapted from H.C. Hottel's A Simple Model for Estimating the Transmittance of Direct Solar Radiation Through Clear Atmospheres, with parameters curve fitted for turbidity from physical data and a simple limb darkening model.

In typical use you will create an envsphere as the geometry and attach this as a light source shader to it. To make the sky directly visible to the camera, add the PxrLightEmission material as the Bxdf as well.



Exposure specifies the intensity of the environment light as a power of 2. Increasing the intensity by 1 will double the energy emitted by the light source. A value of 0 produces an intensity of 1, -1 produces .5.

The light intensity is computed using physical units which are typically 100.000 times too intense for regular RGB rendering. We scale it internally by 1e-e5 to generate pleasing illumination levels.

The intensity parameter in the Advanced section can also be used to lineary scale the light intensity.

RIB: float exposure
Default: 0

Sun Parameters

Sun Tint

Tweak the sun's contribution and color. The default, white, gives results based on measured physical values.

RIB: color sunTint
Default: 1.0 1.0 1.0

Sun Size

Scale the apparent size of the sun in the sky. Leave at 1 for a realistic sun size with an 0.55 degree angular diameter.

RIB: float sunSize
Default: 1.0


The sun direction can either be specified as a vector or using the heliodon.

RIB: float method
Default: 0 (vector)


The apparent direction towards the center of the sun. The zenith is at +Y (for noon light) and the horizon is in the XZ plane (for sunrise/set). Note that the Y component must non-negative.

RIB: vector direction
Default: 0.1 1.0 0.1



Month of the year, 1 through 12.

RIB: float month
Default: 11


Day of the month, 1 through 31.

RIB: float day
Default: 20


Four digit year.

RIB: float year
Default: 2014


Hours since midnight, local standard time. May be fractional to include minutes and seconds. If daylight saving time is in effect, subtract 1 to correct to standard time.

RIB: float hour
Default: 14.633333


Standard time zone offset from GMT/UTC in hours. Positive for east, negative for west. For example, this would be -8 for Pacific time.

RIB: float zone
Default: -8


Latitude in degrees. Positive for north, negative for south. Ranges from -90 to +90 degrees.

RIB: float latitude
Default: 47.601903


Longitude in degrees. Positive for east, negative for west. Ranges from -180 to 180 degrees.

RIB: float longitude
Default: -122.331817

Sky Parameters


The turbidity of the sky. The lower limit of the model is 1.7 for an exceptionally clear sky, and 10, for an inversion, is the upper limit.

RIB: float haziness
Default: 2.0

Sky Tint

Tweak the sky's contribution and color. The default, white, gives results based on measured physical values.

RIB: color skyTint
Default: 1.0 1.0 1.0

Components Weights

Specular Contribution

Scale the specular contribution of this light.

RIB: color specAmount
Default: | 1.0 1.0 1.0 |

Diffuse Contribution

Scale the diffuse contribution of this light.

RIB: color diffAmount
Default: | 1.0 1.0 1.0 |


Light sampling is automatic, but you may occasionally have to override the allocated sample budgets to clean up noise in direct lighting.

Fixed Sample Count

Override the automatic sample allocation and use a fixed number instead. Negative values disable this feature.

RIB: float fixedSampleCount
Default: -1


Re-balance the automatic sample allocation. An importance of 2 will allocate twice the regular sample budget to this light.

This method is often preferable to Fixed Sample Count, as it only biases the automatic estimates.

RIB: float importance
Default: 1.0


You can connect portals, blockers and gobos here.


Enable Shadows

Enable ray-traced shadows.

RIB: float enableShadows
Default: 1

Shadow Color

The color of the shadows cast by emitted light.

RIB: color shadowColor
Default: | 0 0 0 |

Adaptive Shadows

Adaptively sample the lights shadows.

Conservative mode will trace a larger percentage of the shadow rays, which will result in less acceleration, but potentially higher quality shadows.

Aggressive will trace fewer rays, which can result in more significant speedups.

RIB: float adaptiveShadows
Default: 1

Shadow Max Distance

Limits the shadow distance. Any value smaller or equal to 0.0 will be ignored and the shadow distance will be unlimited. Defaults to -1 : unlimited shadow distance. Can be used to optimize shadow rays in very large scenes but may introduce artefacts if set too short. Use a small value with a white environment light to achieve a short-range ambient-occlusion look.

RIB: float shadowMaxDist
Default: -1

Shadow Trace Bias

Ray tracing bias for shadow computations. -1 uses the automatically computed bias value.

RIB: float shadowTraceBias
Default: -1

Shadow Subset

Set of geometry to consider for traced shadow intersection.

RIB: string shadowSubset
Default: ""

Don't Trace Subset

Set of geometry to ignore for traced shadow intersection.
RIB: string shadowExcludeSubset
Default: ""

Advanced Parameters

Light Group

Specify the group membership used for per-light AOVs.

RIB: string __group
Default: "environment"
Note: __group is a special parameter directly used by the lighting services.


Scales the contribution of this light.

RIB: float intensity
Default: 1.0


RenderMan for Maya includes useful presets for specific times of day.


The Magic Hour (Early Morning)


Late Morning


High Noon


Late Afternoon