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Daylight simulations are useful when you want a quick and easy s= etup for exterior lighting or maybe some look development time but you don'= t have an HDRI for the PxrDome= Light available. The simplicity and realism make this light a favo= rite for artists.
An environment light that uses a simple physical model for terrestrial d= aylight under clear or hazy skies. The sky model is based on A Practical Analytic= Model for Daylight by A.J. Preetham, Peter Shirley, and Brian Smi= ts. The solar disk model is adapted from H.C. Hottel's A Simple Mo= del for Estimating the Transmittance of Direct Solar Radiation Through Clea= r Atmospheres, with parameters curve fitted for turbidity from physica= l data and a simple limb darkening model.
You will see mention of "non-physical" controls. These controls are desi= gned to help artists make art-directed imagery by ignoring certain laws of = physics we usually simulate.
Intensity
Scales the contribution of this light linearly.
Exposure
Specifies the exposure of the area= light as a power of 2. Increasing the exposure by 1 will double the energy= emitted by the light source. A value of 0 produces an intensity = of 1 at the source, -1 produces 0.5. You may wonder why you might use = Exposure , a= nd the answer is that real world lighting has high energies and typical exp= osures are low values while you may have to type a really large number for = equivalent Intensity . This is also comfortable to artists familiar with photograp= hic measurements.
Direction
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 (f= or sunrise/sunset). Note that the Y component must non-negative. Ignored if= a month is given. In some DCC applications, like Maya for example, you can= manually alter the Sun direction using a manipulator in the viewport (pres= s 't' with the Daylight icon selected in the viewport.)
Haziness
The turbidity of the sky. The lower limit of the model is 1.7 for an exc= eptionally clear sky, and 10, for an inversion, is the upper limit.
Sky Tint
Tweak the sky's contribution and color. The default, white, gives result= s based on measured physical values. You may be able to create some interes= ting alien skies this way. Setting this to black removes the sky contributi= on shown in the first image.
Sun Tint
Tweak the sun's contribution and color. The default, white, gives result= s based on measured physical values. Setting this to black removes the sun = contribution like the first image (in case you want to create your own).
Sun Size
Scale the apparent size of the sun in the sky. Leave at 1 for a realisti= c sun size with an 0.55 degree angular diameter. At 0.1 you'll barely notic= e that the sun's contribution has decreased. Notice that at 80.0 we have a = very large sun in the sky that casts softer shadows since the light size ha= s increased diameter.
Ground Mode
This menu allows the user to change the appearance and effect of the vir= tual ground plane. The Legacy Mode operates as always. Horizon Clamping pro= vides a better simulation of the virtual ground mode with a blurred horizon= . Diffuse Ground allows the user to color an infinite virtual ground plane.=
Ground Color
Use this color as the rendered ground color. This is not texturable and = does not accept shadows.
Month
Month of the year, 1 through 12. The default, use direction, me= ans to use the explicitly given sun direction instead of automatically comp= uting it.
Day
Day of the month, 1 through 31. This is ignored if the month is set to <= em>use direction.
Year
Four digit year. This is ignored if the month is set to use directio= n.
Hour
Hours since midnight, local standard time. May be fractional to include = minutes and seconds. If daylight saving time is in effect, subtract 1 to co= rrect to standard time. This is ignored if the month is set to use dire= ction.
Zone
Standard time zone offset from GMT/UTC in hours. Positive for east, nega= tive for west. For example, this would be -8 for Pacific time. This i= s ignored if the month is set to use direction.
Latitude
Latitude in degrees. Positive for north, negative for south. Ranges from= -90 to +90 degrees. This is ignored if the month is set to use directi= on.
Longitude
Longitude in degrees. Positive for east, negative for west. Ranges from = -180 to 180 degrees. This is ignored if the month is set to use directi= on.
Specular Amount
Amount of specular light that is emitted. This is a non-physical co= ntrol. You could use a light with Specular Amount 0.0 to act purely as a so= urce of diffuse light for your scene objects and avoid adding highlights.= p>
Diffuse Amount
Amount of diffuse light that is emitted. This is a non-physical control.= You could use a light with Diffuse Amount 0.0 to act purely as a source of= highlights for your scene objects.
All shadow parameters will be igno= red if the light's Trace Light Paths is enabled in Advanced. The below optio= ns are all non-physical controls when used out of their default state. If&n= bsp; Trace Light Paths is enabled then their physical nature is enforced.= p>
Enable Shadows
Enable raytraced shadows. Below is= on (default) and off.
Shadow Color
The color of the shadows cast by e= mitted light.
.0 0.0 0.0
Shadow Max Distance
The maximum distance of the shadow= starting from the position of the point being shaded. -1.0 is unset which = will use the distance between the point being shaded and the point on the l= ight. You may use this control to artificially reduce the distance shadows = are cast. This may also increase render speed by not calculating shadows ou= tside this distance. Here it's used to remove the shadow off the back wall = from the sunlight.
Shadow Falloff
The distance from the light at whi= ch shadow falloff begins. -1.0 turns off shadow falloff. This is used along= with Shadow Max Distance to create a false fade for shadows that are reduce= d or cut off by the Shadow Max Distance parameter. Below is an example with = both parameters being used and the falloff is increased. Note this pa= rameter may impact performance on complex lighting setups.
Shadow Falloff Gamma
The gamma of the shadow strength i= n the falloff zone. This requires the use of Shadow Ma= x Distance and = Shadow Falloff .
Trace Subset
Set of geometry to consider for traced shadow intersection. If this is n= ot specified, all geometry are considered for traced shadow intersection.= p>
Don't Trace Subset
Set of geometry to ignore for traced shadow intersection. If this is not= specified, all geometry is used for traced shadow intersection.
Trace Light Paths
Enable light and photon tracing fr= om this light. This value enforces a physically-based light and as a side-e= ffect disables the above Shadows controls. Users may use this feature to se= lectively decide which lights emit photons when using the PxrVCM or PxrUPBP= Integrators.
Thin Shadow
Enable thin shadow and disable ref= raction caustics for this light. This parameter will ignored if Trace Light Paths = is enabled. This is a non-physical control that creates "fake" colore= d shadows for transmissive objects without needing to generate photons for = caustics. Below we go from On (default) to Off (opaque shadowing). Notice w= e lose the colored shadows and interior colored reflection choosing Off, bu= t we gain some render speed instead.
Visible in Refraction
Make a light visible through transmission effects like glass and windows= by turning this on.
Manifold Walk
Used with the PxrUnified Integrator and enabling Enable Man= ifold Walk to create inexpensive caustics. Note: You must dis= able Thin Shadows
Manifold Walk Exclude Group
Used with the PxrUnified Integrator and enabling Enable Man= ifold Walk, this trace set is ignored during manifold explora= tion to avoid stopping or shadowing manifold exploration rays
Light Samples
Specifies an override of the number of light samples to be taken for thi= s light source. If set to something other than zero, it will override the s= ampling performed by the integrator. You might find need for this if you ha= ve unsolvable noise from this light and need more samples.
Light Group
Specify the light group name used for light group LPEs. This is useful t= o generate per-light AOVs for later adjustment in compositing.
Importance Multiplier
Rather than setting explicit Light Samples, users can change the amount = of samples the light will be assigned internally by changing this value. Re= nderMan creates a set of samples at render time for all lights in the scene= and changing this value rebalances the samples across the lights. Note tha= t increasing this value will cause more sample= s to be selected from this light while reducing it for others in the scene.= Lower than the default will decrease the samples while = providing more to others in the scene.
RenderMan for Maya includes useful presets for specific times of day.