This one-sided area light simulates a rectangular shaped light source.
Its usage includes illuminating objects, simulating soft boxes used in photography, linear lights, fluorescent lights, and light panels. This is also used for adding bounce lighting off the walls.
You will see mention of "non-physical" controls. These controls are designed to help artists make art-directed imagery by ignoring certain laws of physics we usually simulate.
Scales the contribution of this light linearly. The light intensity is computed using physical falloff. Below the Intensity parameter increases by 1.0 each render.
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. Real world lighting has high energies and typical exposures are low values while you may have to type a really large number for equivalent Intensity . This is also comfortable to artists familiar with photographic measurements. The intensity is reset to 1.0 so the result starts darker than above because of the physical falloff of the light.
An image to use as a light source. Preferably a High Dynamic Range source. Below there are three different images used. Notice this affects color and shadowing based on the contents of the HDRI used. If forced to use an 8-bit source such as a JPEG image, it should be linearized (transformed to linear color space) before use as a color.
The color of the emitted light. If a color map is specified, this tints the light.
Gamma-correct the texture. Each channel (RGB) can be adjusted independently.
Turns color temperature on or off.
The effect will be less pronounced on fully saturated mono-chromatic lights. Defaults to 6500K, which should be very close to white on most monitors (D65 illuminant used by sRGB and Rec 709).
Off-axis cosine power exponent to shape the emission. This controls the spread of the light. Higher numbers will start focusing the light towards the center and thus narrowing the light spread.
Emission Focus Tint
Off-axis light color tint. This tints the emission in the falloff region starting from the off-angle direction of the light towards the center. By default, the tint color is black (none). In addition to tinting, values greater than white will also increase the intensity of the falloff region. Notice when using White the emission focus nearly appears to be off.
Amount of specular light that is emitted. This is a non-physical control. You could use a light with Specular Amount 0.0 to act purely as a source of diffuse light for your scene objects and avoid adding highlights. This scene has subtle reflections but you can notice the light disappears from the reflection in the chrome ball far right.
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.
Intensity Near Dist
Near distance at which the point being illuminated and the light at which the sample doesn't get brighter. This may help you avoid hot spots and sampling issues where a light is near a surface. These values are based on your scene scale/distance so this is just an example.
Angle of the virtual flaps on the light to turn it into a spotlight. This does not affect IES Profiles (should you be using one).
Softness of the cut-off of the Cone Angle. The regular range is from 0 (hard cut-off) to 1 (smooth transition), but it can be set higher than 1 for additional gradation. Above in the Cone Angle you notice how hard the edges look, this parameter improves that result to be more pleasing.
Name of an IES light profile. Below makes use of three different IES profiles and some dark mood lighting.
Rescales the angular distribution of the IES profiles. Values less than 0 specify that the profile represents less angular coverage, and will effectively increase the size of the projected profile. Defaults to 0 for full coverage (no scaling).
All shadow parameters will be ignored if the light's Trace Light Paths is enabled in Advanced. The below options are all non-physical controls when used out of their default state. If Trace Light Paths is enabled then their physical nature is enforced.
Enable raytraced shadows.
The color of the shadows cast by emitted light.
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 light. You may use this control to artificially reduce the distance shadows are cast. This may also increase render speed by not calculating shadows outside this distance. Here it's used to remove the shadow off the back wall from the flashbulb effect of the light.
The distance from the light at which 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 reduced 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 parameter may impact performance on complex lighting setups.
Shadow Falloff Gamma
The gamma of the shadow strength in the falloff zone. This requires the use of Shadow Max Distance and Shadow Falloff .
Set of geometry to consider for traced shadow intersection. If this is not specified, all geometry are considered for traced shadow intersection.
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.
When normalize is enabled, the amount of light contributed to the scene will not change as you scale the light source. This makes it easier to adjust highlight size without changing scene lighting.
Trace Light Paths
Enable light and photon tracing from this light. This value enforces a physically-based light and as a side-effect disables the above Shadows controls. Users may use this feature to selectively decide which lights emit photons when using the PxrVCM or PxrUPBP Integrators.
Enable thin shadow and disable refraction caustics for this light. This parameter will ignored if Trace Light Paths is enabled. This is a non-physical control that creates "fake" colored shadows for transmissive objects without needing to generate photons for caustics. Notice we lose the colored shadows and interior colored reflection choosing Off, but we gain some render speed instead.
Specifies an override of the number of light samples to be taken for this light source. If set to something other than zero, it will override the sampling performed by the integrator and can result in a performance impact. It's recommended to leave this at the default unless you experience unsolvable noise from the light.
Specify the light group name used for light group LPEs. This is useful to generate per-light AOVs for later adjustment in compositing.
Rather than setting explicit Light Samples, users can change the amount of samples the light will be assigned internally by changing this value. RenderMan 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 that increasing this value will cause more samples 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.