A uniform light emits light with a constant radiance and the same spectrum across the surface :

• The light is uniform : its intensity is defined by a custom spectrum,

• The angular behaviour of the light is a model,

• The spectral behaviour of the light is a model.

A uniform light placed on a plane will have a lambertian behaviour, a uniform light placed on a sphere will act like a physical point light.

To create a uniform light in your scene, you must first create a spectral and polarized area light. Then, you must change the light intensity type to “Uniform”.

A uniform light has the following properties :

• Emit on both sides : whether the light emits light on both sides of the geometry or only in the direction of the normals. See the area light geometries section for more details.

• Spectrum : the spectrum emitted by the light source. The spectrum will be scaled to fit the intensity given by the angular measure of the light source. See the spectrum section for more details on spectrums.

Currently, Predictive Engine only supports one type of measured display.

The measurement of a display is performed using ELDIM EZConstrast MS88 and consists in measuring the emitted angular spectral radiance for each red, blue and green channels at nine pixel levels : 0, 31, 63, 95, 127, 159, 191, 223, 255. Each measurement should be exported from the ELDIM proprietary format (.i3dx) to the ELDIM binary data format (.dat).

A display (or HUD screen) is an emitting rectangular surface made of pixels. Each pixel can emit a different colour but they all have the same angular and spectral behaviour :

• The light is not uniform : its intensity is defined by a custom texture (intensity of the R,G,B channels of each pixel),

• The angular behaviour of the light is measured,

• The spectral behaviour of the light is measured.

To create a measured display in your scene, you must first create a spectral and polarized area light. Then, you must change the light intensity type to “Measured Display”.

A measured display has the following properties :

• Texture : the RGB texture that will be displayed on the pixel grid. The position of the texture on the surface is defined by the geometry’s UVs.

• Measure : the angular and spectral measure of one pixel of the screen in W/m²/sr/nm.

The measure should be composed of three directories (“blue”, “green”, and “red”) each containing the set of measurements for the corresponding pixel channel. You can give the three directories separately, or give one main directory that contains the three directories.

One set of measurement is composed of nine *.dat files, one for each pixel level of the given channel. Files are read in lexicographic order so we recommend to add trailing zeros in the file name, for instance : red031.dat for pixel level 31 of the red channel.

A radiometric light emits the same spectrum across its surface, the emitted spectrum is stored with the angular and spectral behaviour measure :

• The light is uniform : its intensity is defined by a measured spectrum,

• The angular behaviour of the light is measured,

• The spectral behaviour of the light is measured.

To create a radiometric light in your scene, you must first create a spectral and polarized area light. Then, you must change the light intensity type to “Radiometric”.

A radiometric light has the following properties :

• Spectral Image : the texture that contains the angular and spectral measure of the light source in W/sr/nm. See the Spectrums section for more details on spectral images.
  The image is parametrized according to an equi-rectangular (or panoramic) projection of the sphere with the top and bottom rows corresponding to an inclination of 0 and 180 degrees respectively. The left column corresponds to an azimuth of 0 degrees.

A photometric light is similar to a radiometric light but its emitted spectrum is not stored with the angular and spectral behaviour measure :

• The light is uniform : its intensity is defined by a custom spectrum,

• The angular behaviour of the light is measured,

• The spectral behaviour of the light is measured.

To create a photometric light in your scene, you must first create a spectral and polarized area light. Then, you must change the light intensity type to “Photometric”.

A photometric light has the following properties :

• Spectrum : the spectrum emitted by the light source. The spectrum will be scaled to fit the intensity given by the angular measure of the light source. See the spectrum section for more details on spectrums.

• IES File : the *.ies file that contains the angular measure of the light source in candela (cd).