Lights intensity
Lights intensity
Embedded Files
A light source does not necessarily emit light uniformly, the emitted light will be more or less intense :
depending on the position on the light's surface (uniformity),
depending on the angle at which you look at the light (angular behaviour), and
depending on the wavelength of the light (spectral behaviour).
These variations in the intensity can be measured and can be simulated in Predict Engine.
The definition of a light's intensity on the UVR Light Settings component depends on the light type :
Directional lights
Directional lights
Lights of type "Directional" are perfect models that simulates the light coming from a single direction like an infinitely small point, infinitely far away.
Since the light is infinitely small, it is considered uniform. However, you can define an angular radius for the directional lights in the scene : the radius defines the angular size of the point it comes from in the sky, just like a sun,
Because the light comes from a single point infinitely far away, it comes in a single direction and it has no angular behaviour settings,
The spectrum of the light can be defined by the user in different ways, see the Spectrums section for more details on spectrums. Its irradiance can be modulated by :
A scaling coefficient,
An illuminance or irradiance value : in this case, the coefficient applied to the spectrum is automatically computed so that the illuminance of the light reaches the required value,
A preset value.
A directional light irradiance section has the following properties :
Quantity type : how the irradiance is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected irradiance or illuminance value,
Spectrum : the spectrum emitted by the light source. See the spectrum section for more details on spectrums.
You can find other orders of magnitude for the expected illuminance values here : https://en.wikipedia.org/wiki/Orders_of_magnitude_%28illuminance%29.
There can only be one sun in the sky at a time in Predict Engine. The lights that are considered to be suns are : directional lights with a non-null radius, and environment lights. If an environment light is defined on the camera currently rendering, all directional lights in the scene will be considered as perfect : their radius will be ignored.
Luminaire lights (Point lights, Spot lights, Area lights)
Luminaire lights (Point lights, Spot lights, Area lights)
Luminaire lights are defined by their intensity profile. They can be of any form.
Uniform lights
Uniform lights
A uniform light emits light with a constant intensity and the same spectrum across the surface :
The light is uniform : its intensity is the same at every position on the surface,
The angular behaviour of the light is a model : the intensity is constant,
The spectrum of the light can be defined by the user in different ways, see the Spectrums section for more details on spectrums. Its intensity can be modulated by :
A scaling coefficient,
A power value : in this case, the coefficient applied to the spectrum is automatically computed so that the power of the light reaches the required value,
A preset value.
A uniform light intensity has the following properties :
Quantity type : how the power is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected power value,
Spectrum : the spectrum emitted by the light source. See the spectrum section for more details on spectrums.
You can find other orders of magnitude for the expected power values here : https://en.wikipedia.org/wiki/Lumen_%28unit%29.
The uniform light model is mainly designed to mimic the behaviour of spherical lights. To model planar light sources, please look into lambertian lights.
Lambertian lights
Lambertian lights
A lambertian light emits light with a constant luminance and the same spectrum across the surface :
The light is uniform : its intensity is the same at every position on the surface,
The angular behaviour of the light is a model : the luminance is constant, which mean the intensity is defined with a cosine rule,
The spectrum of the light can be defined by the user in different ways, see the Spectrums section for more details on spectrums. Its intensity can be modulated by :
A scaling coefficient,
A power value : in this case, the coefficient applied to the spectrum is automatically computed so that the power of the light reaches the required value,
A preset value.
A lambertian light intensity has the following properties :
Quantity type : how the power is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected power value,
Spectrum : the spectrum emitted by the light source. See the spectrum section for more details on spectrums.
You can find other orders of magnitude for the expected power values here : https://en.wikipedia.org/wiki/Lumen_%28unit%29.
The lambertian light model is mainly designed to mimic the behaviour of planar lights. To model spherical light sources, please look into uniform lights.
Radiometric lights
Radiometric lights
A radiometric light is entirely defined by a single measure :
The light is uniform : its intensity is the same at every position on the surface,
The angular behaviour of the light is measured,
The spectrum of the light is measured. Its intensity can be modulated by :
A scaling coefficient,
A power value : in this case, the coefficient applied to the spectrum is automatically computed so that the power of the light reaches the required value,
A preset value.
A radiometric light has the following properties :
Input Quantity : defines whether the values inside the texture describe the intensity or the luminance of the source,
Quantity type : how the power is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected power value,
Definition : defines whether the measure is RGB or spectral,
Texture : the texture that contains the angular and spectral measurement of the light source in W/sr/nm. If the measure is spectral, 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,
Gamma : if the measure is RGB, the gamma correction that is applied to the texture values.
You can find other orders of magnitude for the expected power values here : https://en.wikipedia.org/wiki/Lumen_%28unit%29.
Photometric lights : IES profiles
Photometric lights : IES profiles
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 the same at every position on the surface,
The angular behaviour of the light is measured,
The spectrum of the light can be defined by the user in different ways, see the Spectrums section for more details on spectrums. Its intensity can be modulated by :
A scaling coefficient,
A power value : in this case, the coefficient applied to the spectrum is automatically computed so that the power of the light reaches the required value,
A preset value.
A photometric light has the following properties :
Quantity type : how the power is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected power value,
Spectrum : the spectrum emitted by the light source. See the spectrum section for more details on spectrums.
IES File : the *.ies file that contains the angular measurement of the light source in candela (cd). A preview of the IES file content is displayed bellow this field, it gives you information on the content of the measure :
The measure is displayed in the lower emission hemisphere. If the measure contains values in the upper hemisphere as well, it will be displayed accordingly,
The curves represent the intensity of the light in two perpendicular planes (0° and 90°, the reference 0° being given inside the file content),
When the measure contains data in a very large range, you can display the curves using a log scale,
Additional data about the measure (type, luminance, geometry) is displayed on the left if the window is wide enough.
IES lights can be previewed in the Unity Scene view using Gizmos :
Gizmos are enabled by clicking on the "Gizmos" button in the top right corner,
The gizmo is visible if the IES light GameObject is active in the scene and the "UVRLightComponent" line is enabled in the Gizmos menu,
The gizmo size is controlled by the "Gizmo Size" field in the IES light intensity section, the "Log Scale" toggle also affects the gizmo.
You can find other orders of magnitude for the expected power values here : https://en.wikipedia.org/wiki/Lumen_%28unit%29.
The *.ies file also defines a geometry associated with the light. You can load this geometry with the “Load IES Geometry” button. The geometry will be added to the light’s GameObject. The geometry dimension will be defined depending on the current scene scale.
The supported types for IES files are type A and type C only, type B is not supported yet.
If you need support for other formats like LDT or CIB, please contact us or use a third party converter.
Display lights (Area lights only)
Display lights (Area lights only)
Display lights represent displays of any kind (Screen, HUD, ...) and are defined by their luminance profile. They are expected to be planar.
Uniform display
Uniform display
A uniform display is similar to a uniform light except it is defined by its luminance profile instead of its intensity profile. It emits light with a constant luminance and the same spectrum across the surface :
The light is uniform : its luminance is the same at every position on the surface,
The angular behaviour of the light is a model : the luminance is constant,
The spectrum of the light can be defined by the user in different ways, see the Spectrums section for more details on spectrums. Its radiance can be modulated by :
A scaling coefficient,
A luminance or radiance value : in this case, the coefficient applied to the spectrum is automatically computed so that the radiance of the light reaches the required value,
A preset value.
A uniform light intensity has the following properties :
Quantity type : how the radiance is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected luminance or radiance value,
Spectrum : the spectrum emitted by the light source. See the spectrum section for more details on spectrums.
You can find other orders of magnitude for the expected luminance values here : https://en.wikipedia.org/wiki/Orders_of_magnitude_%28luminance%29.
RGB displays
RGB displays
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 modulated by a custom texture (levels of the R,G,B channels of each pixel),
The angular behaviour of the light is a model : the luminance is constant,
The spectral behaviour of the light can be defined by the user :
Each red, green and blue channel emits light with a given spectrum that is defined by the user, see the Spectrums section for more details on spectrums,
The intensity of each channel defines its weight in the final result,
The radiance of each pixel can be modulated by :
A scaling coefficient,
A luminance or radiance value : in this case, the coefficient applied to the spectrum is automatically computed so that the radiance of the light reaches the required value,
A preset value.
An RGB display has the following properties :
Quantity type : how the radiance is modulated,
Coefficient : the scaling coefficient,
Preset : the selected preset,
Expected Value : the expected luminance or radiance value,
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.
Red/Green/Blue pixels emission : the spectrum of emission for each pixel channel. The light emitted by a pixel will be the combination of all three channels modulated by their intensity in the texture for this pixel.
You can find other orders of magnitude for the expected luminance values here : https://en.wikipedia.org/wiki/Orders_of_magnitude_%28luminance%29.
Measured displays
Measured displays
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. Apart from the texture displayed on the screen, measured displays are entirely measured :
The light is not uniform : its intensity is modulated 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.
A measured display has the following properties :
Coefficient : a coefficient applied to the final intensity of each pixel.
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. 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).
The final 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.
Measured displays are big sets of data, they can take some time to load. You can enable an option in the performance settings of Predict Engine to load measured displays faster but with some imprecisions.
If you have display data in a different format, please contact us.
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