Lambertian emitter


Lambertian emitter

Emitter Lambertian emitters are isotropic over the half-sphere. They are seen having the same luminance from any direction. However, the emitted radiance will depend on incidence due to the cosine projection factor from the radiative transfer equations.

It is defined by:

  • A base light emission spectrum, setting dependence of radiance to wavelength
  • A filter shader modulating the radiance across the geometry surface

Luminous values may be normalized using the metric and quantity parameters as follows:

  • Custom metric : the emission properties are normalized to match the quantity defined by value and quantity
  • Base spectrum : base child defines the light quantity, as a spectral flux per instance or a spectral emittance per unit area, depending on the quantity parameter. multipler is unitless

It should be noted that all normalization occurs before the posmod function is applied.


This emitter was previously made using a Generic Emitter associated to a Lambertian Distribution before Ocean 2017 R5

Understanding metric

The actual physical emission values are derived from metric and quantity parameters

Metric Quantity Value Unit
Base spectrum Spectral flux (per instance) base * multiplier W/m
Base spectrum Spectral emittance base * multiplier W/m3
Base spectrum Spectral radiance base * multiplier
Custom Luminous flux (per instance) value lumen
Custom Luminous emittance value lumen/m2
Custom Luminance value cd/m2
Custom Energy flux (per instance) value W
Custom Energy emittance value W/m2
Custom Energy radiance value

For instance, in Base Spectrum Spectral Emittance mode, the base spectrum child values are multiplied by multiplier, and this sets the source emittance, in watts per wavelength unit (meters) per unit area (m²).

In Custom Luminous Flux mode, the value sets the lumen value per instance.

Children Nodes

Spectrum base The base emission spectrum
Filter shader posmod The spectral position modulation function


name type description
metric list Sets the metric mode (Custom or Base spectrum)
quantity list Sets the quantity or unit of the metric
value/multiplier real Defines the value (Custom metric) or the multiplier (Base spectrum metric)

Ocean XML 5.6.2 example

<emitter type="lambertian" name="emitter" metric="custom" quantity="lumflux" value="50">
     <spectrum type="blackbody" name="base" temp="3000" gain="1e-006"/>
     <filtershader type="constant" name="posmod" value="1"/>