Creating an Irradiance Sensor

This page shows how to create an Irradiance Sensor that computes and analyzes irradiance and illuminance distribution. The irradiance sensor can be created with different integration types allowing you to integrate specific light directions in the sensor.

To create an Irradiance Sensor:

  1. From the Light Simulation tab, click Irradiance .
    The sensor appears in the 3D view and is placed on the origin of the assembly.
  2. In the 3D view, set the Axis System of the sensor by clicking to select one point for the origin, to select a line for the X axis, to select a line for the Y axis or click and select a coordinate system to autofill the Axis System.
    Note: If you define manually one axis only, the other axis is automatically (and randomly) calculated by Speos in the 3D view. However, the other axis in the Definition panel may not correspond to the axis in the 3D view. Please refer to the axis in the 3D view.

    Three bold arrows indicate the axis system of the sensor. The blue arrow corresponds to the Z axis and indicates the integration direction of the sensor.

    Important: Make sure the sensor is not tangent to a geometry.
    Important: Make sure the sensor does not intersect a volume body. The sensor must be located either completely inside the volume body or outside the volume body.
    Tip: To adjust the sensor position and orientation dynamically from the 3D view, you can also use the Move option (Design tab).
  3. From the Integration type drop-down list, select how the light should be integrated to the sensor.
    • Select Planar for an integration that is made orthogonally with the sensor plan.

    • Select Radial, Hemispherical, Cylindrical, Semi-cylindrical if you need to follow specific street lighting illumination regulations.

      Note: The Planar integration type suits most of the configurations.

      Other integration types available are dedicated to specific lighting regulations as they allow to study light in a specific plan (it can be useful to analyze the light contribution on road signs, pedestrian walkways or the road itself).

  4. If you selected Planar or Semi-cylindrical integration types, define an integration direction:
    1. In the 3D view, click .
    • For Planar, select a direction in the 3D view.
    • For Semi-cylindrical, select a line that is parallel to the sensor plan.
    1. If you need to adjust the integration direction axis, use Reverse direction.
  5. If you want to use a XMP Template to define the sensor, in XMP Template, click Browse to load a *.xml file.

    A XMP Template is a *.xml file generated from a XMP result. It contains data and information related to the options of the XMP result (dimensions, type, wavelength and display properties).

    When using a XMP Template, measures are then automatically created in the new *.xmp generated during the simulation based on the data contained in the template file.

    • If you want to inherit the axis system of the sensor from the XMP Template file, set Dimensions from file to True.

      The dimensions are inherited from the file and cannot be edited from the definition panel.

    • If you want to define the radiance sensor according to display settings (grid, scale etc.) of the XMP Template, set Display properties from file to True.
  6. In General, from the Type drop-down list:

    • Select Photometric if you want the sensor to consider the visible spectrum and get the results in lm/m2 or lx.

      Note: In case of a photometric result generation, the International Commission on Illumination (CIE) defines the visible spectrum as follows: "There are no precise limits for the spectral range of visible radiation since they depend upon the amount of radiant flux reaching the retina and the responsivity of the observer. The lower limit is generally taken between 360 nm and 400 nm and the upper limit between 760 nm and 830 nm".

    • Select Radiometric if you want the sensor to consider the entire spectrum and get the results in W/m2.

      Note: With both Photometric and Radiometric types, the illuminance levels are displayed with a false color and you cannot make any spectral or color analysis on the results.
    • Select Colorimetric to get the color results without any spectral data or layer separation (in lx or W/m2).

    • Select Spectral to get the color results and spectral data separated by wavelength (in lx or W/m2).

      Note: Spectral results take more time to compute as they contain more information.
  7. If you want to generate a ray file containing the rays that will be integrated to the sensor, from the Ray file drop-down list, select the ray file type:
    • Select SPEOS without polarization to generate a ray file without polarization data.
    • Select SPEOS with polarization to generate a ray file with the polarization data for each ray.
    • Select IES TM-25 with polarization to generate a .tm25ray file with polarization data for each ray.

    • Select IES TM-25 without polarization to generate a .tm25ray file without polarization data.

      Note: The size of a ray file is approximately 30MB per million of rays. Consider freeing space on your computer prior to launching the simulation.
      CAUTION: If the surface that will be used for the creation of the ray file is fully absorbent (SOP set to Mirror 0%), all rays are absorbed and no ray will be integrated in the ray file. This ray file will be empty.
  8. From the Layer drop-down list:
    • Select None to get the simulation's results in one layer.

    • Select Source if you have created more than one source and want to include one layer per active source in the result.

      Note: You can change the source's power or spectrum with the Virtual Lighting Controller in the Virtual Photometric Lab or in the Virtual Human Vision Lab.

    • Select Face to include one layer per surface selected in the result.

      Tip: Separating the result by face is useful when working on a reflector analysis.

      • In the 3D view click and select the contributing faces you want to include for layer separation.

        Tip: Select a group (Named Selection) to separate the result with one layer for all the faces contained in the group.
      • Select the filtering mode to use to store the results (*.xmp):

      • Last Impact: with this mode, the ray is integrated in the layer of the last hit surface before hitting the sensor.
      • Intersected one time: with this mode, the ray is integrated in the layer of the last hit selected surface if the surface has been selected as a contributing face or the ray intersects it at least one time.

    • Select Sequence to include one layer per sequence in the result.

      • Define the Maximum number of sequences to calculate.
      • Define the sequences per Geometries or Faces.
      • Sort the sequences per Relative energy or Peak value.
      Note: Separating the result by sequence is useful if you want to make a Stray Light Analysis. For more information, refer to Stray Light Analysis.

    • Select Polarization to include one layer per Stokes parameter using the polarization parameter.

      Stokes parameters are displayed using the layers of the Virtual Photometric Lab.

    • Select Incident angles to include one layer per range of incident angles, and define the Sampling.

      For more information on the data separated by Incident angles, refer to Understanding the Incident Angles Layer Type.

  9. Define the dimensions of the sensor:
    • If you want to symmetrize the sensor by linking Start and End values, set Mirrored extent to True.

    • Edit the Start and End positions of the sensor on X and Y axes.

      Tip: You can either use the manipulators of the 3D view to adjust the sensor or directly edit the values from the definition panel.

    • Adjust the Sampling of the sensor or the Resolution. The sampling corresponds to the number of pixels of the XMP map and the resolution to the size of one pixel sample.

      Note: Speos supports a maximum resolution of 23170 * 23170 pixels.
  10. If you selected Spectral or Colorimetric as sensor type, set the spectral range to use for simulation.
    • Edit the Start (minimum wavelength) and End (maximum wavelength) values to determine the wavelength range to be considered by the sensor.
    • If needed, in Sampling, adjust the number of wavelengths to be computed during simulation, or in Resolution adjust the interval between two wavelength samples.
  11. If you intend to use the sensor for an inverse simulation, define the Output faces that the rays generated from the sensor will aim at during the simulation to improve performance:
    1. In the 3D view, click .
    2. Select the Output faces you want the sensor to focus on for the inverse simulation.
    Important:
    In simulation:
    • In CPU, for each pixel per pass, if the ray emitted by the CPU does not intersect an output face, the CPU will emit again a ray until the ray intersects an output face.
    • In GPU, for each pixel per pass, the GPU emits one ray whatever it intersects or not an output face. GPU does not emit again if the ray does not intersect an output face.

    That means, for a same number of pass, CPU does converge better than GPU. To get the same result on GPU, you need to increase the number of pass.

  12. If you want to display sensor grid in the 3D view, in Optional or advanced settings set Show grid to True.
The Irradiance Sensor is created and appears both in Speos tree and in the 3D view.