Analyses - Illuminance

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Illuminance

Page Contents

Description

Navigation

Controls

Application Notes

•Source unit implications

•Detector response spectrum

•Image artifact diagnostic tool

Related Topics

Description

An Illuminance analysis gives results in Luminous Flux / Area. When all source units are specified (i.e. Watts or Lumens), the Illuminance calculation allows output in LUX (lm/m²), Phot (lm/cm²), Foot Candles (lm/ft²), Lumens/SysLengthUnit² (lm/area), or Arbitrary (specify response spectrum). If not all source units are known, then the Illuminance calculation only allows output as Arbitrary (not all source power units are known). The Illuminance analysis should be used in place of the Irradiance analysis when Photometric considerations are required or when a user defined detector response is needed. This analysis can be applied to both incoherent and coherent sources, though it is not possible to set the ray wavelength generation method to "Random according to spectrum" when using a coherent source.

Navigation

This command can be accessed in the following ways:

•Menu > Analyses > Illuminance

•Toolbar button:

Controls

Control	Inputs / Description	Defaults
Use This Analysis Surface
Use This Analysis Surface	Lists the analysis surface used to filter the rays.	Selected analysis surface
List of Available Analysis Surfaces
List of Available Analysis Surfaces:	Lists the available analysis planes for use as the ray filter.	Valid analysis surfaces
Pre-Analysis Ray Operations
Delete old rays and recreate all active sources	If checked, existing rays are deleted, and new rays are created before the analysis proceeds.	Unchecked if rays exist. Checked if no rays exist.
Raytrace all active rays	If checked, any existing rays are raytraced before the analysis is performed.	Unchecked if rays exist. Checked if no rays exist.
Plot the rays as they are being raytraced	If checked the rays will be drawn to the 3D view when traced.	Unchecked
Output Units
Output Units	Options depend on the source power definitions. When ALL traceable sources have power units of Watts or Lumens: •LUX (lm/m²) •Phot (lm/cm²) •Foot Candles (lm/ft²) •Lumens/SysLengthUnit² (lm/area) •Arbitrary (specify response spectrum) When ANY traceable source has power units of Unspecified •Arbitrary (not all source power units are known)	LUX (lm/m²) when all source units are known Arbitrary when not all source units are known
Detector Response
Spectrum	Spectrum to be used as the detector response function	None
Scale factor	Scale factor applied to the detector response	1
Post-Analysis Operations
Create Analysis Results Node (ARN)	Adds an Analysis Results Node (ARN) to the Analysis Results folder on the object tree. The ARN being created stores the results of, and information about, the analysis being performed.	Unchecked
Name Prefix	The name of the ARN on the tree will be formed by combining this name prefix with an automatically generated numeric value, ensuring that the resulting ARN has a unique name string.	Illuminance

OK	Perform analysis and close dialog box.
Cancel	Discard analysis and close dialog box.
Help	Access this Help page.

Application Notes

Source unit implications

In its basic operation (no detector response), the Illuminance calculation will only report the photometric units of Lux, Phot, Foot Candles or Arbitrary/SysLengthUnit² when the source units are known (i.e. Watts or Lumens). If the source units are not known the Illuminance calculation will still proceed by integrating the source spectral distribution with the photopic response curve and multiplying by the scale factor, but the units are not guaranteed to be Lux, Phot or Foot Candles. Therefore, when the source has Unspecified units the only available option in the Illuminance calculation will be "Arbitrary (not all source power units are known)". These units can be interpreted as arbitrary photometric units.

Detector response

When the source units are specified (i.e. Watts or Lumens), the Illuminance calculation allows a user specified detector response function to be used rather than the standard photopic response curve and luminous efficacy value. In terms of the conversion to photometric units, the detector response function has the following application:

In this case we are not necessarily integrating with the photopic response curve or setting the appropriate scaling factor and so the resulting units are not necessarily photometric units. The end units are therefore arbitrary but not guaranteed to be arbitrary photometric.

It is therefore possible to recover photometric units in an Illuminance calculation by two methods:

1) Perform an Illuminance calculation using any of the photometric unit options.

2) Perform an Illuminance calculation using the a photopic response curve as the Detector Response and a scale factor of 683.

Image Artifact Diagnostic Tool

If a raytrace has been performed using the Advanced Raytrace option with ray paths enabled, contributing raypath information for a particular region of interest can be reported directly from the chart view for an incoherent spatial analysis or analyses using a Directional Analysis Entity. This feature can be executed by holding down the ALT keyboard button while using the mouse to select a region of the main chart view (turn of "perspective view" using the right mouse button menu option). This procedure is outlined in the following example:

1.Perform an Advanced Raytrace (ray paths on).

2.Perform an incoherent spatial or directional analysis (irradiance, illuminance, color image, position spots diagram).

3.In the main chart view hold ALT while using the mouse to select a region of interest (shown in red).

4.Resulting path information is printed to the output window.

The image artifact diagnostic tool will print the following information to the output window:

•Analysis surface used

•Selected region x-min, x-max, y-min and y-max

•Path number, path power and ray count for each contributing ray path (up to the first 30 paths, sorted by power)

•Remaining path count and total power for paths not listed in the output window