Sources - Power Tab

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Power Tab

Page Contents

Description

•Power units

Description

The Power Tab of a Detailed Source dialog has three functions:

•Set the total Power of the source after the Position Apodization and Direction Apodization have been applied to the rays.

•Set the Position Apodization for the ray positions defined.

•Set the Direction Apodization for the ray directions defined.

Navigation

This feature can be accessed by selecting the Power tab in a Detailed Source dialog box.

Controls

Control	Inputs / Description	Defaults
Total Power	The total power of the source. Rays in the source are scaled after both the position and direction apodization functions have been applied.	1
Power Units	Units of the value entered for Total Power. Available options are: •Unspecified •Watts •Lumens NOTE: Lumens cannot be used unless a spectrum has been specified on the Wavelengths tab of the source dialog.	Unspecified
Position Apodization
Type	Pull down menu of available position apodization options: •Uniform •Gaussian •Rn distance from a given point •Amplitude/Phase Mask •Super-Gaussian	Uniform
Direction Apodization
Type	Pull down menu of available direction apodization options: •Uniform •Lambertian •Inverse Lambertian •Gaussian •Cosn or Sinn •Sampled (spherical angles) •Super-Gaussian	Uniform

OK	Accept settings and close the dialog box.
Cancel	Discard settings and close the dialog box.
Apply	Apply settings and keep the dialog box open.
Help	Access this Help page.

Application Notes

Power units

Three power units are available, Unspecified, Watts and Lumens.

By default FRED sets source units to Unspecified, which are arbitrary radiometric units. With these units, the results of analyses such as irradiance and intensity will be of the form Power/Area and Flux/Steradian as reported in the output window and analysis plots. If the source power units are unspecified and an Illuminance or Luminous Intensity calculation is performed, the units of the calculations will be in Arbitrary Units.

If Watts are selected, calculations proceed exactly the same as Unspecified units, though the output window and plots will correctly display the proper unit designation. Additionally, if a source has units of Watts, then Illuminance and Luminous Intensity calculations will show proper photometric units such as Lux, Phot, Candela etc.

When units of Lumens are specified, a spectrum and wavelength range must be selected from the Wavelengths tab of the detailed source dialog. In this case, the source wavelengths are chosen Monte-Carlo according to the spectral power distribution of the spectrum. A sampled wavelength list cannot be used to accurately convert between photometric and radiometric units for the following reasons:

1.		The weighting in a wavelength list specification defines the relative area underneath the spectrum at the sample point and does not specify the actual spectral value of that wavelength
2.		The wavelength list specification does not explicitly define the bandwidth limits of the spectrum

Realized Lumens

When a source is created, the following information is printed to the output window:

Ray Count - Number of rays created at the source.

Specified Power - Value entered in the Power tab of the source definition.

Arrayed Power - Total power for an arrayed source. This power is not necessarily a scaled version of the base source, since each arrayed source may have randomized characteristics.

Power Units - Specified power units on the Power tab of the source definition.

Realized Lumens - Reported only when the source units are Lumens and reflects the actual power of the source using the generated rays and calculated luminous efficacy.

Name - Name of the source.

For sources whose power units are specified as Lumens, it is advisable to review the Realized Lumens output after creating the source for comparison against the specified power. The realized Lumens value is the actual calculated photometric power of the source using the rays generated during source creation and can be an indicator of the how accurately the source's spectrum is represented by the generated rays.