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Illuminance Values Not as Expected

The illuminance values in my photometrics project aren't what I expected. What should I check?​

Several factors, described below, can affect the results of photometrics calculations. Verify that each of these factors is correct.

IES File & Photometric Information​

Confirm that the information in the Photometric Calculation Information and IES File sections of the Light Fixture Project Schedule for each light fixture is consistent with the manufacturer specifications for that fixture. For example:

  • Illuminance values for non-LED fixtures will be affected by the Number of Lamps and Lumens/Lamp values, in addition to the information from the IES file.
  • If the fixture uses multiple LEDs or sets of LEDs, but the IES file is only for one LED or set of LEDs, the Scale Factor must be modified to increase the IES file output.

Inserted Light Fixtures​

For light fixtures inserted on the drawing, use the Query command to confirm they are using the correct Callout ☰ and the appropriate Arm Length, Mounting Height, and Tilt settings. Visit the Light Fixture Tilt, Arm Length, & Elevation article in the knowledge base for more information about how those fields affect light fixture output.

Calculation Settings​

Confirm that the Distance Unit ▾ field in the Calculate Photometrics dialog box, as well as the AutoCAD variable DIMSCALE, are appropriate for the scale of your drawing. Visit the Base Units & Photometrics Calculations and Light Fixtures & Text Not Scaling Correctly articles in the knowledge base for more information.

If comparing the calculated illuminance values to documentation provided by the manufacturer, use the Query command on the calculation area, then press the button to center the displayed values directly underneath the light fixture being compared.

When Calculated Results Are Still Unexpected​

Design Master Photometrics performs calculations strictly based upon the IES files and user-specified information provided. If you have verified the user-specified inputs, the calculated illuminance values should be considered correct. In that case, an evaluation of the lighting design—such as light fixture selection and placement—may be needed to proceed.