## Photometrics Calculations Taking Too Long

Posted on August 8th, 2023. Last updated on August 8th, 2023.

Q: My photometric calculations take forever to complete. What can I do to reduce the calculation time?

A: Several factors influence how long it takes to perform photometrics calculations, each of which is described below. If you want the photometrics to calculate faster, reduce one or more of these factors. They are listed in order of their impact on the calculation time.

### 1. Number of Calculation Points

#### Context

The most common problem is the software is simply trying to calculate too many illuminance level points on the drawing. The more calculation points you have in your area, the longer the calculation will take.

The number of points for which the illuminance level is calculated in a calculation area can be roughly calculated using the formula A / GS², where A is the total area being calculated and GS is the Grid Spacing setting for the area. For example, a calculation area for a 50,000sf site at 10′ grid spacing will have approximately 500 calculation points (50,000 / 10²).

#### Solution

First, make sure your Distance Unit setting in the Calculate General Photometrics or Calculate Egress Photometrics command matches the base unit of your drawing. If they do not match, the software could try to calculate up to 144 times as many points as you actually want. As such, your calculations will take significantly longer, and the results will not be accurate. See the Base Units and Photometrics Calculations article for more information.

To reduce the number of calculation points, increase the grid spacing of the area, or split the area into multiple smaller areas and only calculate the area in which you are actively working.

Using the example above, if you divide the 50,000sf site into two 25,000sf calculation areas, the number of calculation points in each area drops to 250. If you increase the grid spacing from 10′ to 20′, the total number of calculation points drops to 125.

### 2. Reflections

#### Context

If the Reflections setting in the Calculate General Photometrics or Calculate Egress Photometrics command is set to Single, calculation areas defined with walls or ceilings, as well as lines drawn using one of the Insert Photometric Solid commands, such as Insert Photometric Solid: Shape, must be accounted for to determine whether and how much light is reflected to the ground from light fixtures. If this setting is enabled, the calculation time related to light-obstructing lines on the drawing is effectively doubled.

#### Solution

For most site lighting projects, such as large parks or parking lots, disabling reflections is recommended unless you are confident the reflections from light-obstructing objects on your drawing will significantly impact the calculation results.

For indoor lighting, disabling reflections is not recommended, as the reflections from walls and other light-obstructing objects can significantly impact the calculation results.

### 3. Number of Solid Faces

#### Context

Each line drawn using one of the Insert Photometric Solid commands, such as Insert Photometric Solid: Shape, must be accounted for to determine how it obstructs the light from fixtures. The more light-obstructing lines you have on the drawing, the longer the calculation will take.

#### Solution

When possible, you can reduce the number of light-obstructing lines to decrease the calculation time without significantly affecting the results. Here are two examples:

• Most round objects, such as trees and bushes, can be approximated using 4-8 lines.
• Rather than using 5 lines to draw a shallow alcove in the wall of a building, use a single straight line.

### 4. Number of Light Fixtures

#### Context

Each light fixture on the drawing must be accounted for when calculating the photometrics. This includes light fixtures outside the calculation boundary, as their light may spill over onto the area being calculated. The more light fixtures you have on the drawing, the longer the calculation will take.

#### Solution

While the number of light fixtures does impact the calculation time, we do not recommend adjusting your lighting design to reduce calculation times.

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