Calculated Success

Lighttools® Soft Egg Crate® EggCalc Calculator

Predicting the illuminance - the amount of light - at some distance from a large diffuser can be difficult. The inverse square law only applies to point sources of light, which hardly describes a diffuser when viewed at close range!

The problem becomes more acute when you place a Lighttools® Soft Egg Crate® in front of the diffuser to control the light distribution.

EggCalc performs these calculations for you. It determines the distribution of light from large diffusers at any distance on or off center axis both with and without Standard Soft Egg Crates®.

For assistance, please call Lighttools Canada @1.800.417.7431 (N. America toll free) or 1.780.438.3860

Lighttools® and Soft Egg Crates® are trademarks of Lighttools® Inc.

EggCalc was developed for Lighttools® by:
Ian Ashdown, P. Eng., LC
byHeartConsultants Limited
www.helios32.com

Using EggCalc is simple:

1. If you are using a diffuser with a Lighttools® Soft Egg Crate®, choose the appropriate model from the drop-down Model list. Otherwise, choose None.
2. Select the appropriate beam spread from the drop-down Style list.
3. Select the Width and Height of your diffuser from the drop-down lists.
4. Specify your meter position.

The Distance is measured along a line extended from and perpendicular to the center of the diffuser. The Horizontal and Vertical distances are offsets from this line. The meter is always facing in the direction perpendicular to the diffuser. (Imagine placing the meter on a surface that is parallel to the diffuser.)

The Relative Illuminance values are shown in f-stops for both the bare diffuser and the diffuser with an egg crate screen. These values are relative to a light meter reading taken a few inches away from the center of the bare diffuser.

EggCalc assumes that you are using a perfect diffuser. If you can easily see the light source through the diffusion material, then the light is being only partially diffused, and EggCalc will produce only approximate results. Even so, these results will be much better than trying to guess with the inverse square law.