Light Passing through a Series of Color Filters

As Bill Beaty showed by inventing his Infrared Goggles, combining color filters allows you to create new applications. As an aid to create your own uses with color filters, use the FilterCombo software to estimate the intensities of light passing through a sandwich of color filters. It is quite difficult to calculate the effects of the light interacting with the surfaces of the gels, so use this as an estimate.

Use the data available for most color filters used in theater lighting. Example at right: the Rosco 049 (Medium Purple) filter, which is used to make the plant stress detection devices.

The transmission is the intensity of light passing through the filter. 100% transmission means all of the color or wavelength passes through the filter. 50% transmission indicates that only 50% of the light shining on the filter passes through the filter and 50% is absorbed by the filter. If none of a color passes through the filter, then the transmission is 0%.

Getting Started

NOTE: The images that follow are not interactive. Please download the software (OSX OS9 PC) and follow along with the mini tutorial.

Filters may be created with the software or with spreadsheet or word processing software. Review a sample of text file for the Rosco 049 filter.

To create the transmission of a filter with software, click on 'Make Filter File' and file in the following information:

The 'Save Plot' button saves the data to a text file and then plots the results. This allows you to create the file once and use it efficiently the next time. 'Plot Only' does not save the file.

To graph the amount of light passing through two Rosco 049 filters, click 'Open File Filter' (if you saved the text file above) in Filter 2. Since Filter 1 (in blue) and Filter 2 (plotted in red) are identical, only the red line shows. The transmission spectrum of light passing through the two filters is drawn in black.