A simple light meter with three filter covered photocells (current source symbols). Photo store Written gelatin filters in 2 inch square sheets are Eastman Kodak red # 25A, green #58, and blue #47 cut to photocell size using scotch or masking tape covering as little of light surface as possible.
Three sub miniature 50000 ohm potentiometers, three position rotary switch shown as single switches above 0-50 D.C. microamp meter.
Set meter: White light source (sunlight, for example) on white paper sheet to full scale readings on separate colors.
For dependable service: good white light source, keep same distance between photocells and test samples, and test samples of same texture.
