Using Your Classroom Projector to Demonstrate Properties of Light Dr. Michael Ottinger and Dr. Brian Bucklein Missouri Western State University St Joseph, MO American Association of Physics Teachers 2012 Winter Meeting – Ontario, California February 6, 2012

Outline How are RGB images created? How do DLP, LCD and LCoS Projectors work? What are Spectral Glasses? Simple Demonstration of the Separation and Mixing of Colors using and LCD Projector Demonstration of the Polarization of Light

Three Color Image System Object RGB Filters Red Image Blue Image Green Image Low Pass High Pass

Three Color Image System Red Image Blue Image Green Image Superimpose Images Red Lamp Blue Lamp Green Lamp

Methods for Reproducing RBG (Common Types of Projectors) Digital Light Processing (DLP) Liquid Crystal Display (LCD) Liquid Crystal on Silicon (LCoS)

Digital Light Processing (DLP)

Texas Instruments DLP Chip: 921,600 mirrors (1280x720 pixels)

Liquid Crystal Display (LCD)

LCD Projector Light Source Red Dichroic Mirror Blue Dichroic Mirror LCD Chip Dichroic Combiner cube

Dichroic Combiner Cube

Liquid Crystal over Silicon

An LCoS Projector

LCoS Projector UHP Mercury Lamp Note: Green is Polarized Perpendicular to Red and Blue

Using the Projector to Teach Colors Diffraction Grating Glasses Available through many companies for about $0.25 to $0.45 each 500 lines/mm, linear diffraction grating

Breaking down the Colors The following slides were made by using the “Shapes” drop down in PowerPoint to make two thin rectangular lines. The top line was set to white and, using the color setting the bottom line was set to different color combinations.

White

Red

Green

Blue

Yellow = Red + Green

Magenta = Red + Blue

Cyan = Green + Blue

White = Red + Blue + Green

Polarization

LCD and LCoS Projectors use Polarized Light – Typically the Red and Blue have the same polarization – Green is polarized perpendicularly to the Red and Green

Conclusions Classroom projectors create images from three color regions of polarized light (RGB) Using the projector and inexpensive spectral glasses you can demonstrate color mixing. Polarization of light can be demonstrated from the different polarizations of the light

Pictures were taken by placing the spectral glasses on the front of a digital camera