New Stuff

1. Diffraction in a TV Screen

Recently my wife pointed out the interesting reflection of a pendant ceiling light in the screen of an LG TV. The light is a “cool white” compact fluorescent bulb. After very little success in googling for an explanation I’m still puzzled as to how the twin diffraction patterns are generated. If anyone knows what is going on please let me know!
LG TV screen diffraction

2. Total Internal Reflection used in an Optical Mouse
The piece of plastic pictured below has been removed from an optical mouse. This clear plastic insert has a small vertical lens that collimates light from a LED. The path of the light is changed twice by total internal reflection and finally spread onto the surface that the mouse is placed on.
clear plastic refraction/reflection insert
The optical sensor chip in the mouse shown below is positioned above the plastic insert’s horizontally mounted lens and takes images of the surface light pattern about 1500 times a second.
Top side of mouse PCBUnderside of mouse PCB
On this last photo I have drawn the approximate path of light rays from the LED through the plastic.
Plastic Insert Showing TIR