... Project 1.Material:plastic 2.Vishay TSAL6400 LED 940nm 3.Cell LR41series Invisible IR PenIt is for the whiteboard using ... is pressed down one the tip of the IR pen ,an IR led with a wave length of 940 nm ,is ... the user press the button on the pen ,the LED light isturned on .even though human eyes can not ... see it ,when the LED light is turned on .the computer consider it as ...