Infrared

Infrared or IR is the name for light outside the human-visible color-light-spectrum just below red. It is often used as a means of wireless line-of-site communication such as a TV remote control.

Many electronic optical sensors such as CCDs found in web cameras, are very sensitive to IR light, but have a filter in place to filter it out, so it will look more like what the human eye sees.

Fortunately, this filter is often easily removed from inexpensive web cameras as in this example.