|A remote control||A Digital camera with a screen, or a phone camera.|
Look at the end of the remote control and press the buttons, do you see anything?
Now point it at the camera and press buttons while looking at the screen of the camera, does the camera see anything?
You should find that you can't see anything special happening when you press the buttons, but the camera will see a bright blue or purple light flashing at the end of the remote control.
|What you see||What the camera sees|
The remote control communicates with your TV, stereo etc. by flashing a light in special patterns, a bit like morse code. So whenever you press a button the light in the end of the remote will flash. However it flashes in a colour of light called infra red, which you can't see, but your digital camera can, so it sees a flashing light.
Although your eyes can see all the colours of the rainbow from red to violet, that doesn't mean that there aren't more. In fact you can only see a tiny proportion of the actual colours of light.
Just beyond the violet end there is ultra violet light, which is responsible for giving you a suntan, and beyond that X-rays and then gamma rays. Beyond the colour red there is a region called the infra red. Infra red is a large region, and your remote works by flashing a light with a colour just into the infra red, which is called the 'near infra red'.
Your digital camera is sensitive to this infra red light, and although the manufacturers try to filter it out, some still gets through so your camera can see the communications of your remote control.