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A light you cannot see

How Does a Remote Control Reach the Television?

A remote flashes an invisible light at the television in a pattern, and each button has a pattern of its own.

An LED at the frontIt flashes infrared,not visible lightEach button has its ownpatternA sensor in thetelevision reads it
The remote is a torch, blinking a code.

  1. Step 1 of 5

    It really is a light.

    The dark window atthe front An LED emitting justpast visible red

    Behind the dark window is an ordinary LED. It emits infrared, just past the red end of what your eyes can detect, so it looks dead while it is working.

  2. Step 2 of 5

    The message is a pattern of blinks.

    1 You press abutton2 1011 A fixed patternof on and off3 Flashed out ina fraction of asecond

    Press a button and the LED flashes a fixed sequence — long, short, short — which the television reads as a number. Each button has its own.

  3. Step 3 of 5

    A flicker rate keeps sunlight out.

    Steady sunlight Bright infrared — butnot flickeringThe remote Chopped at 38 kHz — theonly thing accepted

    Daylight is full of infrared. So the blinks themselves are chopped at around 38,000 times a second, and the sensor ignores anything not flickering at that rate.

  4. Step 4 of 5

    It needs to see the television, or a wall.

    Aimed at a wall Infrared bouncesto the sensor

    Infrared does not go through furniture, but it bounces well. Pointing a remote at the ceiling or a pale wall often works because the light reflects.

  5. Step 5 of 5

    Newer remotes use radio instead.

    Infrared Line of sight, onedirection onlyRadio Through walls, and itcan reply

    A radio remote works through cushions, doors and around corners, and can talk back — which is how a lost remote can be made to beep from the sofa.

    Point a remote at a phone camera and press a button. Most camera sensors do see infrared, so the invisible LED shows up as a flickering violet spark.

The short version

A remote control flashes an invisible infrared light in a pattern unique to each button, chopped at a rate the television's sensor knows to trust.

Try it yourself

Look at the front of a remote through a phone camera while pressing a button. You will see the flash your eyes cannot.

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