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This page covers components which emit or detect light, or change their appearance under the control of an electrical input: how to recognise them and understand how thy might fail.

Summary

Of all our senses, sight is our richest source of information about the world around us. Naturally, then, this is often the best way in which electronic devices can communicate with us. This can be through simple indicator lights through to highly complex large format diplay screens, and can embody several different technologies. Conversly, our gadgets often need to detect light, whether just to detect when a beam has been interrupted, for example by closing a lid, or in order to image a scene as in a camera. Again, several principles are used across different devices.

In total, this amounts to a fair number of different types of component, but it's generally easy to identify them, to understand what they're supoosed to be doing, and whether they are indeed doing it.

Emitters of light

LEDs

Discrete, COB, IR/UV

Photo-sensors

Light level, Transmissive, reflective, colour temerature

Displays

7 segment, dot-matrix

And now ...

... you might like to continue by reading about Passive components.