What are Headlights?

The Headlights is part of the car electrics system. We have 2 associated problem symptoms connected to it.

What problems can be caused by this part?

Headlights are less powerful than usual

The headlights don't seem to be as bright as they were, they don't light up as much of the road ahead as they used to.

Headlights not coming on at all

The headlights won't switch on at all after pressing the button / turning the stalk. The rear lights and indicators appear to work ok but the headlights are not functioning at all.

We have 412 owner problems that mention the Headlights