The screen on your laptop suddenly dims while you're using it. You increased the brightness to its maximum setting. Before it faded, I was perplexed as to why it had abruptly altered. After you've...

The screen on your laptop suddenly dims while you're using it. You increased the brightness to its maximum setting.

Before it faded, I was perplexed as to why it had abruptly altered. After you've re-set the brightness,

You keep working at the maximum setting. What might be the source of the screen's dimming?