“They used to use a florescent lamp(s) to light the screen. They can be replaced, but if you are not doing it yourself the labor is likely non-economic.”
WAY easier just to replace the whole LCD panel, but even then, with an old laptop, not usually worth the expense.
I hate taking laptops apart and putting them back together even more.
Inexpensive tablets seem to be the wave of the future for me for anything remotely portable.