What is the appropriate amount of light for reading?

Question

Such as when you are studying or reading late at night

Answer 1

Basically, unless it's causing glare, it's near impossible to overdo it.

The ideal light is close coming from over the shoulder.

This means the light is on the page, not in your eyes, and slightly offset to avoid reflections from shiny pages.

If the light is close to your shoulder a 40w bulb (or its equivalent in low energy bulbs) is fine.  But the distance from the bulb to the page is more important than the wattage.

That 40w on the shoulder will out-perform 150w in the ceiling.

Spotlights, with a reduced light spread, are not quite so distance-critical, but the effect is stil there.