Which word can I use to describe too much light, i.e., when I have switched on 3 bulbs while there was a need for only 1 bulb?
The light is blinding if excessive light, and not excessive power bills, is what bothers you.
The place has been overlit: it has been provided with more than the required amount of lighting (intensity), such as an overlit stadium for an all-night match.
If positive: brilliant
If negative: glaring, blinding
Excessive does it for me. The effect, if dazzling or glaring, or the power consumption, if extravagant or wasteful, might lead to different choices (q.v.), but if it's simply a matter of more light than was needed or desirable, then ...