What breaker size is required?

Depends on where you live. Some electrical codes tell you what the maximum on a lighting breaker size is. So check with your regional code. There is a calculation that you can do to figure out the proper breaker size.

AMPS = WATTS/ VOLTS

what that means is that your total amperage will equal your watts divided by volts. If you want to use a 20 amp breaker, 40 watt light bulb (pretty standard I think) and 120 volt you would figure it out like this...and just to be on the safe side,you want to use only 80% of the breaker capacity.

Amperage (per Light)= 40/120

equals 0.33 amps per light

80% of a 20amp breaker = 16amps

now divide total amps by amps per light

16/0.33=48

so with a 20 amp breaker you could supply 48 lights with a 40watt light bulbs and still have a 20% safety margin. So there is not really a breaker that is to high, just unnecessary when you only want to put 4 lights on a breaker, go smaller.

Hope this makes sense, good luck.