How many lights can be wired to one switch?
A 120 volt, 15 ampere circuit can provide 1800 watts (unless it's a "continuous load", then only 1440 watts). I'd guess that a "normal bulb", is a 60 watt incandescent bulb.  Which means you can have up to 30 bulbs on a 15 ampere circuit (likely a bit less to compensate for losses elsewhere in the circuit).

120 volts * 15 amperes = 1800 watts
1800 watts / 60 watts = 30 bulbs

However, the National Electrical Code says that "An outlet supplying luminaire(s) shall be calculated based on the maximum volt-ampere rating of the equipment and lamps for which the luminaire(s) is rated." (220.14(D)). So you'll have to check the rating on the fixtures you're installing, and do the calculations based on those values.

Having said all that... You should have no problem supplying 8 light fixtures from a single 120 volt 15 ampere circuit, unless the fixtures have four or five bulbs each.