how many recessed lights to a circuit?

i am interested in installing recessed lights in an unfinished basement. how many lights can i have on a circuit? is it based on wattage? is there a difference if i used 12v system?
i have read 12 devices (including receptacles) on a 15 amp circuit. i also read 2400 watts max per line. is this correct?
SaM
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I use 180 watts for load calculations for residential for each outlet or light. Max for an 15 amps circuit is 1440 watts or 80%. Max for an 20 amp circuit is 1920 watts.
Watts of the input of the transformer is what is used to calculate loads when you use LV.
Personally I like to put recessed cans on several switches. I like multiple levels of lighting for different tasks. Recessed cans in the basement can be small circle of light unless your ceiling is more than 8 feet. Every manufacture has lighting diagrams that will help in the design of the installation. I like wall washers, 20 inches away from the wall so that I can light up the walls and not just the floor. Gives a good amount of light bouncing around with out the shadows that can happen with down lights.
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120 * 15 = 1800 watts resistive, don't put a motor on this 120 * 20 = 2400 watts resistive, likewise
Don't put receptacles on your light circuit if you can possibly avoid it. Also, consider compact fluorescent bulbs. They're more expensive to purchase, but 18 watts per bulb pays for itself here in ConEd land.
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Your 2400 watts figure is for the maximum load on a 20a circuit. It's 1800 watts for a 15a circuit.
You could load up to 80% and that's 1440 watts on a 15a circuit, or 9 150 watt recessed lights. You have to allow for the maximum wattage *allowed* in the lights you purchased, not the wattage you *intend* to use. Many recessed lights are rated for 150 watts, but smaller units and other decorative accessories like "eyeballs" and "wall washer" trims usually reduce the actual *allowable* wattage.
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