Things You Will Need
According to the Cooperative Extension Service of Purdue University, you generally want to have 20 foot-candles of light at floor level, which means about 1/2 watt of fluorescent, or 2 watts of incandescent, shop lighting per square foot of shop space.
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Determine what size lights you're going to use, and how many bulbs are going to be in each fixture. A standard type of shop light fixture is a 48-inch two-bulb fluorescent fixture.
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Determine how many watts the fixture supports. In the case of a standard 48-inch shoplight, it will produce 80 watts of fluorescent light, 40 watts per bulb.
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Divide the wattage of each fixture by the number of recommended watts per square feet to calculate how many square feet your fixture will cover. In the case of a standard 48-inch shop light, we know from our previous calculation that it puts out 80 watts of fluorescent light, and we know that the recommendation is 1/2 watt per square foot for fluorescent lighting, so that fixture will light 160 square feet.
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Measure the floor area of your shop, multiplying the length by width in feet.
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Divide the area of your shop floor by the number of square feet that each one of your chosen fixture-type will produce to determine how many fixtures you will need. If I have a 600-square-foot shop, and I'm going to use the 48-inch fluorescent shop lights, I'll divide 600 by the 160 square feet that each light will cover, to get 3.75. With lighting, you should always round up, so I'll buy four fixtures.