For general garage lighting I think 10 footcandles (fc) should ok. Depending on the specific working task, it could be anywhere form 30 to 300 fc or more on the working surface. The IES lighting handbook has the fc requirements for many specific tasks. Good flourescent fixtures are hard to beat but make sure you don't have strobe effect when working with rotating machines or tools.
For example, my woodshop (table saw, radial arm saw, drill press, etc.) has about 100 fc with flourescent fixtures. This translates to about 3 to 4 watts/sf at 8' ceiling mounting height and off white paint.
What are you going to be doing in the garage? If you just park cars in there, you don't need much a bare bulb in the middle should do fine, If you want to do detailed hobby work you will need a lot more.
To get an idea of what is required for diferent tasks you need to google up lighting specifications rating different ocupations, flourescent are most common but metal halide? is used in large areas.
The suggested of having switched levels of lghting is a good one, that way you don't have light for surgery when you've just taking out the trash.
Suggested light levels (in foot candles)
Hallways or corridors 10 general area average
Work and circulation areas 30 eneral area average
Normal office work 50 (40-60) Measured at work surface
Prolonged office work 75 (55-90) Measured at work surface
Visually difficult work 100 (80-210) Measured at work surface
A rough rule of thumb is about 2 watts fluorescent per square foot of work area. This will yield light that is adequate for general work (40 to 60) any boost above that could be handled with task lighting or extra fixtures.
YMMV as the specfic conditions can influence final lighting results (ceilign height, paint color, fixture type)
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