To answer this question, you need to answer some questions, like the height of the garage. It would also help to know:
- interior finish/color
- what you plan on doing in the garage
Ceiling height drives fixture type (hi or low bay - bare fixtures or fixtures with reflectors)
Color and finish of the interior provides an idea of how much light will reflect in the space versus being absorbed.
Tasks drive how much light you want. The finer the task, the more light you need.
http://www.engineeringtoolbox.com/light-level-rooms-d_708.html
Answer these questions and then you can use a lighting calculator like the one here
http://www.gelighting.com/LightingW...sistant-toolkit/lighting-layout-estimator.jsp to figure out how many lights of a given type/specification you'll need to light your space to the desired level. Adjustments to the number of lights you need, depend on the interior color and how much reflectivity you want to attribute to the ceiling or fixture reflectors. In general, the lower the ceiling and the whiter the interior color the less you need to adjust the output of the lighting calculator for ceiling or absorption loss.
You'll also want to give some consideration to the temperature (color) of the lighting. Warmer lighting (yellower) has a color temperature below 5000 K. Day light color is generally 5000-6500K. The higher the color temperature the harsher the lighting.
Other factors to consider would be cost to buy, cost to operate, cost to maintain, cold temperature performance.
Personally, I went with a 100 lumen target for my all white interior 24x48x15 garage with an assumption of no reflected light from the all the white ceiling using bare fixtures, and went with eighty eight 4 foot 6500K T8 bulbs. Since the ceiling does reflect some light, I probably end up with more like 150 lumens. To ensure no dark spots, I arranged the lights in four 44 foot long rows of 2 bulb bare fixtures. I chose this layout to minimize the number of bulbs that get blocked when the garage doors are opened. As you might suspect, the type of fixtures you elect to use need to be factored into how you want to lay out your lighting.
Of course, you can also back off on the amount of lighting you install in a garage if you intend to use work lamps instead of fixed lighting to light for specific tasks.
