For those experienced enough, it has not necessary to bother with 4 foot-candle readings. They can tell by the appearance of the plants if they are getting the suitable amount of light, and you can learn to judge this too. If plants need more foot-candles to grow to better proportions and to flower profusely, these plants can simply be put closer to the lights or the lights can be burned longer every day. Foot-candles are meaningless as a guide to the effectiveness of agricultural lamps. Light meters measure all light, and the agricultural lamps are lacking in green and yellow spectrum. The spectral energy distribution of these lamps is measured in laboratories using a spectro-radiometer. In our gardens we measure the spectral energy through the condition of our plants, moving them closer or farther from the lights as growth indicates.
Other resources on this topic:
Basic Fluorescent Light Setups for Indoor Gardening
How Much Light Does Your Indoor Garden Need?
Plant Lights For Your Office Indoor Garden