Lumens
The light intensity produced by commercial growing lights is usually listed in lumens. A lumen measures the amount of light that can be perceived by the human eye. One lumen equals 12.56 foot-candles. Light becomes more intense with an increase in lumens, which usually leads plants to grow more vigorously.
Light Intensity and Photosynthesis
As the intensity of light increases from around 100 foot-candles to about 2,500 foot-candles, photosynthesis in most plants generally increases in a straight line; as the intensity of light becomes more intense, plants grow more. Plants that use sunlight efficiently can increase their rate of photosynthesis with light of up to 10,000 foot-candles. A lack of light is a major reason why plants do poorly. The leaves of plants growing in low light intensity will scorch if they are moved into bright sunlight. As the protective wax content of their leaves increases, the plants will more easily tolerate the sun.
Read more: Relationship Between Plant Growth & Light Intensity | Garden Guides
http://www.gardenguides.com/131549-relationship-between-plant-growth-light-intensity.html#ixzz2jmWbfTbY .
the grows with the t-5s I have done(veg only),gives me very good growth for 30 days from seed,at that point I switch to 2 400 mh.i have not flower out a plant with just t-5s,dont need to.
my flower room has 3 hps,and one 2ft t-5..
i feel that one t-5 gives me all the blue I need.