I think that, like Oliver said, you're probably short of light.

From everything I've been able to read and/or test even the "leafy greens" like lettuce need a bare minimum of 25w per square-foot for 16 hours a day (or 50w per square-foot for 8 hours a day would be the same amount of light-hours).

With 20w or less per square foot you need 20+ hours of light per day; but then some plants want a "dark" period which could only be 3 - 4 hours in that case.

Just for an inexpensive "test" you could try pointing a halogen flood light at your grow bed for a week... the PAR meter (the "good" light wavelengths) goes through the roof - even a couple feet below the 110w GE halogen floods we have in the building. It's like 10x the PAR reading of the T-5's but from much further away.