Linear fluorescent lamps are named according to diameter, in 1/8 's of an inch. T8 is (8/8) = 1" diameter, T12 is (12/8) = 1.5" diameter, etc. I don't hear of T10 much. I would think you'd want a 100W or, likely, even bigger incandescent to match the lumen output of a 20W fluorescent. What is the fluorescent fixture like (bare striplight? clear wraparound acrylic lens? ?) and what fixture would you have in mind for the incandescent (bare lamp? recessed potlight? ?). It can make a big difference in terms of the amount of the lumens that are delivered.
There are lighting newsgroups, if you find one of those you'll probably get lots of answers.
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