no i dont think it directly effects output. but the shape of the light will effect how much of those lumens reach the plant. if i am correct, the elongated CFLs are the best, especially if you are able to hang it horizontally above the plant. Reflectors would also obviously increase the efficiency. So althought the shape/length doesnt determine lumen output, it would be wise to find the most effective way of getting the most light possible going towards the plant.

JPG