Why add long fluorescent lights?

[Pinkstardust]

I looked at grow journals and I see people use an led light,and two long fluorescent lights on each side. Why not just an led light?

 

[CO Finest]

Help promote side and under growth. With led dont have the huge heat so can add extra lights when needed

 

[JJ Bones]

Yup as CO Finest says it adds supplemental lighting that is really beneficial to your plant. I've used T5 combined with LED with some nice results on personal grows.