I have a 4 tube- 48 inch fixture (fluorescent) with full specrum light tubes. Is this light bright enough to grow mini roses?
The short answer is yes.
However, you will have to be on the lookout for Spider Mites and provide air movement to limit/prevent Powdery Mildew under lights. But yes, it can be done. You will have best success if you select the very smallest varieties you can find, such as 'Cinderella', 'Tom Thumb', 'Si', 'Yellow Bantam', 'Trinket' etc.
See link below for a full online eBook about caring for miniature roses.
Here is a link that might be useful: All About Miniature Roses