What species are you working with?  You may want to consider editing your question to include this species and list it as a topic so researchers can find this question.

White Light, Blue Light, Red Light and Far Red light are directly involved in modulating the plant hormone response and synthesis in plants and as a consequence to influence the leaf number. Also, you have to take into account the plant specie and and cultivar. I suggest to play with appropriate combination of the different light types.

Regards

white light is rich in red light , which is important not only for photosynthesis, but also play a very important role in photo morphogenesis , which is responsible for normal leaf development, as under such conditions  the phytochrome is in the Pfr form, and it is now well established that this form of phytochrome plays an important role in gene expression leading to increase in leaf number. As for blue light.there are of course blue light receptors in plants, and blue light plays important role in a number of responses, such as photo tropism  ,stem elongation, and stomata l movement, and these will in turn affect leaf number indirectly .