What's the difference between Design 50 and Chroma 50? They sound the same, have nearly same CRI, and same color temperature.
And what about Vita-Lite?

They are the same. At least, they are meant to have similar characteristics. There may be some minor differences in the chemical composition of the phosphor, but in the end they are meant to serve the same purpose.

Newer Vita-Lites are rebranded Sylvania DSGN50's.

What about older Vita-Lites?

They're different because they were made by Duro-Test, but again, serve the same purpose.