vampires had reached the point where their bodies wouldn't be destroyed, many of the test subjects exposed to more than ten minutes of direct sunlight were driven insane by pain: those exposed for even five minutes were left crippled, their regenerative abilities destroyed. No matter what treatment they later received, they never recovered.
Sunlight only affects Vampires on earth. The reason for this is unknown. But Nobles can enjoy the rising sun from other planets and celestial bodies with out it affecting them in the slightest. This sparked many to explore space.