SPF 30 blocks approximately 97 percent of UVB rays. What matters more than the SPF number is consistent daily application. Many people apply SPF only on sunny days, which misses the cumulative daily exposure through windows and during commutes.
For Indian skin, physical sunscreens containing zinc oxide or titanium dioxide are often better tolerated and less likely to cause sensitivity reactions. Reapplication every two hours during extended outdoor time is necessary.