Testing toon with Master of Light
Divine Punishment average damge = 100ish per tick
Searing Light average damage = 220ish per cast
Sunbolt average damage = 1050ish per cast
Feat swapping tough in place of master of light
Divine Punishment average damage = 80ish per tick
Searing Light average damage = 109 per cast
Sunbolt average damage = 634ish per cast
Conclusion: Master of Light feat is affecting Divine Punishment, Searing Light, and Sunbolt.
Conclusion: Since Divine Punishment is only gaining +5 damage per tick, a 25% gain is likely correct, as is the double damage on Searing Light, and additional damage on Sunbolt (without doing serious math, all looks ok to me).