You overdid it on the spray and also note spraying lights on can cause the leaves to get burnt too. It's not the end of the world for them, they'll bounce back and new growth won't be fried, let it grow a bit and pluck away the defected leaves.
General dosing of Epsom Salts in gardening is 1 teaspoon/gal or 1/4 teaspoon/liter
p.s make sure you're using PURE epsom salt (Magnesium sulfate) with no scents/additives.