Running a Light Paladin with 105% bonus light damage. Casting Sacred Flame verses a Dark Enemy does not pick up the bonus light damage, only the bonus included for Sacred Flame text.
Base damage for my Sacred Flame was 55,827. Casting verses a dark enemy yielded 86,531 damage. (55,827 * 1.55 = 86,531)
I would have expected 177,390 (55,827 * 2.05 * 1.55) for the multiplicative bonus.
I have more testing to see if Sacred Flame is just not picking up the bonus light damage from my gear against non dark enemies.