I assume you're referring to the effect of reduced cast time on +healing bonuses from gear. The amount of your bonus applied to your spell depends on the coefficient of the spell determined by: (Casting time of spell)/3.5
All instant cast spells are considered 1.5 secs for this calculation.
WoWWiki wrote:
The casting time used in the calculation should be the base cast time before effects from talents or gear are applied.
The bonus to your HL from gear is the same before and after Light's Grace talent. The talent doesn't change the amount healed by the spell itself either.
edit: clarified coefficient calculations
Edited, Jan 18th 2008 12:06pm by BlackoutCC