So let's get down to business, what we are looking for is whether Surge of Light actually improves the dps output of a 37/27/7 Holy Fire Spec (I say Holy Fire because without it, Smite nuke numbers are low).
- You have enough haste to enable 1.33 global cooldown and 4 x smite in every holy fire DoT duration.
- Cast duration is 272 seconds (4 and half minutes non stop approximately)
- 24 cycles: 24 Holy Fire, 96 Smite, so we have a total of 120 casts.
- Ignoring damage done by other spells
- Hit capped, 2000 spellpower, 37/27/7 pure holy dps build
Top table is with SoL, bottom table is not. Blue represents "real time", orange represents "ideal time or pure dps"
The Smite glyph has a lot of limitations, the fact that holy fire DoT runs shorter than Holy Fire cooldown creates "gaps" in between casting. During these gaps, casting Smite un-glyphed is inefficient, it also reduces the effectiveness of haste, since the primary advantage of a SoL smite is that you spend only 1.33 seconds casting it instead of 1.74.
As you can see, in "Real Time", SoL dps is lower than non SoL dps, but that is perhaps compensated with filler spells such as SW:Death or Mind Blast, since 1.74 seconds normal smite won't allow you to squeeze those spells into your rotation (at least not as many).
However, if you were to assume "pure dps" calculated ignoring spell cooldown and waiting times, SoL spec will have higher dps output than non SoL build up to and until 80% critical strike rating.
Note: spreadsheet not done with easy understanding in mind, it's just a quick sum up of what I imagine the calculation should be, some columns should be ignored as they are used to check formulas and consistency.