All will be REVEALED!!1! ... tomorrow. That was really, really, really exhausting.
Okay, tomorrow is here! Although it kills me to do this, I'm going to bow to LordRaahl's wishes and leave you all in the dark. No, wait, that's not right—I'm going to give you a TL;DR version, which actually kills me more.
TL;DR: Faith in the Light is commonly misunderstood as a flat 30% buff that does some weird stuff; it's commonly accepted among more knowledgeable players as a 30% buff that scales with attack speed. In truth, however, it gives you an extra range of Holy damage. The low end of this range is 25% of your average weapon damage, and the upper end is 35%. (You can think of these as an extra +Minimum Damage affix and an extra +Maximum Damage affix, with the caveat that it's Holy damage and thus not affected by the Adds X% to <Elemental> Damage affix.) Both of these figures scale with attack speed. The net result, which is simply the average of these two figures, shows up on your character sheet DPS as a 30% bonus, scaled to your attack speed. The min/max bonuses explain odd results when using min=max weapons.
If you want the full story, see below. Word of warning: some of this thread is a bit heated! If you're just interested in the mechanics, stick with post #1; if you want some drama and brought your popcorn, keep reading. Everybody has calmed down as of this writing, and we're all adults here, so we're just moving on.
In the course of attempting to understand some of the mechanics of this game, I, like many players who have come before me, have done a lot of testing. Much of that testing has been done with white weapons and min-damage rings that equalize the minimum and maximum damage, thereby creating the perfect testing weapon: one that delivers the same damage with every swing, adjusting for crits. (I didn't come up with this method, but I wish I knew who did. It's invaluable.)
Nearly every monk skill made sense except one: Faith in the Light. The bonus doesn't show up in the Details tab in the character sheet, and the boost to the in-game DPS almost never matches the tooltip's 30% claim. But I needed to know—partly so I could make a more informed choice about the value of certain skills, but, even more importantly, because I needed that information for a spreadsheet I'm working on for the monk community. Helping players figure out their real DPS won't work very well if one of the most commonly used skills can't be accurately measured.
Eventually, I was able to figure out what is currently an open secret: the bonus scales with attack speed. In other words, if you are using a 1.40 fist, a shield, and an +8% IAS, you have an attack speed of 1.512, which means that your FitL buff is 0.3 times 1.512, or 0.4536.
Less well-known, perhaps, is that the bonus is based on the active weapon. This applies only to dual-wielders, but it means that you will get two different sets of bonuses when you cast FitL, depending on which weapon is active when you cast it. For example, consider these two weapons:
- Fist 1: 639.04 average damage, 1.40 APS (1.61 with DW IAS bonus)
- Fist 2: 612.39 average damage, 1.554 APS (1.7871 with DW IAS bonus)
If you activate FitL with Fist 1 active, the bonus (which I'll treat as 30% for now for simplicity) will be equal to the following:
639.04 x 0.3 x 1.61 = 308.66 (rounded)
If you activate FitL with Fist 2 active, you'll get this bonus instead:
612.39 x 0.3 x 1.7871 = 328.32 (rounded)
This is especially important if you aim to have the most effective weapon active when you cast Sweeping Wind. In this case, the difference is negligible, as the two weapons are separated by less than 1%: 948 for the first weapon against 941 for the second, essentially. For many users, however, this information could flip their choice of active weapon to the other hand because of the scaling bonus. For example, boosting the damage of Fist 2 by 14 points would make it just slightly better for Sweeping Wind even though many players would consider Fist 1 the clear choice because it has a higher average damage.
In testing FitL with my normal gear and with mi=max white weapons, I came upon a result I couldn't explain: the damage wasn't consistent. I had read suggestions—I think Druin might have made one of them—that the skill grants a range of damage as a bonus, and that made sense. But I couldn't figure out why a 30% tooltip buff would routinely dip below a 30% damage boost. In researching the issue, I came across this post by Thaya at diablofans.com:
The piece that helped the most was this:
"I went to Normal mode and got myself some random weapon with 15 DPS and 9-16 damage range, 1.2 APS. I also equipped a +9 minimum damage necklace, so effectively my min and max damage were equal (confirmed in tooltip for "attack": 18-18). My total APS was 1.46. Every time I hit mobs I did 268 damage, I must've hit like 30 times just to be sure."
I had done plenty of min=max testing but hadn't seen a tooltip like this, so I went looking for it. I couldn't find it anywhere—until I remembered that I could vacate my primary attack on my left-mouse button by assigning the same skill to a different button.
Voila! Instant "attack tooltip":
That's a look at my Shenlong's Fist of Legend, which has a tooltip damage range of 436–842. Testing has revealed that the attack tooltip always truncates the numbers, unlike the tooltip damage range, which rounds them. This backs up what I said about calculating a weapon's true damage range here:
Equipping a two-handed weapon doing 9–11 damage with a +20 Minimum Damage ring and then activating FitL produced this:
That picture verified that FitL was adding a range of bonus damage, not a single number. At that point, really, it was just a matter of staring at the numbers, thinking about the problem, and finally coming upon the solution. I knew that the average had to be 30%, scaled by attack speed, which suggested one of two options:
1. A scaled range based on concrete high and low percentages
2. A scaled 30%, modified by some set figure (e.g., a scaled 30%, +/-5%)
Tweaking a few items—especially IAS items—eventually revealed the answer. My final test was to equip my Burning Axe of Sankis, with its Adds 6% to Fire Damage affix, another weapon, an IAS helm, and a couple rings, and then to turn on Eirena's Focused Mind buff. I calculated the Axe's damage range, including rings, as 499.7486–917.8898, which D3 backed up as follows:
If my calculations were correct, I only needed to use the average damage to calculate the scaled minimum and maximum bonuses.
499.7486 + 917.8898
x 0.25 (25% bonus)
x 1.33 (basic attack speed with Focused Mind)
x 1.23 (DW bonus plus 8% IAS on helm)
289.88933232 (scaled 25% bonus)
x 35/25 (gets us to 35% the quick way)
Expected damage range with FitL buff:
Min damage = 499.7486 + 289.88933232 = 789.63793232
Max. damage = 917.8898 + 405.845065248 = 1,323.734865248
Accounting for the attack tooltip's truncation of the displayed value, I should expect a range of 789–1323.
And here's the result:
This behavior accounts for values that vary from the expected return of a 30% bonus scaled by APS. I searched Google for confirmation of these results, expecting to find that I had wasted my time researching something that was already published, but I didn't find any explanation of this mechanic beyond "it's a 30% bonus that scales with attack speed." Maybe my search-fu is weak, but I think this is the best explanation we've got right now.