When discussing the major changes that paladins saw in Cataclysm, holy power is always at the top of the list. While hunters received their pseudo-energy resource called focus and death knights had their rune system revamped, holy power was easily the most interesting mechanic that was introduced. There's no way to play a holy paladin efficiently without completely adopting holy power. The two holy power releases are both free and flexible. They only cost holy power to use, and they give us a strong instant heal and the only instant AoE heal in our toolbox.
We receive a relatively fixed amount of holy power every minute, with the biggest contributor being Holy Shock. We can only use Holy Shock about 10 times a minute, although a few of our talents help augment that number. The key concept is that holy power is a fixed resource, which means that deciding between Light of Dawn and Word of Glory becomes an important choice.
The balance between WoG and LoD
On a typical encounter, Word of Glory and Light of Dawn add up to about 15% of my total healing. The extra instant healing output is nice, but the real savings comes from not having to spend any mana on those heals. Light of Dawn has traditionally been very powerful in 25-man raids, where chances are that there are multiple wounded people in range. Word of Glory sees more use in 10-man raids, where AoE healing is not usually that big of a concern. Light of Dawn does a significant amount more healing than Word of Glory when you factor in its interaction with Beacon of Light, but Word of Glory can be used reliably when running.
While Word of Glory is good for single-target healing, Light of Dawn can actually be the preferred choice. I ran the numbers myself when first experimenting with Light of Dawn, and Kurn, a fellow holy paladin, has written up detailed calculations. By design, Light of Dawn replays 50% of its healing to our Beacon of Light target. A well-placed Light of Dawn can heal your raid for nearly 50k life and then replay a 25k heal to the Beacon target. Word of Glory, on the other hand, heals for closer to 20k to a single target, with 10k replayed through the Beacon. Clearly, Light of Dawn is the superior heal today -- but what about after patch 4.2?
WoG gets its own niche
In patch 4.2, Word of Glory is seeing a 30% buff via the holy tree's passive bonus, Walk in the Light. Word of Glory still can't compete with Light of Dawn when it comes to total healing done, but now only when the original LoD targets are wounded. LoD will transfer 25k health to the Beacon target as long as you hit all six targets (assuming you're using Glyph of LoD), but it won't heal anyone who's not injured. WoG will be healing for over 25k health to a single target, plus the extra heal from Protector of the Innocent and the 12.5k health that will be sent through the Beacon. If you only have one or two wounded targets, WoG can now surpass Light of Dawn's potency.
Light of Dawn has a long history of being both too powerful and too weak, and it has even received a few redesigns during its lifetime. The spell has had cooldowns, consumed mana, and actually caused the Holy Light/Beacon of Light nerf back in Cataclysm's early days. I like Blizzard's approach to fixing it this time, buffing the alternative ability instead of just nerfing LoD to make it worse. We now have a choice: heal the raid, or heal the tanks. The distinction between WoG and LoD has been expanded and now makes us choose what to do with our holy power.
Scoring extra holy power
I browsed the World of Logs parse from a raid a few nights ago and added up all of my holy power gains. It was an 8-boss raid, with Halfus being the only heroic we attempted. Throughout the raid, I gained 250 holy power points from Holy Shock, making it our biggest holy power source by far. Tower of Radiance, which gives us holy power when healing our Beacon target with Divine Light, came in second with 40 points. Tower of Radiance used to see a lot of use, as holy paladins would spam Holy Light on their Beacon target and then blast the raid with Light of Dawn. Now, I see most holy paladins using ToR in their single-target healing rotation, casting two Divine Lights, a Holy Shock, and then a Word of Glory.
Blessed Life, one of my favorite optional talents, gave me 35 holy power points throughout the raid. Blessed Life is interesting because it's very valuable on some encounters and worthless on others. I still think it's worth carrying around in your build, anyway. Free holy power means free healing done, and that's worth putting talent points into. Eternal Glory only yielded 22 holy power points for me, but I also only have one point in the talent, anyway. Eternal Glory has an internal CD attached to it, and so many holy paladins only toss one point in here and use the other one elsewhere.
The only other holy power source I see used is the Pursuit of Justice talent, which can be very valuable for holy paladins in PVP but not so effective in raids. Because we have a limited amount of holy power per encounter, we have to spend it right. After patch 4.2, both Word of Glory and Light of Dawn have pretty clear boundaries for usage. Maximizing your holy power release usage is incredibly effective, as it boosts your healing done while reducing your mana spent. In particular, the two-heal method abuses Word of Glory and Protector of the Innocent to help you save your mana for when you really, really need it.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Cataclysm 101 for holy paladins, study the new balance between intellect and spirit and learn how to level your new Sunwalker. Tanking is a job, DPS is a craft -- but healing is truly an art.