Every holy paladin has limits
In a hypothetical 5-minute encounter, you can only cast a certain number of spells. Assuming that your global cooldown is around 1.25 seconds, which is common for a Firelands-geared holy paladin, you can cast a maximum of 240 spells in 5 minutes, or about 48 spells a minute. I will tell you now that you'll never actually be able to cast 48 spells per minute for an entire encounter, because you would be out of mana before it was over. You'll find yourself GCD-bound when using you cheap spells and mana-bound when using your expensive spells, and balancing the two becomes your first priority. Assuming that we use our crucial Judgement and Holy Shock spells on cooldown, we're actually reduced to only 30 productive global cooldowns per minute.
How many spells can we cast?
While it's impossible for me to tell you exactly how much mana you have at your disposal on a given fight, I can make an educated guess. I started by taking my own buffed maximum mana values and then using World of Logs to add in all of the mana regeneration that I see in a given fight. A typical holy paladin will have between 400,000 and 500,000 mana to spend over the course of a 5-minute engagement, assuming excellent Judgement and Divine Plea usage and standard raid buffs. The approximately 450k figure assumes that you spend all of your starting mana and that you end the encounter with no mana remaining, and also factors in our spirit-based Meditation regeneration that doesn't show up on WoL.
Based on these numbers, you can only cast about 50 Divine Lights in the average 5-minute fight. If we're looking solely at our casting speed, we could cast all 50 of those Divine Lights in a mere 2 minutes, although obviously that doesn't actually work since it takes us a full 5 minutes to generate the 450k figure we're discussing. The point is that we can only really dole out about 10 Divine Lights per minute, and even then we'll end the fight nearly out of mana. You could be standing around half of the time and yet still end up out of mana at the end of the encounter.
I hear plenty of heroic raiders claiming that the game's most difficult fights require nonstop Divine Light spam, but it's simply not true. The header image for this article is a comparison of the top holy paladin parses for the 25-man heroic modes of Shannox, Baleroc, and Majordomo Staghelm. The best holy paladin parse from heroic Baleroc shows that our hero only used Divine Light a total of 24 times in a 6-minute fight, which is hardly what I would call spamming.
Similarly, the top parsing paladin facing heroic Shannox cast a total of 32 Divine Lights over his 3-minute fight, for a rough total of 11 per minute. You can see that while Divine Light is going to make up the bulk of our healing done, we actually have to discriminate about when we choose to unleash our most powerful heal. Do you want to use your Divine Lights to handle the raid damage now or the tank damage later?
Holy Light is still our bread and butter
Holy Light, on the other hand, can be cast almost indefinitely. Based on our limited mana pool, we can toss out around 150 Holy Lights per 5-minute encounter. Our earlier estimate of 30 free GCDs per minute, we see that we could actually spend every free GCD casting Holy Light and we'd end the encounter right at zero mana, and that's assuming we had the astronomical amount of haste required to bring Holy Light's cast time down to the GCD.
It's important to note that while we could theoretically cast Holy Light with every global, that would involve not using any Divine Lights. For every three Holy Lights that you cast, you lose out on a potential Divine Light cast. Holy Light is great for tending to lightly wounded players, but we have to realize that there is a very real cost to our mana pool for doing so. If you spend half of an encounter spamming Holy Light, you've cut your possible Divine Light pool in half as well. The other side of the coin is that if we're in a period of light damage, we can easily cast a few Holy Lights and then allow our mana to regenerate back to full, which resets our potential healing counters back to zero.
Every time we cast a spell, we're taking mana away from that overall encounter mana pool. While you might want to pop a Holy Radiance to give yourself an extra speed boost to avoid some obstacle, there is a tangible cost to casting HR. You have to realize that the mana cost of HR is equivalent to a Divine Light and a Holy Light combined, which means you can cast two fewer healing spells over the rest of the encounter. Divine Protection provides us with the same speed boost but for less than 10% of the mana cost, yet I still see holy paladins using HR as their own personal Sprint anyway.
Cheating the limits
Every healer is limited by their overall mana and GCDs, but paladins have a few clever tricks for skirting the rules. Beacon of Light allows us to double our Holy Light casts and boost our Divine Light casts by 50% when we cast them on off-Beacon targets, which greatly increases the amount of healing we can get done with those 50 Divine Lights or 150 Holy Lights. Because we're also casting Holy Shock on cooldown, we build up 3 holy power points at least every 18 seconds, which means we can toss in an extra Word of Glory or Light of Dawn a few times a minute as well. Using Holy Shock and the holy power releases properly becomes a huge part of managing your mana as a holy paladin, as they can make up a significant part of our overall healing done.
I know that I can only cast about 20 Divine Lights per minute if I'm keeping up my Judgement and Holy Shock usage and that my mana pool plummets when doing so. When we're facing a tough boss and time is winding down, I start estimating when I can go into what I call holy firehose mode. Once we reach the point of no return, I start casting Divine Light on every wounded target non-stop, because I know that I have enough mana to last me until the fight ends. For me, if I'm near full mana and we have under a minute left, I stop choosing my spells and I start blasting out Divine Lights. There's no point in ending an encounter with extra mana, especially since all of our overhealing can provide Illuminated Healing bubbles.
The key to remember is that we have a limited number of spells we can cast per encounter, and we need to discriminate when we're choosing which spells to heal with. While a few overzealous Divine Lights might not seem so bad in the short term, it directly reduces the amount of Divine Lights you'll be able to cast over the encounter's duration. We can use Divine Light freely when facing Alysrazor, as we can quickly recover our mana during her Burnout phases. Against Beth'tilac, though, we can't afford to be missing mana entering phase 2, as we need all of the healing we can muster.
Be cognizant of each heal you cast, and ensure that you're always picking the right heal for the job. I have this thought before I cast every Divine Light: "Is this the best use of this mana?" If my answer isn't a resounding "yes," then I know I've made a mistake.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Find out just how masterful mastery healing can be, gear up with the latest gear, and learn how to PVP as a holy paladin.