Yesterday Chase posted a fairly vanilla writeup on Beacon of Light (BoL) best practices, which is probably fairly useful to his target audience - brand new Holy Paladins. He covers the basics of putting BoL on the tank, or yourself, or switching for things like Bonestorm - but he forgot one little caveat that goes with Beacon of Light. Unfortunately, it's a big one.
Haste vs. Damage
As a Holy Paladin I'm constantly slamming as much haste onto my paper doll as I can - to the point where I even passed up a 277 upgrade the other day because I'd lose 80 haste in the process. My Holy Lights are pushing 1.2 seconds, and I'm dangerously close to being over 1000 haste. Between my own CDs and a pocket innervate - I can destroy any content without fear of mana or my target dying. I guarantee that unless my tank gets one shot, there's nothing out there that will take them down. There just isn't a boss that can out damage my Holy Light spam (again, short of one shots) - providing all I have to do is stand in one place and heal one target.
Unfortunately, I have more to worry about than just a single tank. I generally am covering at least both tanks, and providing backup healing for the raid. I'm keeping an eye on environmental damage, Valk's, flying ooze balls, etc. This means I have to occasionally move or shift my healing, which means my perfect stream of 24k HL bombs gets interrupted. It also means that I occasionally have to rely on some of my other tools to get me through the night.
Enter the Beacon
BoL was a great addition to our healing arsenal, and I can't count all the ways that I revel in its deliciousness and awesomeness. Healing the party/raid while having BoL on myself (and just ignoring environmental damage). Laughing in PvP while keeping everyone alive (until that shaman/priest show up and purge/dispell it off me). Mocking healers who struggle to keep two tanks alive on Blood Queen.
Until that is, this happens.
Awesome McAwesomsacue tank has died.
WTF? How on Earth did that happen? No special abilities were used, I had BoL on them - I mean, there's no reason why they should have just gotten turned into a plate pancake. My heals can't miss (although I have done things like BoP the tank by accident), he's well within the 60yd range of well - everyone, and the person I was healing is alive! How is this even remotely possible?
Pulling out the death log, I see something horrifying. While the tank was sitting at around 60% for two seconds, there's a 1.75 sec gap between heals landing. This can't be possible, I'm mashing the HL key like my life depends on it, and my cast time is sitting near 1.2 seconds. My Judgement was still up, BoL was up, hell even Sacred Shield was up. This death was unpossible! Now I'm left standing here trying to explain how I just let a tank die on H-LK (or worse, trash) when I'm supposed to be Hasty McHasterson the great Pally healer. Guess that Val'anyr isn't really getting it done eh?
The hidden killer
In reality, what just killed my tank was the inherent lag that takes place in a BoL heal. As best as I can figure (from parsing logs and checking EJ), is that the heal actually has to register on your target before the system will pass the heal on to your BoL target. From a programming point this makes perfect sense, but it does get a little aggravating when you watch your BoL target get folded because the heal didn't get there in time. This means that all the haste we're stacking, will still result in your HL taking about 2 seconds to land every single time.
If this isn't a selling point for more haste on your gear, I don't know what is. Every single cast you put out will take about .5 sec longer to hit your BoL target. That's about the difference between having a judgment up or not - something we definitely strive for.
Avoiding this gib
There's a couple of ways to get around this little bit of lag accidentally interrupting your perfect string of awesomenss, and thereby avoiding the ire of your party/raid.
Know the encounter
This should go without saying, but you need to know the encounter. While a lot of this will come with experience, you should never be surprised when something happens during a fight. Let's face it, 95% of the encounters we face are so scripted that we have a wide variety of mods and addons to run timers for us. You know when that first Mark is going out, you know when Defile is coming, and you KNOW that Soul Reaper is about to hit your tank for Texa$.
Know your tanks
Right behind knowing the encounter, because in a PuG knowing the encounter is more realistic, is knowing the tanks that you're working with. Start cataloging their survivability. Are they taking a lot of damage on trash? Did you find yourself reaching for additional CDs on the first boss? Keep a mental log and use past experiences to prepare you for the upcoming encounter. While the odds of every PUG tank you heal using ORA2 or some other addon that will let you know when they've used their defensive cooldowns, you should be on the lookout for it if you can.
Heal the BoL target
That's right - there's nothing that says you can't switch to the BoL target when you need to. While it's certainly not ideal, neither is losing the target to an internal lag mechanic that you can't fix. This is something I'll do during H-LK. Even though I have BoL on the LK tank, unless someone is in immediate danger of dying, I'll heal the LK tank directly during a Soul Reaper. We had enough problems on this fight when we were working on it. This was a situation I could control, and I wasn't going to pass it up (obviously if Infest is running rampant, I don't have this option).
Change your BoL target
This comes with experience, and knowing where your heals need to go. After losing the Shambling Horror tank to BoL lag a few times, I swapped BoL to the LK tank and healed the Horror tank instead. Problem solved - except for when he'd eat a 70k+ shockwave. Sry:(
This also comes into play on fights like H-Sindragosa. During Phase 1 I'll keep the tank beaconed in case I need to touch the raid, but I generally just heal the tank directly (see the point above). During Pase 2 I put BoL on myself and just heal the tanks for all I'm worth. I rely on HL splash to cover the raid when I have to drop my stacks, but this method lets me build up 10+ stacks of the mystic buffet (though that does make me pucker up).
Communicate with your other healers and the tanks
I put this last, but it's really one of the most important aspects. Working with your tanks and other healers for coverage in heavy damage situations, or to coordinate cooldowns, can mean the difference between a spectacular wipe (where it just says LOLOLOLOL@U in the damage log) and that clutch downing. Rarely is the weight of the entire raid on your shoulders, though it often feels that way.
BoL is an amazing tool, and one of the most powerful spells in our arsenal. No other healer can provide the sheer throughput that we can using HL/BoL on multiple targets, though druids can rack up some impressive HoT stacks. BoL isn't a cure all though, you can't simply slap BoL on your MT and then forget about them. Part of improving as a player is looking at all the little things that have taken place in a raid in finding ways to counter them. Recognizing that your BoL target will be slightly behind in healing received means you may have to keep healing, even if their damage intake is low.
Oh, and stack on more haste.