At what level of cave training could you realistically start doing 2 hour dives?
If you're doing 2 x 1 hour dives per day, what's wrong with having a 90-minute burn time and changing batteries between dives?
If you're not going to do 2 hour dives anytime in the immediate future, why buy a light now that can handle that, for hundreds of dollars, when the tech (light and battery) is changing pretty fast and what you need could be a lot cheaper by the time you need it? Not to mention how batteries degrade over time, so buying a big, expensive battery pack that you won't actually need for a year or two means it won't even be what you paid for by the time you actually need it. And when a light that can give good output, beam angle, and adequate burn time (for a 1-hour dive - or even a fair bit longer, really, even with a 50% reserve) can be had now for well under $100, including multiple batteries?
At the intro level divers will likely do 2-3 dives a day. Dive times will range from 30-60 minutes, depending on location, SAC rate, etc. A 1 hour light will not be long enough in the event something delays exit. A 90 minute light may be OK, but sometimes people will do multiple dives without leaving the water, how are you going to change batteries then?
Here's an example:
Dive 1 and 2 - Peacock Springs.
Dive 1: Up the Olson Line towards Olson. Depth averages about 60'. Starting PSI - 3600, 1/6ths is 600 psi. You should be back on the surface with no less than 2400 PSI. It's not uncommon for an intro diver to get a 30-45 minute dive on this.
Surface interval in the basin, discussing the dive, etc. You have 2400 PSI in a set of doubles. Is it enough to do another dive? Yes, of course it is. Do you need to get out of the water to do this? No.
Dive 2: Up the peanut line. Maximum depth is 60', but for a big portion of it you're at 30' (at one point you're at 18'!). Starting PSI - 2400, 1/6ths is 400 psi. Average dive time is ~40 minutes -- this is very DOABLE.
Dive 1 time - 40 minutes. Dive 2 time - 40 minutes. Your 90 minute light is going to be at the limit assuming everything is going well.
As to the question of "why buy now?" -- my question is "why buy twice?"
While light technology does change, the high end lights aren't changing very rapidly and the price is pretty constant if you look over the past few years. A light you buy today will be useful years from now. I have a four year old Dive Rite light that is perfectly suitable for doing full cave dives today. Is it as bright as an LX25's, no, but is it suitable? Yes. And guess what, it's perfectly suitable for doing intro to cave dives too! I do not have the disposable income to throw away on mediocre crap that I will want to throw away later.
Personally, I would rather make an investment in a good light once rather than buying a mediocre light now and then buying a good light later. But that's me.
See what I did there? I used the word "investment" -- a good light is an investment in you and your diving.
2 hour dives in caves aren't uncommon once you hit the full cave level. It may be a pair of one hour dives back to back, but you don't really have the ability to swap batteries. I have no problem for those using a pair of the small backup lights and just using one on the way in and one on the way out, but much prefer a canister in that situation for ease of use. My biggest issue with the big handhelds like the LX20 from Dive Rite are just how damn big and heavy they are. It is truly exhausting using them in comparison the relatively tiny light heads on the LED canisters.
I have yet to teach a full cave class that we didn't do at least one 90 minute dive. I recently sat in on a cave CCR class where every day there was a 3 to 4 hour dive. I have a full cave class coming up in a couple of weeks that I fully expect we will get ten hours of bottom time in the cave over four days. This is just the way it is.
As for planning to swap lights during a dive, I have a huge problem with planning for a light failure as part of the operating procedure.
Let me ask, why would you never turn your light off once it's turned on? There's a reason for this, it's not as important as it was with Halogen bulbs, but there's still a reason for this.
