I'm a mechanic in an open pits mine way up north. Everything is dark nights are loooong in winter. Unless you're directly under a light tower you out of luck.
I've been using a Petzel Ultra Vario. 520 lumen max output. It's like having the night sun on your head. The spot feature will light up around 80-100 meters away in a focused beam.
It's fairly heavy. But has a lithium battery pack that you attach to the back. So it's fairly neutrally balanced on the helmet. It's also not cheap. Don't suffer sticker shock. It is that much better. It's a caving lamp by design.
We have all sorts or those smaller battery powered ones. All different kinds. Their all junk in comparison. I use it every single day at some point. Even inside the shop when I'm in some stupid hole on a machine. Won't do without it now.
It's also expensive, and regular SAR doesn't really need a light this burly. The new Fenix HP10 is pretty hard to beat for the money. I have one on my other helmet. I will also second the recommendation of something that takes 4xAA batteries if possible. Or at least 2. I also recommend carrying a spare 2xAA or 2xAAA small light as a backup or to give to the victim you're trying to walk out.
I have found that max lumins is not necessary for SAR work, sometimes I even go with just moonlight. The headlamp on my helmet is an older Prinsten Tech. I recently purchased a new Black Diamond Icon. It doesn't seem to be any brighter than the old one. Both have a Cree chip for the main light and multiple smaller LED's for wider pattern light. Both use common AA batteries and have multiple power output. I very seldom use full power, even with my 68 year old eyes. Of course I usually have a powerful hand held light with me for searching nooks and crannies.
I have found that a belt light is much better for seeing the rocks and terrain unevenness than a head light. The headlight at almost eye level gives no shadows to show features on the trail right in front of you. So I actually have three lights for dark nights, head light, belt light and handheld flash light....
I love my Gen 1-2 Black Diamond Storm headlamps. Don't have any experience with the new ones. Has a red filter, Wide, and spot beam. Each one is infinitely dimmable, and has a quick tap to go back to the previous setting. I have a few I have abused and used, they are still going strong. One I use in me Remote Medical pack, its seen everything you can imagine. And another I keep in my truck for feeding, checking livestock, lambing, calving at night. Hiking, camping, whatever.
I just retired my gen 1 BD Storm and got the new one. I like the "latch" ability on the new one to speed/ease the change out of batteries. I alway forget to replace the batts after the last mission and end up doing it either in the field or when getting ready at staging. I like a big swing range to dip the light, so as not to blind folks I am talking and to show me where I am walking.
A couple of dittos to some other comments: I rarely have mine set on the brightest setting, usually have it dimmed down. I also carry a Big Larry LED light clipped to the chest strap on my pack as a backup and/or to get a offset light angle when needed.
About a 50/50 split on our team on folks who carry a all-in-one vs. a separate batt pack light. I am old and every ounce counts, Never had mission where I ran out of power (unless I forgot to change out batts).
Like on a avy beacon, I don't use rechargeables, because of the abrupt power drop-off when you are at the end of the batts life. I like the tapper-off of a non-rechargeable.