In reply to 19G:
Lighting up the crag sounds a bit full on, hardly in the spirit of adventure which it sounds like you're after & productive of vast amounts of light pollution! It wouldn't work on bigger cliffs either, unless your a film company I guess.
Having deliberately done a number of winter routes in the dark (Welsh winters being notoriously fickle & short lived in recent years) head-torches are highly recommended but as noted earlier not always needed. In good moonlight you might not need a torch & as you rightly point out they ruin your eyes' natural adjustment. That said you never know if that natural light will be there. It would also be a good idea to carry a spare head-torch as I can remember a number of times either my partner's or my torch has malfunctioned! Glow sticks would be pointless with head-torches.
Other points you might want to consider:
- Go with someone else; durh.
- Climbing well within your grade and at a familiar venue would be sensible (if not obvious) suggestions, especially if the descent is complex (you mention the Ben).
- If you're in the mountains I assume you can navigate with map & compass, because you'll need to.
- Take an extra layer, gloves & a hat: it gets cold belaying at night.
- Tell someone else where you're going & an ETA home.
If that all sounds like overkill bear in mind what will happen if it goes pear-shaped & who'll have to find you.
I'd recommend it, it's great fun & a real test of all your skills as a climber & mountaineer. As some of the folk have alluded to above, it's also great practice for those long days in Scotland & the Alps, when you'll be better prepared physically & mentally for the challenge.
Mwynhewch/Enjoy