. . . for me: 12 hours on nights 2 and 3 (10 hours sleeping), aiming to finish at sunset on Wednesday (Sunday 1830 start). My (separate battery 4.4Ahc 252g) light (130g) will run for 24 hours on low or 5 hours on high. I will carry one spare battery, and not expect to use it.
Post ride 'debrief'
Chinese '1000 lumen' job (130g) with separate 'Magicshine' battery, rated at 4.4Ahc (233g), and back-up smaller (2.6Ahc) battery (133g). A 'be seen' mini light (Topeak Whitelite II with 2 x CR2032 batteries) as well. Main light has low (1/3ish) and full options. 'Low' offers enough light mostly. Fast downhills with complications when 'on the front' require 'full' (also used as a 'signal' when another rider's been on the front for 'too long'. Bench testing achieved 24+ hours on low. No plan to recharge battery though did carry mains charger (57g) and continental adaptor (23g).
Day 1 1830 start.
2100: gilet and 'be seen' light on at pop-up water refill stop in Senonches (28kph average). In train and passing nearly all the time. Occasional use of main light on low. Fougeres @ 7am for lights and gilet off. (So
10 hours of light various).
Day 2 arrive Carhaix before 9pm and stayed with long sleep for 7 hours.
Day 3: Depart Carhaix 4am ish and so
3 hours light mostly alone or leading to Brest (climbing Roc T a lasting memory with the 80 hour guys streaming past downhill and ahead a 'staircase to heaven' of PBP gilets jaunes). Rode into the night (so lighting from 9pm till 2am arrival at Tinteniac) -
5 hours use of main light on low with occasional 'full' use.
Day 4: Post dawn start (after 6hours stop and long sleep). Too much sleep including 2 hour zeds each day meant I would need to ride into the last night as opposed to hope to finish by Day 4 sunset (75 hours).
So into the dark before Mortagne - and pressed on to Dreux for just after 2am:
5 hours light, slighter higher percentage on high as 'on the front' or alone (minimal) on the Perche downhills. Light/battery went 'red' before Senonches so stopped at pop-up there (about 1am) to change to 'spare' battery (and soup).
Day 5 am: After 4 hours (3 sleeping) at Dreux set off at 6:30 so
an hour's light required.
Total hours of riding when light required - 24. Entirely content with planned provision, including carriage of spare battery.