Id say the lowest light you wanna be at for nightfall is 260. I did it with one guy at 264, another at 272, and myself at 276. So 280 light isnt required. The hardest part is when you have to jump to either side and finish the transmat because grounded is on and those wizards reck havoc ;)

Damn. I've been just chilling and doing quests casually so not a lot of light but I guess I'm gonna start grinding now...