King's Fall Raid (the one with achievements) - Yes, you need to be around 290 Light for normal and 305 for hard.
Crota's End - level 34 is recommended, but you could hold your own around 30-32.
Vault Of Glass - level 26, I think.
Everything scales once you are above that, so as a level 40, I'm brought down to 2 levels above the enemies (I do 50% extra damage and take 50% less damage) - under leveled is the opposite (you dish half damage and take double damage) and if you are greater than two levels below (i.e. Level 30 trying to shoot a Level 33 - they are IMMUNE)
Still makes the old raids challenging, as you are not unkillable, but you get more room for error. (Except when the game mechanic triggers an auto-fail)
Light level doesn't matter until you get to Level 40 - because then you can buy vendor gear which will bring you up to around LIGHT 280.
Finally - you will get new items around or slightly above your current light level - so always maximize light before decoding engrams - open 1 item, if its better - equip it, the decode the next. This works so well for the 200 to 280 climb and will work the same for the climb from 335 (current light cap) to 380 (Rise Of Iron levels - 400 will be the cap).