The trick is to roam to those lanes when you can. As lux, you should be able to clear a wave very quickly and then roam bot or top to help them get rolling. Don't be afraid to fall a few more CS behind, if you can get top rolling even though bot is throwing hard you might be able to get back into the game. If Top is able to get ahead they will be able to help you out in mid. When you see a lane falling, you have two choices. 1: Go help them and get them back into it before they get too far behind. 2: Help the other lane (lanes if jungler) get ahead so that they can counter balance the teams. In the game you described, it sounds like they were falling behind for a long time (unless they really bad/intentionally feeding and somehow fed 16 kills in under 15 minutes). When a lane loses the first round it can be hard for them to get back into it without help. The first fight they lost bot probably meant they needed help to get back into it. That was the window for option 1. After 3+ loses in lane the lane is often too hard to recover (sometimes true after 2 loses) so go with option 2. If you can't gank the lanes in anyway then late game is the aim, focus on wave clearing so that the enemy can't easily siege your towers (so I guess 3 options), Lux is really good at that (keep using Ult to clear waves) so try your best to focus the waves and wait for farm to help the losing lane get a couple items. The problem with this is that it is a lot harder to do then the first two options because you have to keep the team alive a lot longer.
