At day 18/19 you should go into lockdown and that's when you need to up the humidity. Then it really needs to be at least 65% for the rest of the hatch, I recommend more. Yes, a flashlight should work well enough to let you see the air cell. There are a couple threads on here as well on making your own candling devices and what other's have done.
One thing you could consider is running a room humidifier in the room in the vicinity of the bator. If the room has a little more moisture the bator might hold it a little better. There are a ton of them now that don't even look like humidifiers and add to room decore.
How far into the hatch are you?
Exactly right about the high humidity. I now aim for 80% and it often spikes to 99%. As a result, my "shrink wrapped" chick problems are no more.