Candle but if you are like me all you can tell is that they are dark or clear....
I would wait one more day then open a dark one.
Wow, you are like me. If they glow, then nothing is going on, but if you can't tell what is going on, then you are probably good to go.
To the OP: Is it 19 or 20 days? I would personally wait until day 21+ to scrap for recycle.
Mine usually hatch 18 days +/- 6 hours from the time I set them. Never had a 17 day hatch...yet. 19 days is a bit long but within range.