Cactus / asterias seedlings

I removed a cover made by 50 % shade-cloth, covered over 2 years old A. asterias seedlings yesterday.
Since the daylight hours have been shorter, I try to give more sunlight onto seedlings.
The photo is one of seedling pads, accommodated my seedling No. 8, 9 and 48.
Each of them is in a 50 mm square tube.
All seedlings were cut their tap-roots last August and rooted again.