Roots and light

So I had a abundance of 5 gal clear plastic water jugs, I cut the top off and use this to transplant in. It didn't take long after transplanting for the roots to be seen spreading thought the soil mass. I've never had any adverse reaction from the roots being exposed to light, but I've read on somewhere that it's not good for something. Like I said never saw an adverse reaction here? whats suppose to happen?

they die, but you can simply put tape on your jugs to block out the lite

the roots can grow exposed to light, but their growth will be much slower than if in the dark. Not saying what your doing wont work, but your grow will go much better if they are in total darkness. Light tighting my cloning tub made my clones root a week faster for comparison.

well, I'll cover them, but I don't know if theyve caused harm yet, im bout 4 weeks in flowering and they been hurt at all.
There's a lot of folk lore and does and don't when it comes to weed, I just wonder where some of it comes from.