Is it ok for roots to be exposed to light?

I have an ebb flow system and the roots are coming out the bottom of my pots...should I cover them with more clay pebbles

Light is bad for roots. I'd fill your table with hydroton around the pots.

I agree with deadgro here I would fill in all your space with pebbles its ok to have roots coming out in aeropots as the air prunes the roots that's the whole idea of them but I wouldn't do it in ebb and flo as the roots are always wet all day due to the flood and drain, best be safe than sorry get them hidden