When the bucket is full of media like hydroton or gravel, no light will penetrate past the first inch. Try to shine a light through it. if it shows up on the other side, it might grow algae. The roots would be unaffected, but it would be a waste of nutrients and also cause the pH to fluctuate. The white ones I've seen would work. If you're in doubt, you could also cover them with foil. That's a cheap fix.