Vapor - I would think they wouldn't grow as tall as you want. I can't say that them being uncovered would truly stunt their growth, never have done it without the lid. Mine so far, as you can see from the pictures, are doing wonderfully covered up. I love how the roots are so clean and so is the water with the Advanced Nutrients. So here are some pictures for you I took when the lights came on. I actually quit using any medium at all. I stuck my clones inside the 3.75 inch neoprene insert and then stuck the insert inside the net pot. The plants will never get over 5 feet tall in my application and the root ball inside the cup supports the plant itself. Now I don't have to deal with dust and debris.
This one shows the PVC and sprayers inside the tray. The roots are obviously hanging down from their netpots suspended in air by the tray cover.
This one shows the red shutoff valve I use. I am going to grow 4 strains, 9 plants each and want the ability to water each section if one is empty, so I attached this valve. It's a 1/2' ball valve. Nothing special
Here is the tray, the plants, and the small 10 gal reservoir under the table. Water just drips back into the reservoir once the timer turns off.
10 gallon reservoir. The rubber brand. I love this brand because the lids seal well. You can see the salt build up on that lid from the other nute package I was using.
And finally, this is a picture inside the reservoir. No, it is not brown algae or anything. Just the reflection of the light. The water itself is actually very clear. I keep the water level just above the pump. Notice it laying on its side. It still sucks water just fine, I can just let the water level get a little lower.
Hope this helps some! Sorry to take over your thread Vapor!!