How soon to expose seedling to light?

I finally got a seed to pop and start a decent tap root, close to 1/4" now. I got the system set up and transplanted the seed into the sponge, sealed with label/protective top, and put it in the system with humidity dome on top. Of course I covered the other holes.

I have two sets of questions:

1) What is the best direction to put the seed in, tap root up or down? I have seen som nay say down, but it seems that those who has studied how plants naturally grow say that you place with tap root up so it will curl down naturally and conserve energy.

2) If tap root is up, won't that expose to light which is bad? Or is it ok when the tap root has gotten to be at least 1/4"? Are you supposed to keep a dark cover on top of the seedling as it starts in the Aerogarden until the stem starts to break out of the sponge, or do like I have seen so many on videos do and run the lights from the very beginning with just the clear humidity dome?

Tap root down. The plant will figure it out but why not just put it downward to begin with.
No you don't want to expose the root to light. You need something to protect the roots from light that is why you use a medium or light barrier of some kind. The only thing you want to hit light is the leaves. The stem and leaves can receive light from the moment they sprout.

trichromalicious said:

Tap root down. The plant will figure it out but why not just put it downward to begin with.
No you don't want to expose the root to light. You need something to protect the roots from light that is why you use a medium or light barrier of some kind. The only thing you want to hit light is the leaves. The stem and leaves can receive light from the moment they sprout.

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So I should definitely cover the pod with a dark dome and just run the Aerogarden with no lights on, or with the lights on to create some warmth? Or is the paper pod cover considered enough of a light barrier so that you can run the lights with just the clear humidity dome on top and no dark cover?

I have looked at several videos online and I never see anyone mention using a dark cover until the seedling spouts out of the sponge and produces leaves, but it seems logical to me. Even in the Aerogarden guides I have seen for growing MJ, they never mention keeping things in the dark except for when you are trying to get seeds to crack... they just say plant the seeds in sponge, place in the Aerogarden, and turn the lights on 18/6 or 24 hours from jump.