Seedling Height? See diary entries for a better idea.

Yes, she's stretched a good bit. Take that box off. Your RH is to low. Throw up a wet towel and leave the doors closed If you've a tent you can raise the RH and temp by timing the exhaust the air every 10-10 and it'll raise your Rh. Or ever 5 on and 5 off whichever suits your timer. Light should be at. 45cm from leafs. 35-40% for now and turn up. You shouldn't need to go beyond 50-60% for your entire veg. Or you can do what I did. Twist the stem and pin it now. Making it lower to your pot when you've taken it out of the gas chamber. Hard to fit a wet towel under there. But you could put some hot water from a kettle in a little cap it'll quickly raise the RH for hours. But as you are doing hydros you can put it at the end of your net pot and cover it in with clay pebbles or whatever you plan to use just be careful if you plan to transplant into water soon. Good growing

I agree with growstick but also need to adjust your RH is very low for a little sapling and needs to be in the high 70's and temp should be up a ways to in the 27c or so..