Baby Plants Leaves are turning yellow green? to much heat?

got a 600w mh and set it up above my seedlings about a week old temp was not too hot and distance from plants was about 2 feet, it was warm to the top of my hand but thats it did i heat stress the plants? now the ballast is running at 50% and temp is much lower in the room

How old are your plants. Are you feeding them anything. What kind of soil?

Way too young for 600w at 2' away. Keep it at 50% and transplant those seedlings into bigger pots real soon, like today.