Hi there
For a 150 watt from seedlings i would be dimmed at 50% and around 50cm above for the first week or two you dont want to be too intense/hot and damage the first two leaves,
I would put it up to 60% week after and 80% week after that..
Keep an eye on them.. if the leafs look like they’re drying up they probably getting too hot, if they start stretching like crazy and there getting a really long stem then lower thr light abit,
Its all about trying it and monitoring it and your start seeing what they want,
Best of luck 🌱