I have a Mars hydro 300w which is true 140 watt...I have it on one plant how far should I keep from canopy
LEDs tend to burn hot when you first put your plants under them. Hang it at a distance you are sure is too high and then lower it over the coming days until it reaches a point where your plant is responding well to it. Of course, you don't want to hang it too high to start with or your plant will stretch on you. I think safely you could go 18" to 24" to start with and then lower it on down. They love LED light once they have a chance to adapt to it.
the manufacturers website usually has the recommended distance from top of your plants the mars II 1200 is 30 to 24 inches so.
With a MarsHydro 300w you will want at least 18" from the light to the top of the plant. Any closer and you will see light stress on the top of the plant. Also plants unders MarsHydro 300's NEED a lot of added Cal/Mag or you WILL get calcium deficiency.
Seedling 24-30 inches Veg 18-24 Flower 12-18 inches Sent from my iPad using Grasscity Forum mobile app