MAXIBRIGHT LED

I'll apologize up front because you are going to hate this response. It's not a simple answer to ask "how high" since it also depends on the size of your tent or how much area you want to cover. Your light could deliver enough light on low power for a plant in the center spaced 6" high. But, that leaves the corners of your tent very dark. So, you raise the light for better dispersion which drops it's intensity so you need to crank the light up to higher power. But how high do you turn the dial on the light. Most light power knobs are not calibrated or linear. The 1/2 position on the dial may not be 1/2 power for the light. For many lights zero on the dial may actually be 15-50% power and half dial could actually be 75% power. Instead of just saying how high it's much more accurate to measure the light instead of just going by distance and a guess on your light's power dial. I measure the amount of light at the top of the plant and set the height or power based on the DLI chart (daily light integral) and how much light the plant needs in each stage of growth. A PPFD meter would be best but they are expensive. I use a app on my phone to measure lux. My light manufacturer provided a conversion factor to convert lux to PPFD (for my light 1 PPFD equals 65 lux). Then with that information I can set the height and power of my lights. For example. Nearing the end of flower you might want a DLI of 35 in 18 hours. Using the chart you can find that 35DLI in 12 hours needs a light intensity of about 500 PPFD. My light's conversion factor is 65 so 500 PPFD x my 65 conversion factor I end up with 32'500 lux. I hold my phone at the top of the plant and move the light up or down or vary it's output until I'm reading about 32'500 lux. With my light on a lower power level might produce that light intensity 12" above the top of the plant but being so close the light doesn't spread out far enough to provide good light in the corners of the tent. So, I raise the light higher to better spread the light across my whole tent then I adjust the power as needed until I get 32'500 on my phone. And always pay attention to what your plant is telling you. If it is stretching then it probably needs more light. If you see signs of light burn on the top parts of the plant you need to raise the light or back off on the power knob.