m0useanswered grow question 2 years ago Reference the official page
https://acinfinity.com/hydroponics-growers/led-light-boards/ionboard-s33-full-spectrum-led-grow-light-240w-samsung-lm301b-3x3-ft-coverage/#product-warranty
Find the Manuel
https://acinfinity.com/content/IG2108X1_210813_IONBOARD%20Manual.pdf
Page 12 hang heights.
Take it with a grain of salt the specs are almost always inflated and lights can go closer most times.
I would start off at 25" and try moving it closer till you notice stress. Can calculate your DLI and that's a better option but you need a functioning light meter.
Light meters on phones work but they are not accurate. To make it work accurately you need to calibrate it. once calibrated it is great. That being said they will be always the same level of inaccuracy uncalibrated so can use whatever number it is giving on the device as a standard just know its not true. Use the same device for new readings, not another phone even if its the same model.
Good Luck!