Distance from lamp to bush

Personally - I spent the .99 usd on the Photone app (Android and iphone) - had to pay to unlock led measurements but it hasn’t failed me in past 6 months. If it’s iPhone - ya use printer paper as a diffuser. I aim for 300ppfd weeks 3-4. 400ppfd going into 5. I do slow increase on the dimmer to reduce stress but keep the light 12-18 inches away from top of plant. That just me though 🙂

1882bean got the right idea use the app and just remember the light will throw heat too so consider that as well

App called " tent buddy " or " photone " has helped me get my ppfd numbers and dli numbers in check. That way ur not adjusting blindly . Best of luck.

With a QB (quantum board) i'd stick to 18-24" primarily to even out blanket of coveage and reduce hotspot in center. trial and error to tune it in to you context... a fre lux meter app can help recognize propotional intensity... i.e. how much lower on edges compared to middle? 50%? 75%? it will be stronge in center, no matter what, and i'm not saying what is optimal, as that would take some measurements and math to figure out what povides most with least loss to absorption while still getting good growth along edges and not sacrificing more in teh middle than what you gain... lol.. it's complicated... have fun with it.