My very first grow ever I had the lights at 30” and “partially” turned down...I stunted the hell out of them...Newbie learning led to me buying a Lux Meter (DrMeter on Amazon) so I know what I’m blasting them with. HLG put out in a blog post that their lights tested out to allow a PAR to Lux conversion of 0.015 (so if you find a chart indicating a desired PAR of 500, you convert to Lux by dividing by 0.015 giving a Lux of 33,333). This conversion has been really helpful so my $40 lux meter could work, instead of having to spend $$ for PAR meter.
I started my (current grow) seedlings under a lux of 3500, and slowly increased. I’m still in my “first” grow, having had to restart after my burned seedlings, so I am still testing out what my plants respond to. I am in flower now and still haven’t turned it up to 100%. I am keeping my DLI around 40 right now and monitoring how the plants respond. The plants seem to be doing really well.
I got mine through LEDgrowlightdepot and have been really happy with their service. I had a bad dimmer on one light and they handled the warranty through HLG for me - I had a tracking number for my replacement light within an hour of me reaching out about the issue. HLG has since stopped using that kind of dimmer and now ships with the new one (I know this because I might be addicted to this hobby and have already expanded my grow setup to multiple lights/tents!). I have no affiliation with HLG or the light seller, btw. The light depot has reviews that give par readings and suggested grow heights, too (since that is what you asked me for!).
I hope this helps. You’ll love the light.