Thanks mate
No I don't measure the light. I did try an app on my phone but it would have been more useful to try and use my arse lol.
Lights on 100% as my first cobs weren't dimmable. I've just made another 250w set and this is dimmable. It's on 100% though lol.
Controversially, I start my cobs at around 36 to 40 inches (90 to 100cm) above the seedlings and don't move them at all. I just let the plants grow up to whatever height they fancy. Seems to work ok so far.
I think you do have to be careful as cob light is so intense. Too close at too young an age and they will show stress and possibly stunt worse case scenario. Same as blurple led i guess. I definitely think when they are young is the critical time with cobs. Get them higher than you think they should be, and then move them up a little bit more! When the plants are big they can take a lot more intensity.