Lux numbers? Maybe?

figure ambient co2 caps out at 35-40dli... so your 'max' bar is somewhere 850-900ish? give or take a bit more prolly. i don't have a dli table in front of me... it's worth a read though.

lux values will vary by equipment not related to actual number of photons applied to the plant, which is the number that matters. that's okay.. knowing the exact 'ppfd' of what you provide is useful, it isn't required to find an upper threshold for your plant. You can get a good guesstimate from specifications of the light, if accurate... How far from canopy is more about distribution of diodes when limited to midrange and high-end equipment. quantum boards should probably be 18-24" -- trial and error based on behaviour of plant over time... (hours of use key too) or something more spread out, lik ethe 'spider' framed lights with bars you can do 12-18" depending on intensity .. and hours of use. e.g. if relying on ambient co2, and running 12 hours per day, it may reuire ~12" from canopy to push the maximum 'DLI' for your garden's variables. (daily light integral.. google that and should find good resoureces to explain all the terminolgy) Lux meter can still be very useful in this process. It does a good job reporting proporitonal intensity, but it'll be somewhat equipment-specific values due to varying sfd of any light. that's the advantage of using par.. it's apples to apples regardless of equipment used. but if you find under 1 specific model of light that 18" and 12/12 is just backed off from causing lgiht damage or excessive drooping etc, you know that particular lux value at canopy with that light will be at or near the maximum for most plants... with genetic variance possible and varying availability of co2 etc. when you try to dim light and give a certain proportion of that 'max' for some seedlings or clones, you can be confident about those calculations using lux, relative to the value you find as described in above example. 25% of 'max' lux will be 25% of 'max' par too. (the quotes denote that the max varies based on relevenat local variables)

LUX is a measure of the intensity of visible light, and means very little for plants. You want to look into photosynthetic photon flux density (ppfd, measured in micromoles per meter squared per second), which takes the PAR (photosynthetic active radition) distribution into account. This is what matters to plants. Good luck!