Rough lux lighting levels
There are several different 'ideal' levels of light intensity, depending on the stage of growth your plant is in. The following information is useful when figuring out how much 'headroom' you need, or distance between your light source and the canopy of your plant (many people use 'bucket spacers' to gain distance). Lux meters in general should only be used for white light, not mixed/monochromatic light sources (for example, 660nm red LED, 440nm blue LED). Be sure to always measure from the top of the canopy.
These measurements correspond to a white light LED CRI 80 (in this case 70 lux is equal to 1 µmol/m2/sec):
- 5,000 lux = unrooted cuttings (you don't want too much light)
- 15,000 lux = lower end for seedlings (common microgreen level)
- 25,000 lux = lower end for vegetative growth
- 40,000 lux = lower end for flowering
- 75,000 lux = this starts to hit light saturation
These values is only valid for white light. Except for unrooted cuttings, you want to stay above these numbers. I've grown seedlings fine at 35klx, and many people on the /r/SpaceBuckets subreddit are running their plants at >75klk or equivalent. You really want to stay above 40klx for flowering, and many professionals are going to be closer to 75-90klx. I tend to grow plants at higher lighting levels myself. As a general rule, if your seedlings are 'stretching' then you need more total light or a higher color temperature light.