Never thought I would beat amazon in transit times lol. Lux and even par depending on the meter is not very accurate. Colored leds register higher numbers than white does. The only way to get accurate measurements is with a very expensive meter. So for us growers 24-30 may be the best starting point. My plants have a 30 inch space, others record 24 and even 20 inches. It's really about the plants reaction to the light. It's powerful