The just do it.

Not a simple answer. As always you need to learn more about stuff you are using to achieve your goal.

Actually it wrong terminology. Probably you need to provide different illumination delivered to the plants.

(A) you can use the same LED intensity (Power) setting but need to change the distance from plant. Need to use illumination meter to record illumination.

(B) you can use the same distance bu change LED Intensity (power - driving current). Also you need illumination meter to calibrate set-up.

Good luck,

Branko