There are many kinds of grow light on the market HPS, MH, LED, induction, plasma, you may confused on which one is the best?

First we should clear two concepts first

1. PAR (Photosynthesis Active Radiation)
As the name said, PAR by measured the effective spectrum for photosynthesis in the lamp. Some lamps with high lumen output, but the effective spectrum is less, for example lamp A :the 1000w HPS with lumen output 155000lm compare with lamp B: Philips 1000w master greenpower lamp with 139000lm, the test result showed lamp A has 9 times green light than lamp B, and the red and blue light are half of lamp B. If you want test report just leave your e-mail, I will send you.
So this is the first concept: with high PAR is good grow light. unit μmol/s/m

2. Light compensation point and Light saturation point

Light compensation point - the point for plants start photosynthesis
Light saturation point - the point for plant reach the fast rate of photosynthesis, exceed this point is no helpful to increase the photosynthesis rate.

I list some plants below:

PLANTS Light compensation point Light saturation point Photosynthesis rate at Light saturation point
(μmol/s/m,PAR ) (μmol/s/m,PAR ) (CO2μmol/s/m)

CUCUMBER 51 1421 21.3
TOMOTO 53.1 1985 24.2
PIMENTO 35 1719 19.2
EGGPLANT 51.1 1682 20.1
CAULIFLOWER 43 1095 17.3
CABBAGE 32 1324 20.3
RADISH 48 1461 24.1
CHIVES 29 1076 11.3
LETTUCE 29.5 857 17.3
SPINACH 45 889 13.2

use cucumber as example, when PAR exceed 51 μmol/s, it starts photosynthesis, so any lamps when light reach the surface of leaves still have more than 51 μmol/s, it works, reach 1421 it works better.

Of course PAR just measured effective spectrum, different plants need different spectrum in different grow stage, combo these effective spectrum as plants requirement will cause them grow best.