I understand lumens PAR etc., that isn't my question. My question is why does light from an HID lamp (be it MH or HPS) travel further (therefore penetrating better) than CFL light of equivalent wattage? Or if you guys prefer why do HID's penetrate better than CFL even if lumens or par ratings are equal? To be clear i'm not arguing for or against using either, i am simplily curious as to how the mechanics of the bulbs differ to produce greater penetration.
For the record lumens are terrible way to measure a bulbs worth for growing plants.
I believe it mostly has to do with an HID bulb being closer to a point source, as compared to a CFL which spreads the light source out over a larger area. Two identical lights putting out the same amount of light energy, the one with the smaller surface area will have better penetration because of less spread. Inverse square law explains this.
HID putting out more light (lumens or PAR or whatever) per input watt than CFL explains why they are more efficient. Or brighter. Not why they have better penetration.