you should write every horticultural light bulb company and tell them there all wrong to put the lumens out-put of there bulbs on the side of there box.
"Plants use light energy between 400 and 700 nanometers, the region known as Photosynthetically Active Radiation or PAR.
Illumination for plants, also known as "irradiance", is sometimes measured in PAR watts per square meter (W/m2). Another means of measuring light quantity for plant growth involves discrete units of quantum flux in the PAR region called "photons". Photon flux is commonly measured in units of micromoles per square meter per second (µmoles/m2/s), where 1 mole of photons = 6.022 x 1023 photons.
This is an objective measure since it directly indicates how much light energy is available for plants to use in photosynthesis. However, lamp manufacturers typically rate their lamps in lumens, a measure of light in the spectrum visible to humans. Moreover, most lighting engineers measure lighting levels in lumens per square meter (lux) or per square foot (foot-candles). Since the spectral sensitivities of plants and humans are quite different, there is no direct method of converting the units without evaluating the full range of spectral characteristics for a given light source."
