The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the
luminosity function.
http://en.wikipedia.org/wiki/Lumen_%28unit%29
Spectral Requirements for Flower Initiation in Two Longday Plants, Rape (Brassica campestris cv. Ceres), and Spring Wheat (Triticum×aestivum)
Action spectra for the promotion of flowering by long periods of irradiation in the red and far-red regions of the spectrum have been determined by the use of interference filters. The percentage floral initiation was greatest at 710–720 um for both wheat and rape (about 1 k erg · cm−2· s−1).
Lowering the temperature from 35 to 15°C did not shift the most effective wavelength, suggesting that the effect of high levels of radiation at 710 nm was not related to a balance between photoactivation of phytochrome and its destruction. In both wheat and rape, an increase in temperature promoted the flower-initiating action of broad-band far-red and 710 nm radiation more than the action of broadband red or 660 nm radiation. The flower-promoting effect of broad-band red and 600 nm radiation was particularly depressed by temperatures above 25°C.
It is concluded that the promotion of flowering by long periods of high energy at 710 nm is caused by the activity of a high-energy pigment, rather than through a special effect of phytochrome.
http://onlinelibrary.wiley.com/doi/10.1111/j.1399-3054.1968.tb07348.x/abstract
UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES
Abstract
The effects of UV-B radiation on photosynthesis, growth and cannabinoid production of two greenhouse-grown
C. sativa chemotypes (drug and fiber) were assessed. Terminal meristems of vegetative and reproductive tissues were irradiated for 40 days at a daily dose of 0, 6.7 or 13.4 kJ m-2 biologically effective UV-B radiation. Infrared gas analysis was used to measure the physiological response of mature leaves, whereas gas-liquid chromatography was used to determine the concentration of cannabinoids in leaf and floral tissue.
There were no significant physiological or morphological differences among UV-B treatments in either drug- or fiber-type plants. The concentration of Δ9-tetrahydrocannabinol (Δ9-THC), but not of other cannabinoids, in both leaf and floral tissues increased with UV-B dose in drug-type plants. None of the cannabinoids in fiber-type plants were affected by UV-B radiation.
The increased levels of Δ9-THC in leaves after irradiation may account for the physiological and morphological tolerance to UV-B radiation in the drug-type plants. However, fiber plants showed no comparable change in the level of cannabidiol (a cannabinoid with UV-B absorptive characteristics similar to Δ9 THC). Thus the contribution of cannabinoids as selective UV-B filters in
C. sativa is equivocal.
http://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.1987.tb04757.x/abstract