Simple math, and it doesn't need to be any more complicated than that for basic comparisons.
With emphasis on 'basic'. And in a fictional situation where nothing else than par/w eff of the light source matters. For a more realistic comparisson however it's not that simple and more to it then running cobs soft to reduce power usage and increase par/w efficiency.
@Abiqua, open your mouth:
"Light affects the characteristics of plant growth and development at virtually every stage of the plant life cycle and influences both morphogenic features and intracellular metabolism. In many cases, the physiological responses triggered by photoperception are mediated by changes in gene expression and are accomplished by the coordinate activation or suppression of specific batteries of light-regulated genes (Tobin and Silverthorne, 1985;Gilmartin et al., 1990).
Light has been shown to activate the expression of gene families that encode proteins involved in photosynthesis, nitrogen metabolism, and flavonoid biosynthesis. [mere examples] "
Read:
https://books.google.nl/books?id=q2bvAgAAQBAJ&pg=PA669&lpg=PA669
E.g. "Light quality is an important factor for essential oil production."
"However, isoprenoid production is induced by UV radiation, but not always supplementary UV-B leads to increased isoprenoid production (Dolzhenko et al. 2010). Maffei and Scannerini (2000) reported ..."
Read about isoprenoid, mep pathway (from which cannabinoids are derived as well), combine with keywords like oils, or specific terpenes.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740396/
Cannabis Sativa, plant of thousand and one molecules
And not just terpenes as has been known for a while... see:
EFFECT OF LIGHT QUALITY ON CANNABINOID CONTENT OF CANNABIS SATIVA L. (CANNABACEAE)
Or:
"Various studies have indicated the positive effect of cytokinin on terpene production." cytokinin "regulates gene expression". "Cytokinin takes part in light response modulation and affects the circadian rhythm regulation and phytochrome functions (Chen et al. 2006, Naito et al. 2007, Yakir et al. 2007)."
"Environmental conditions can influence essential oil biosynthesis, since it may alter hormonal balance. Thus, phytohormones may act as signals that can, directly or indirectly, induce secondary metabolites biosynthesis (Prins et al. 2010). Light availability and quality can be positively associated with essential oil production, as observed with
Cymbopogon flexuosus, which showed an increase of approximately 30% in essential oil biosynthesis when plants were treated with red light (Sangwan et al. 2001). "
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2197-00252013000200008
"UV-B modulates the interplay between terpenoids and flavonoidsin peppermint"
Modulation of secondary metabolites by UV-B involves changes in gene expression.
http://www.academia.edu/1175424/UV-B_modulates_the_interplay_between_terpenoids_and_flavonoids_in_peppermint_Mentha_x_piperita_L._
Just examples of the huge amount of research available that shows how much the expression of the relevant genes are affected by the "quantity and quality" (that was a quote already...) of light. There is a lot more fruitful potential there than just beating hps in terms of par watt efficiency.
