because, just as i learned from the 80s when i literally re-read jorge cervantes' indoor marijuana horticulture a dozen times, halides promote full terpene expression by simulating daylight, while limited wavelength sodium mostly simulates warm summer sunsets that trigger flower, and only allows the chemical processes in the plant that use that particular spectrum with green being the most useless spectrum. that's why my very first lamp was a halide.
bottom line... halides for quality, sodiums for quantity
when someone yet again implied i was full of shit and/or lying about the terpenes i expererience from LSD, C99, and especially super cali haze, i had to look the explanation up, at first getting a link or two about terpene expression under full spectrum in general, then remembered DJ shorts talking about it too in his article here:
https://www.rollitup.org/breeders-paradise/48788-tips-breeding-dj-short.html
where he suggests halides especially for landrace sativas. it's also why there's a metal haze by whoever bred that and named it after the halides he grows under. i don't have the link to the info, but if you keyword spectrum and terpene expression, you should be able to fiind the info easily if you still need further proof.
then there's utraviolet which many growers are so afraid of that they refuse to use it, even with tanning bulbs, but studies have shown that it helps improve THC production. halides might not produce UV as that's filtered in the glass if there is any for safetly, but the fuller spectrum definitely gets closer to it than red/orange sodiums whose spectrum probably overlaps into the infrared more too and heat destroys THC. i seem to remember recently reading that sodiums do p[ut out more heat and need more spacing than halides. that could just be a factor of their higher lumen output per watt though. all i know is after reading up on he subject, i always called sodiums stoner lights in my head. they're all about quantity over quality. i'm surprised no one even runs both light types much anymore as that was considered best in the 80s, and often the ratio of 2 sodiums to one halide has been given, but i'd go the other way myself.
there's a graph somewhere online that lists the exact spectrums plants need for certain processes with one, around 420nm (or less, red) and another in the blue spectrum, maybe 700 something nm. red isn't the only spectrum plants need, and they don't do much with green, yellow or orange i think.
it's just like with most people. you get vitamin D from sunlight, and when winter grey skies come around, a lot of people get seasonal affective disorder. plants are happier with natural light. sodiums are the equivalent of sweatshop bulbs.
this link looks familiar, i think it was the first reference i found trying to prove WHY my LSD & super cali haze had fruity grape phenos, less so in LSD, but that also expressed just a bit of haze catpiss pheno in early flowering that faded that REALLY pissed someone off that i reported that.
that's what cervantes knew at least by 1985, as well as predicting SCROG when everyone was still growing 3 foot sea of green plants in 3 liter soda bottles. i can't find the more technical description of terpene expression. it was at some general gardening website i think, and in looking it up again, the heat issue came up regarding terpenes on an ICmag thread, but i'm pretty sure it has more to do with specific spectrums for specific processes with red definitely being needed for flowering, and blue helping vegetative growth.
i thought a lot of my different strains had a pretty similar fruity flavor under sodium. if both my C99s and ESPECIALLY super cali haze had a more specific grape flavors under halide, i expected their offspring to have at least some of that same flavor, but it was as generic and fruity under sodium as several other jacks, thais and hazes.
so far, my personal experience agrees with what uncle jorge taught me. i don't like red in general anyways, and i don't like working under that color either, but that's just a personal preference.
i really miss my copy of indoor marijuana horticulture. it had 3x the info of my other two guides combined that maybe added a couple dozen tips cervantes missed between them to justify their existence. i really should get his most recent edition and re-read it a few times, but i'll still keep skipping the college level genetics chapter like the even deeper info in the copy marijuana botany i still have.