I was "out sick" for several days.
My take is that T12 bulbs are obsolete but still cheaper than T8s. T8s are cheaper to buy than T-5s, and much cheaper to run than T-12s.\
Maybe LED lights will replace all florescent tubes sometime in the future, but I'm going to wait for LED fixtures to keep dropping in price before I buy any.
Both T8 and T12 use new technology similar to "Compact Fluorescent Lights" (CFL), so they are much more efficient than the old-style T-12 bulbs. They also use a different ballast than T-12 fixtures used to use.
In addition, T-8 and T-5 bulbs can be made brighter than T-12s, and that seems to me like a great big thing for growing seedlings. Giving them "plenty" of light seems better than noodging T-12 lights up an inch at a time, trying to keep them super-close to the seedlings to make them effectively brighter.
I know that lots of very experienced people grow many seedlings with nothing brighter than T-12s, but my small setup would be greatly improved by something brighter (and some carpentry to hang them from).
Other T-5 bulbs and some T-8 bulbs were designed not for extra brightness, but for long-life or extra-extra efficiency. You have to read the details if you buy a box of T-5 or T-8 bulbs, and decide whether you want to pay extra for even more brightness or even more efficiency, or pay less up front for the bulbs, or get bulbs that won;t need to be replaced as often.
My "color" advice for starting vegetable seedlings and common flower seedlings is traditional: "one warm bulb and one cool bulb".
Ken, I hope you do correct me, and/or extend these comments into the land of orchid-growing, because I have a caveman approach to lighting seedlings. "Brighter is better." "More photons!" (Maybe African Violets are fussier than seedlings.)
"Some blue spectrum and some red spectrum" gives the plants everything they need for basic growth. Fluorescent lights are never going to give a continuous emission spectrum like the Sun, they only emit "lines" - light at specific frequencies - determined by the particular phosphors they are coated with.
"Broad spectrum" tubes have a tri-phosphor coating that spreads out those "lines" somewhat, but chlorophyll doesn't actually need that. You can grow many plants successfully under sodium lights that emit just one or two sharp lines (as long as they get enough red for proper elongation and enough blue for whatever - blooming?).
Some sources claim that "Grow Lights" are nothing more than "broad spectrum" (tri-phosphor) tubes with a fancy name stenciled on, and a much higher price. They also don't last as long as regular tubes, and are less right. "Give me more photons" - generic photons - for my seedlings, and fancy color spectra for portrait photography!
Ken?
