RickCorey's blog: Fluorescent Bulb Types

Fluorescent Bulb Types   Standard old T-12 fluorescent bulbs like shop lights emit 2 ½ time s as much light per watt as incandescent bulbs.   It's true: incandescent bulbs  are less than half as efficient as old fluorescent bulbs.  Use incandescent bulbs for heat.  Use fluorescents for light!  The newer style are much more efficient than old T-12 fluorescents. When they have screw-in bases and built-in ballasts, and usually have "pretzel-twist" tubes, they are called "CFL" for Compact Fluorescent Bulbs. T-5 and T-8 tubes have similar new technology, but I guess are not usually called "CFL".    - T-12 bulbs are 1930s technology.  T-12s are dimmer and much less efficient than modern CFL bulbs (or T-8s or T-5s).  - T-8 bulbs (early CFL-like technology) are much more efficient than T-12s and a little brighter. Their price is now dropping to match T-12s.  - T-5 bulbs (newer technology) can be twice as bright as T-8s and about as efficient.  T-5s are more expensive per tube, but around the same price per lumen.    - Old-fashioned 4-foot T-12 tubes consume 32 or 40 Watts of electricity and they only emit 2,100 to 2,800 lumens. They are the least efficient and least bright type of fluorescent bulbs.   (There are newer, higher-rated T-12 bulbs that go up to 3,200 lumens, but they are more expensive and less efficient.)   You shouldn't use the new T-5 tubes in old fixtures because they need different ballasts (electronic ballasts) and T-12s need magnetic ballasts.  Some websites and books say that you CAN run T-8s in a T-12 fixture "since the pins fit", but it's bad for the bulbs and inefficient.     - T-8 bulbs use only 28 - 32 Watts of electricity.  T-8s are  much more efficient and somewhat brighter than T12s.  I see light outputs of 2,725  to  3,000  lumens.  It looks to me as if the newer T-8 tubes are coming down  in price to equal the T12 bulbs.    - Some T-5 tubes are almost twice as bright as T-8s - they use 54 Watts but put out 5,000 lumens.  This is a cure for spindly, leggy seedlings!  There are "High Output" T-5s and "High Efficiency" T5s, and others with unusually long lifetimes.  Special features cost more.  T-5s are still evolving and falling in price.  Some T-5 bulbs cost up to twice as much as T-8 bulbs, but they do emit twice as much light.  It may be worth paying the shipping if you find a good price online for a case of T-5s with just the features you want.   Color, Spectrum or "Temperature"  Pretty much any type of tube can be found in any color "temperature" (any spectrum) - cool blue, warm red, white or daylight.  Light that is too reddish sometimes causes elongation.  But don't spend money on "spectrum" at the expense of brightness.  Brightness (intensity) is more important, and it comes from lumens, plus closeness to the plants, plus good, clean reflectors.   I plan to continue using one cool blue and one warm red tube to cover both ends of the spectrum at least cost, greatest efficiency, and better bulb lifetime.     Broad spectrum "grow-tubes" (tri-phosphor coatings) are a little different from color.  Broad spectrum tubes have tri-phosphor coatings to "spread out" narrow spectral peaks.  They have a more uniform distribution of intensity all across the spectrum, instead of sharp peaks and low valleys.   I've read that really expensive grow-tubes are just moderately expensive "broad spectrum" tubes that were re-labeled with marketing claims.  Both broad spectrum and grow-tubes are less efficient, more expensive, and don't last as long as regular tubes.    It's debatable whether broad spectrum tubes do any better for seedlings at all.  I believe that chlorophyll absorbs it all and turns it all into energy (except for the narrow green band that makes plants look green).  But there may be seedling subtleties that I'm unaware of.    http://en.wikipedia.org/wiki/Fluorescent_lamp#Color_temperature   Tube Lifetime   Any fluorescent tube becomes less efficient as it ages, and less bright.  The rule of thumb with T-12s used to be "replace every 2 years if used 18 hours per day".  "20,000 hours" is claimed, but at the older age,  they give dimmer light and wast more electricity.  You should replace bulbs before they develop black spots, or flicker, or fail!    If you put new bulbs into one fixture and you can tell by eye that it's significantly brighter than another fixture with old bulbs of the same "color", it is time to replace the old bulbs.    Even if some intense but old T-5 bulbs are still bright enough to keep seedlings happy, at some point the saved electricity will pay for new bulbs.  At some later point, the saved electricity will pay for the cost of new bulbs PLUS the resources consumed to produce and recycle them.   How to get more brightness without replacing bulbs?  Clean the tubes and reflectors!  Move them closer to the plants more often.  Hang more reflectors down the sides and ends of your trays (but keep good air circulation).     Mercury   Modern CFL bulbs have only around 3 milligrams of mercury per 4 foot tube.  That's less mercury than would have been released from burning enough coal to power incandescent bulbs!  But it is still mercury, which is very toxic.    Many states don't consider 3 mg enough to call it "toxic waste", but YMMV.   There are eco-friendly CFL bulbs with 1/3^rd the mercury (1 mg per bulb). I assume there is some trade-off in brightness, efficiency or longevity.  T-5s are still being improved, so read the fine print and watch for new models.   - - T12, T8 and T5 stand for the diameter of the tube in eights of an inch. T12 are 1 ½" in diameter.  Twelve eights of an inch add up to 1.5 inchs . T8 bulbs are 1 inch in diameter. Narrow, bright T5 tubes are only 5/8 inch in diameter.     http://www.littlegreenhouse.com/accessory/lights2.shtml

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