HelpfulGardener.com

My Ficus, Serissa, and Jades live under lights that are on 12 hours a day [Timers are cheap ] when not outside in the suitable seasons.

IMO LED are far too expensive.

Metal Halide & High Intensity Discharge, High Pressure Sodium both also have this issue [For the average hobbyist- IMO] as well as being inefficient wrt energy and much of this energy is wasted as heat. [I have heard that the HID systems are getting more energy efficient recently.]

Heat is a major issue by itself as incandescent bulbs often need to be a 12" to 16" or farther away from the trees and MH HID, & HPS often require their own ballast as well as additional ventilation to dissipate the extra heat they generate.

I use A pair of 4' shop lights w/ fluorescent full spectrum bulbs, [27 watts, A color temperature of 6000 and they put out about 10 to 12,000 lumens as I recall] On occasion this has been supplemented in spots with a few of those spiral shaped fluorescent bulbs situated in clamp lamps.

It is important to know the distinction between 'watts' and 'lumens' when you are shopping for plant lighting, As buying a 'higher wattage' bulb may simply be increasing your electric bill and benefiting your trees only marginally.

A 'Watt' is a measurement that refers to the amount energy the bulb consumes.
IE: Your power bill is measured in kilowatts [kw=1000 watts]

A lumen can essentially be defined as a measure of the amount of visible light emitted [Or available at the point of measure.]

Do always look at the packaging, It is a relevant thing to know .

More lumens the better! Look for something in the 5000 to 5500K color temperature range for balanced growth, [It is on the package. 3000K is for blooms- 6500 is more green foliage oriented...All will work]

I am glad to see your shopping for a fluorescent bulb [With an eye on the lumens no less! Remember that the 'watts' re: to the power consumption-Not the brightness. ]

You can get that bulb [or similar] and an [Admittedly ugly] reflector for less than 15$. Or go whole hog and get 4' shop lights for under 40$.....

Light intensity reduces massively over a very short distance.
The technical geek way to put it is generally: The reduction in light intensity is equal to the square of the distance.

Which simply means that if you have a tree 1' away from the equivalent of 1000 lumens and then you double the distance to 2' you now have only the equivalent of 250 lumens. this number drops even more dramatically as the distance grows. 6' of distance and less than 28 lumens reach the tree. I know this is a bit off your original post but It's frustrating to hear people who put their indoor tree 5' away from the window for fear of the :shudder: direct sun when most likely it is the lack of humidity that is slowing it down [And it could really use the sunlight too. I accept there may be temperature issues with some species.]