This is picture shows the result of a fair bit of research. What is it? 9,600 lumens of 6,500 K full-spectrum light. There is so much light from the bulbs that it looks like dusk out the window--but it is, in fact, full daylight on a sunny day. What the heck do I need all this light for? About a month or two back, my desk area inherited a bamboo plant. The window faces north and really doesn't get a lot of sunlight--especially since the blinds are usually closed. It hadn't been looking well in sometime, so I thought I'd give it some assistance. I bought a 23-watt (100-watt incandescent equivalent), placed it to shine on unhappy bamboo and let it run for about 18 hours a day. That didn't seem to do much. So rather then just guessing about plant light, I did a little reading to find out what people used for grow lights.
I knew plants needed a full-spectrum light source of some sort. But how much light they wanted was something I wasn't sure about. The obvious question was, how much sunlight would a plant get on a nice sunny day? Wikipedia has the fast answer for that on the page for the unit lux
--10,000 lux on a sunny day. Light bulbs don't use lux, they use lumens. One lumen is 1 lux over 1 squre meter. So if you had a bulb that was 1,600 lumens and mannaged to focus all the light over 1 square meter, at any point in that square meter you would have 1,600 lux. The light emitting part of light bulbs are omnidirectional, although their base of the bulb does block some light. But for the most part, bulbs throw light in every direction, so some kind of reflector is needed if you want all the light to hit a specific area. I used alumiumn foil. Not perfect, but functional.
Most compact florscent bulbs list their lumen output, and most of the full-spectrum bulbs list color temperture. But the term "full-spectrum" is used rather lossly. Pretty much all florscent bulbs emit light that coveres the entire visible spectrum. What is meant by "full-spectrum" in this context is "full daylight spectrum". Color Rendering Index (CRI) is a messure of how close a light sources comes to memicing sunlight. The scale runs 0 to 100, with 100 being 100% or perfect. My 5000 K photography bulbs have a CRI of 92. I've seen bulbs advertized as high a 98 CRI. But what CRI is needed for plant growth? One would expect that the higher the CRI, the better it would be for plant growth. But how badly does going from a CRI of 90 to 85 effect growth?
The question seemed valid, but it is a little more complicated. Plants are green, and they are green because of the compound chlorophyll. Remember that if you see a color from a non-light producting object, it's because that color was reflected. Chlorophyll does not absorbe much in the green wavelengths of light. In fact, chlorophyll absorbe highest in the red and blue portions of the spectrum. Chlorophyll is at the foundation of photosynthesis, and plants benefit most from these colors. Some people have been experementing with LED grow lights for this reason. These grow lights contain only red and blue LEDs in a ratio specific to what chlorophyll uses. Florescent light can also have modified spectrums to produce light more favrable to plants.
Knowing this, I decided to look and see what branded grow lights had for CRI and spectrum. What I found is that the majority of companys didn't even list the CRI--just color temperature and lumens. The one grow bulb I did find that listed CRI as 90, and most of the full-spectrum CFL have a CRI of 91. That being the case, I knew CRI 90 is "close enough".
So, I went ot be favorite home improvement store and bought everything I needed--bulbs, light fixtures, a cord, and a bord to mount it all to. It took about 45 minute to assemble, but soon I had a heck of a lot of light. The setup uses 6x 1,600 lumen 23-watt CFL bulbs for a total of 9,600 lumens at 138 watts. This is focused on an area of about 3 sq. ft, or about 0.3 sq meters. So the lux should be roughtly 32,000. Of course, there are some losses due to reflectors and such, but that is over the 10,000 lux goal, so we'll see what happens.