1. Should work for cuttings and seeds. However, in summer in a sunny window your lights are probably blocking more light than they provide! I'll answer the rest of the questions assuming the lights are used without sun, since the lights are pretty much a waste of time if you have direct sunlight.
2. CRI is a measure of how close the spectrum is to a continuous natural daylight spectrum. 70 is in the "not very" category, but don't worry, your plants will still grow roots and your seeds will still sprout.
3. Cool white has a less orange-ish and more blue-ish appearance. 3000K is warm white. Cool white is 4100K or thereabouts. "Daylight" fluorescents are also fairly easy to find now at about 6500K. Using only warm whites is not good for growing most plants, try to find a cool white or daylight tube for growing on your seedlings or adult plants,
4. Your shoplight is unlikely to scorch most seedlings unless they actually touch the tubes. But watch out and move the tubes further away if you see dried tips or leaf edges. The sun is more likely to burn them.

So what CRI # should I be looking for for my indoor lighting if I want to do more than just maintain my plants? I want the spectrum to be as close as possible to the natural daylight - should I be looking for a # higher or lower than 70?

Thankyou

I want the spectrum to be as close as possible to the natural daylight

Do you? Why? This is not necessarily a useful goal. Plants grow well under lamps with low CRI. The only major downside is that colours of, for example, flowers may not be as pleasing to the eye. Most of the time, your goal should be to get sufficient light intensity for the best growth. Only for relatively low light plants, perhaps for specialist growing like African Violets or Orchids, would I recommend you fo searching for fluorescents with a very high CRI.

A higher CRI means a more continuous spectrum. Lamp sellers would have you believe that a CRI near 100 is just like natural daylight but it really isn't. Perhaps at some stage you will have the opportunity to compare a high-CRI fluorescent lamp with natural daylight, not the same at all. They simply have a continuous spectrum, colours appear more authentic, and some people swear that their plants do better with them.

Anyway, there are many triphosphor fluorescents with CRIs in the 80-85 range, you may well want to use these since they are efficient, widely available, and not particularly expensive. The next step up is a CRI of 90 and above. These are specialist tubes, the price reflects that, and any gains in plant growth are minor. I'm not aware of any fluorescent with a CRI above 98, but that is so close to 100 that really there is no point looking for anything higher. These lamps are very nice on the eye, side by side with a standard triphosphor you may be so impressed that you'll never want to go back! No more grey flat light from that fluorescent :)

Well, I will be using them mostly for hoyas, and I believe I read that somewhere, about it being as close as possible to the natural light. I am not concerned about the hoyas flowering, I just want to keep them growing, as my living situation in this low light home ( too many trees around ) is only temporary.

Thankyou for your advice, it was very helpful.

Ines

Check out the Rensselaer Polytechnic Institute article on "Full Spectrum Lighting". "Full spectrum" has been the marketing-hype term for "natural daylight" for years, as there is no real definition for it in the lighting industry.
http://www.lrc.rpi.edu/programs/NLPIP/lightingAnswers/fullSpectrum/comparisons.asp
Definitely use the PREVIOUS button to view other info in this article.

Oddly enough, natural daylight (at what ever location on the planet, time-of-day, or season) is NOT the optimum spectrum for plants. Some wavelengths of light which are not being used by the chlorophyll are detrimental to plants. UV(ultra-violet) is especially damaging, as it begins to carry enough energy to actually bump electrons out of position - enough to break molecules apart.

Luckily, plants produce pigments whose sole function is to absorb UNWANTED light frequencies. For pigments and absorption wavelengths, see: http://www2.mcdaniel.edu/Biology/botf99/photo/p3igments.html

Zink

Here is a link that might be useful: http://www.lrc.rpi.edu/programs/NLPIP/lightingAnswers/fullSpectrum/comparisons.asp

Hey zink, are you affiliated with McDaniel College by any chance? It's just a couple miles from my house.

Watergal,

Nope, I live in Louisville, but I really liked McDaniel's educational site. I have a large collection of links and PDFs that I use for references. Until you asked, I didn't even realize what college I had referenced in the link.

From my readings, I have a great understanding of plants in general, but I do not have much experience with specific species. I always notice your advice seemed to have a basis in specific plants. After reading your page I understand why. You appear to have had a lot of experience. I also saw the photo of the Banana Tree incident. Too bad!

Speaking of storm damage, I would have responded sooner, but a lightning storm here in Louisville, KY disabled my modem. My computers were off, but the lightning was too close. I watched lightning hit my backyard fence twice within 15 seconds - with a lotta sparks! I had 4 kittens hanging out on the back porch during the storm and they sat and watched the lightning as if they were fascinated, and not a bit scared. They flinched at the closer hits, but just stared at the lightning, while chasing blowing debris.

As you know, most of my advice here had been electronic. I am both self-taught and took classes at the University of Louisville. I know you had said that you did not lean in that direction when I wrote how to overdrive some fluorescent lights. I always wanted to tell you that the particular shoplight, from Home Depot, which I had recommended for that purpose is also a really great, dependable fixture even without overdriving. I can't recall the exact model number at the moment (Commercial Electric something), but that particular fixture works great.

Zink

zink, thanks for the response. That storm must have been something to watch - can you devise a way to harness all THAT power for indoor lights?! Sorry about your modem.

I'm pretty much self-taught in gardening. I do read like crazy, and have been through most of the library's plant books, as well as having nearly a bookcase of my own. The internet has been a great learning tool for gardening, starting with GardenWeb as well as lots of other sites. Hanging out with coworkers at the garden center and my present job has taught me a lot too. I think caring for plants is both a science and an art. Did you ever see the movie "The Horse Whisperer"? I sort of think of myself as a "Plant Whisperer". I try to think like a plant, and yes, I do catch myself talking to them and even threatening or complimenting them sometimes.

I'm pretty terrified of electronics (although I did let Dell tech support talk me through opening up my laptop and trying to fix it - ended up needing a tech visit for the second fried motherboard in under two years, but that's a story for another time).

I have to decide what to do about shoplights this fall. Most of my plants are now quite large, and the small ones are either cuttings being rooted or low light plants I've propagated from cuttings brought home from my job. They do just fine on a table in the same room as the HID light, getting spillover light. If I do end up replacing some shoplights, I'll look for the Commercial Electric ones - are they T8's or T12's?

Outdoor sunlight is CRI 100, color temp of about 5500k. The lower the CRI, the farther away from natural sunlight.

Plants only use red and blue light, that's why grow lamps are optimized to produce red and blue (and appear purple).

Plants tend to flower if the red content is increased relative to blue, so if you want them to grow and not flower, use a light with high blue content such as metal halide, when you want them to flower, switch to light with high red content like sodium vapor.

Red phosphors are expensive, consequently most fluorescent lamps tend to have little red output but put out more orange, and then by putting out also more green, they appear more white; but plants use neither orange nor green.

Grow lamps put out mostly the red and blue plants need, but since other colors are missing the plants will not be rendered in natural color to humans.

Here is a link that might be useful: Future Sustainable Living Blog

Your K&B lamp is good for putting out lots of photons, but they are kind of weak in the blue end of things, which is required for synthesis of chlorophyll. I was finding the leaves on my rose cuttings were kind of pale under a 3000K fluorescent, so I added a 5000K (Ushio T8's) and that helped the leaves to develop a much more dark green color, telling me that the leaves were now developing chlorophyll more effectively. Some other plant species may do very well with just K&B however, so results will vary. Use your grower's eye and experiment, then report back. CRI is not important for growing plants, and all fluorescent lighting comes out in a "spiky" distribution, as does all HPS and all Metal Halide, although USHIO does make a very special fluorescent with a very broad spectrum, except that lamp is kind of low on lumens, so I'm not sure how effective it would be as a grow light - you could try it, businesslights.com does carry them. The mixture of rare earth elements and phosphors and the ratios determine what the lamp looks like to a human eye. The best lamp that simulates sunlight is actually a Phillips colormaster Ceramic Metal Halide, that runs off a standard HPS ballast, and it actually is a pretty decent overall lamp for growing. It has a CRI of close to 100, although for plants that is not important. It does have far more red component, which corresponds to a peak in the chlorophyll absortption curve, which is nice, it's cheap enough, ($53 for a horizontal 400W) doesn't need any special equipment, has good lumens, good maintained lumens. However, since you're using fluorescent, like myself at the moment, find a high output daylight spectrum lamp to supplement the blue component and you may find your plants do better - mine did. Sativa.

Here is a link that might be useful: a place to look for Phillips colormaster lamps.