Your 6500s have a little red spectrum in them it's not all blue. I'm really starting to think that this switching to 3000k to make plants bloom is a gimmick. My pea plant flowered and fruited under 6500 only, LEDs use mostly red spectrum so does HPS and plants do not flower until they are ready to do so. I believe that light light duration(how much dark time their getting), intensity of light, plant's growth stage most of all and change in air temperature trigers flowering. As far as Photosynthesis goes those red flourescents as not as benefitial because they don't produce the ultimate red spectrum so you're better of with the 6500 IMO.

Personally, I don't think your plants will care either way. With three 6500k & one 3000k bulb in your fixture, I don't think your eyes will see much of a difference either. I strongly agree with the above poster regarding 3000k making plants bloom (being a gimmick).

You're probably already aware of what Kelvin is all about (e.g., 6500k). Just in case you are not... kelvin rating is the hue of the color temperature, expressed as a measurement in degrees kelvin. I think of kelvin this way: 2700k is late afternoon color light, a few hours before sundown. 6700k is noon color light on a blue sky day at the equator. Bulbs with a higher k rating give off a cooler, crisper blue light. Bulbs with a lower k rating emit a warmer red/yellow color. Most people assume that since 5,000k to 10,000k resembles daylight, then it has the same properties (which is not true).

Kelvin rating has more to do with appearance. Photosynthethically Useable Radiation (PUR) is a more important factor of how well a particular "light" grows plants. Basically, PUR is the output of light needed for photosynthesis. Plants also prefer specific spectrums. You can calculate kelvin ratings from the spectrums, but you can't know spectrums based on the kelvin ratings. 5500k is typically referred to as full spectrum because it contains a blend of all colors through the spectrum.

Photosynthesis uses a lot of the 650-670nm light spectrum (appears to our eyes as deep orange to red), and also uses much of the 430-475nm range of the spectrum (various shades of blue). So... what should you look for in a bulb if kelvin rating isn't the best measurement for growing plants? Spectrum!

Most bulbs will usually have a spectral power distribution graph from the manufacturer. Good plant growing bulbs will have higher concentrations of light output in the 430-475nm range, almost no output in the 500-600nm range, and another spike in the 650-675 range. If the graph looks like the letter M (rising in the 400nm range, falling in the 500nm range, and rising again in the 600nm range) it is probably a good grow bulb.

Included some pictures (LEDs used for growing Tillandsia indoors). It will give you an idea as to what some of the kelvin temperatures look like, along with what they look like over the plants. Does one work better than the other? Personally, I've observed that the mixture of 6000-7000k & 660nm has been 'a bit more favorable' for growth, flowering and reproduction.

4500 to 5000K
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6000-7000k
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6000-7000k & 660nm red
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Tillies under 4500-5000k
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Tillies under 6000-7000k
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Tillies under 6000-7000k & 660nm red
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Tillandsia ionantha 'fuego' flowering under 6000-7000k
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This post was edited by o2tiller on Wed, Aug 21, 13 at 2:10

The closest fluorescent bulb to the optimal red that I've seen is called a Red Sun, it's in the 630 nm range. I haven't used it yet so I tell you if it's effective or not.
However , I believe that a better addition of red spectrum light to a fluorescent light setup would be implementing some good quality LEDs and I'm not talking about those $80 ufos :) good quality 660 nm leds with large heat sinks,60 & 90 degree lenses would make it worth it.

Somewhat off the original subject, but here is a 100w LED that would cover all of your spectrum needs (if you enjoy diy projects and are serious about using LEDs). Has 5 channels that can be individually dimmed. My guess would be that one of these would cover a 2 ft square area.

{{gwi:1028268}}

how much is this puppy? :) I wish I know how to work with electronics and would probably do such project. But don't you thing that it would be better for the leds to be spread out further instead of having them all in one spot?

O2tiller, those tillies are amazing , especially the flowering one.

Meanwhile, I got a 6500K buldb as replacement. Not ready for LEDs personally.

Thanks for the kind words, Greentoe357. The 6500k replacement is a good choice. I believe your 54w bulbs are t5ho. A four bulb t5ho fixture is a great fixture (puts out a lot of light, especially with good reflectors).

I've been experimenting with LEDs for a couple years. Was very skeptical at first, and knew the only way to find out how they performed was to get some 'hands-on', to be patient & give it time, and then the all important factor: observe how my plants react under LEDs.

I have used metal halides, T5HOs, power compacts, and spiral CFLs... all have performed well for my plants. I've been impressed with LEDs, but also still use t5ho (I like the quality of light & the spread t5ho produces). Once the LED industry (should be in the very near future) has finally nailed down a cost effective product that everyone & their brother can afford, I'll switch over completely to LEDs.

Slimak... you know, I'm really not sure what the exact price of the Lumia 5.1 is, but have been told they range about $90-100 a pop. A bit too rich for my blood (thought I was doing good being able to 'almost' afford Phillips Rebel ES and Cree XP-G for $3-4 apeice)! Seems like anything new on the LED market is very expensive initially, and then the price starts falling after a period of time (or when a new and better product comes along). I have not used these LEDs before, but would love to give them a try. If you had about half a dozen of the Lumia 5.1 spaced about a foot apart, you would have some very serious light. From what I gather from the people that I know who are using these, it's a small chip that packs a very serious punch (with very intense light and good spread).

O2tiller, you said:
>> A four bulb t5ho fixture is a great fixture (puts out a lot of light, especially with good reflectors).

What constitutes a good reflector? I bought this fixture (http://www.ebay.com/itm/261226369473) and am considering buying another for the next shelf down. Cost is important, as is the appropriateness of the light for people (this sits in my kitchen where I spend a lot of time).

Hi Greentoe:

What constitutes a good reflector? These are just my opinions for what it is worth.

Many times you will see a reflector advertised as increasing your light 100-300%. I believe the advertising should really say "this reflector will utilize almost 100% of your bulb" instead of claiming double or triple the output. You cannot increase your light output beyond the wattage of the bulb. You can increase your light levels (by what you had before) using a good reflector. Most people are trying to get more light down to where they want the light, using a reflector.

Good reflectors are based on the shape of the reflector, material used for the reflector, and the position of the bulb in relationship to the reflector (bulb/reflector spacing). Restrike, which reduces light intensity, will also be a factor.

A common problem with reflectors is their shape (e.g., flat top reflectors). Most of the light being emitted from the top of the bulb is being redirected and reflected back to the bulb. Also, any light that is reflected 'up' at other angles is being reflected back to the bulb. This ties into another important factor that needs to be considered; the temperature of the bulb when in operation. As the temperature of a t5ho tube rises, the overall light output is reduced (that's why a lot of fixtures have fans built in). Restrike will increase the temperature of the bulb.

IMO, good fixtures will use one individual reflector per individual bulb. One of the better materials used for a reflector is polished aluminum. One of the better shapes for a reflector is parabolic. Some of the poor performing reflectors have flat backs, and/or are very narrow where the bulbs are too close together so there is no room for light to travel around the back of the bulb. Here is a picture of a 2-tube reflector that has worked out well for some of my applications.

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My reflector shape seems very similar if not identical to the one on your picture. One bulb is missing on my pic so the reflector is visible both with and without a bulb. My fixture does not have fans though, just vents. Depth is 14 inches with 4 bulbs, which I think is in line with other similar fixtures and hopefully the bulbs are not too tight. I am leaning toward getting another. $88 price is the best I could find. Anything else I need to consider?

Greentoe357 you can further increase the performance by adding reflective material on the sides of your growing area so the light could bounce off it and back to the plants. Seems to be working great for me. Some surface painted with white flat paint, white color grow film or mylar if you like that. I went with Orca film. It is expensive but unlike mylar, it's sturdy so it doesn't create any hot spots nor flap when the fan is blowing on it. Also "supposedly" it disperses the light better.
Here is an example of what I did

6500K is fine. I have tried all sorts of lamps, including "full spectrum" etc., and basically 4100K is good, 5000K is good, 6500K is good. I also do a lot of growing under HPS which is just 1900K and even 1900K works great and I use metal halide 5000K lamps - and they ALL WORK FINE! I find that "full spectrum fluorescent" is a waste of money, and although it is more expensive, it gives smaller PAR readings. - paul m. the bloom and flowering marketing is just a marketing gimmick to get you to buy more lamps that what you need.

Slimak, good idea on the reflective film. My background / wall color is "apple green", so it's also good to make the foliage "pop" a little for visual effect.

:) yeah it does kinda blend in right now with that nice green wall. Also paint a sun on it maybe you'll fool the plants into growing quicker hahaha. I gotta try that :)