OK so I thought its all about the color temp on the kelvin scale when it comes to lighting? Ive been going back and forth about using MH/CFL/T5 for my new grow space that im building. Ive just found out that 400 MH color temp only shows 4000 on the kelvin scale, but lumens are 36,000. 23w CFL are 6500 on the color temp which I thought plants respond most to but lumens are about 3600-3900 each bulb. Which is it plants respond better to, what is really the most important when looking for lights, Lumens or Color temp? Ive never seen a bulb yet thats 36,000 lumens and 6500 color temp.
So I pretty much just found this and I like to share with others who are lost in there thoughts about what type of lights to choose for there grow.
Kelvin rating and lumens does not equate for plants. The Kelvin scale is more of how your plants will look to you/us and is totally subjective. It is true that the lower Kelvin ratings like 3000K will have more red light and a 10,000K will have more blue light. Lumens are meaningless for plants, as green plants do not utilize green light for photosynthesis. A higher lumen rating at the same wattage often means greener light. Lumen is a rating weighted entirely towards human perception. It has little to do with the value of a light for either growing or viewing plants.
The Kelvin rating is an indication of color temperature. The higher the temperature, the more blue the light. Here's a rough scale:
- Reddish/Yellowish Endpoint -
Incandescent Light: 2700K
Blue Sky: 10,000K
- Blue Endpoint –
Don't be fooled by color temperature as an indication of what wavelength of light may or may not be present. The emitted wavelengths of light for two bulbs with the same color temperature could be wildly different. Therefore, color temperature is not what you should use to determine useful light for growing plants. It will, however, give you an idea of how things in your grow will look. For example, the sky has a color temperature of 10,000K and looks blue. Lighting that has a higher color temperature, indicating that it is bluish, does point to the fact that blue wavelengths are dominant. This, in turn, just means that it will activate green plants in the blue range, which is a good thing. Red photosynthetic pigment is less efficient at utilizing light and requires stronger light as a result. The less efficient red carotenoid pigment must rely on blue and some green light as well as more intense lighting. There are some plants that that are able to change the pigment they use for photosynthesis depending on available lighting. We see this in red-leaved plants that turn green if the lighting is too low, not enough blue and/or green light. Alternatively, some green leafed plants produce red foliage when closer to the light source or with overly bright lighting.
The Kelvin color designation of a particular bulb is not always true to the black body locus line on a CIE Chromaticity map. This is why some 5000K bulbs look yellow and others white, especially when trying to compare a linear fluorescent with a CF or MH. This is where Kelvin ratings of bulbs can fall prey to marketing schemes/hype.
The standard measure that quantifies the energy available for photosynthesis is "Photosynthetic Active Radiation" (aka "Photosynthetic Available Radiation") or PAR. It accounts with equal weight for all the output a light source emits in the wavelength range between 400 and 700 nm. PAR also differs from the lumen in the fact that it is not a direct measure of energy. It is expressed in "number of photons per second". The reason for expressing PAR in number of photons instead of energy units is that the photosynthesis reaction takes place when a photon is absorbed by the plant; no matter what the photon's wavelength is (provided it lies in the range between 400 and 700 nm). In other words if a given number of blue photons is absorbed by a plant, the amount of photosynthesis that takes place is exactly the same as when the same number of red photons is absorbed. This is why it is so important to get the spectral output of a bulb before deciding if is a 'good plant light'. You may need to add/mix bulbs to get a lighting that has good visual effects for the human eye and proper light for plants because 'plant bulbs' tend to be purplish. There is an additional term called "Photosynthetic Usable Radiation" or PUR which takes in to account blue and red light only.
I don't understand why people insist on distinguishing between lamps on the basis of their color temperature. No lamp renders color correctly or looks natural unless its Color Rendering Index (CRI) rating is very high. When CRI is over 90 the color temperature shouldn't make much difference; colors rendered accurately will always look about the same regardless of the Kelvin rating. Many bulbs render red and orange colors poorly and give you a look with very flat color contrasts. Other bulbs produce a lot of green light and don't render either blue or red very well at all.
CRI or Color Rendering Index is an indication of how close the light is to daylight (full spectrum) on a scale from 0 to 100 with respect to how it makes objects appear. In the case of the Philips PL-L 950, the CRI is 92, so it has pretty good color rendering properties. Two bulbs with the same Kelvin temperature but different CRI ratings can produce very different appearances. Compare a 5000K that has an 80-something CRI with a 5000K that has a 90-something CRI. The 80 CRI bulb is very bright, but it renders greens with a distinct yellow cast. The 90 CRI bulb is dim, but it renders rich colors across the whole spectrum.
Whether or not a bulb looks "natural" to you is totally subjective. It depends in part on what you're used to. If you only see the world under cool white fluorescents then that is probably what looks natural to you. If you live somewhere with frequently hazy or overcast skies then you may be accustomed to "natural" light having a color temperature near 7000K. If you live somewhere with clear skies and infrequent cloudy days then your natural light might have a color temperature closer to 5000K. If you are used to north skylight then maybe a color temperature close to 10,000K seems more natural. In any case of actual natural light the light will render colors pretty well. That is usually not the case for fluorescent lamps with a high Kelvin temperature rating. If you want a high K lamp that does render colors accurately then you might try finding the Philips C75. It has a 7500K color temp and a 90+ CRI. It could be hard to find and a bit pricey.
Plants will grow with ordinary bulbs as they tend to have both some blue and red emissions. The problem is that they also have wavelengths between 500 and 600nm, which algae likes. Green algae and green plants use the same pigments for photosynthesis (chlorophyll a/b & carotenoids). So, light that helps one helps the other. The algae that are different are the blue-green algae (cyanobacteria), which contain Phycocyanin and absorb light heavily in the low 600nm (orange-red), which is unfortunately present in most standard fluorescents. Strong blue light will cause plant growth to be more compact and bushy.
Bulbs sold as generic plant/aquarium bulbs usually have OK energy in blue and not much in red. A bulb sold as a generic "sunshine" bulb may or may not have some useful red, depending on the bulb. You can put any fluorescent lighting on your plants and do OK, but if you want to maximize plant growth, it's best to compare lighting options and, if possible, try to find the graphs/data for spectra output, rated life and output decay over time. Unfortunately, CF bulbs haven’t caught up with linear bulbs in the ability to offer light (tri-phosphor type) in the proper areas of the spectrum.
Fluorescents lose efficiency over time. Some lose more than others - some bulbs may only suffer 10% drop in output, while others may drop 30% or more in the same time frame. The less the drop over time, the less you have to replace them, depending on your application. Linear fluorescent tubes should be changed out every six months and compact fluorescents every year.
Fluorescent bulbs marketed for aquaria are often more expensive and not necessarily better than generic versions. They are also not necessarily marketed correctly. Many bulbs offer spectral output graphs. However, many of these graphs are measured in relative power on the Y-axis rather than a known reference like watts per nanometer per 1000 lumens. All that 'relative power' lets you know is that 100% is the highest peak at a given nanometer and all other peaks are relative to this. So, don't be fooled by nomenclature and packaging (marketing hype).
If you get a CRI in the 80s, you're doing fine. This is only a measure of how much something looks (to humans) under the bulb light as it would under "normal" light.
Any fluorescent will work, but triposhphor (aka sunlight, full-spectrum) bulbs seemt to work a bit better, covering more parts of the spectrum. Plants aren't allthat fussy about the spectrum except that regular fluorescents have strong output in the green part of the spectrum and plants reflect much ofhte green light back. Lumens are the visible (to humans) light so if two bulbs have the same lumen ratings and one looks brighter, the "extra" light might be only what humans see, not what plants like. Unless there is a big diff in the green part of the spectrum between bulbs, it doesn't matter than much to plants.
Color temp gives only a rough idea of how things will look under the light, whether there will be a strong blue aspect to the white light (higher temps) or yellowish or reddish. Actually, they only give a ersatz measurement of the overall spectral output, not how the light will look. They don't tell one much about spectral output, just the overall value (the sum of the peaks and dips in the spectral output.) Diff spectra can have the same color temp and even appear to be a somewhat diff hue. A high narrow peak in the blue region will pull up the color temp rating without making the light seem much bluer. A slightly depressed but wide slump in the red region will raise the color temp but so will a a deep narrow slump in the red and green. So high color temp doesn't always mean bluer or low color temp mean redder. Note that the color temps are different shades of white, not say blue vs red bulbs. And note that plants don't seem to mind much about color temp ratings. Get what looks good to your eye-- otherwise don't worry about color temp.
You probably won't find standardised PAR ratings on enough diff bulbs to be able to make comparisons. But PAR tells you how much light the bulb makes that some plants can use for photosynthesis -- so everything else being equal, higher PAR means more light for the plants. It's usually not hard to get enough light over plants, so PAR isn't terribly useful for making crditical determinations between which bulb to buy, especially since it is such a uncommmonly available rating.
If you see bulbs you really like the look of, you can grow plants just find with those bulbs, even if they are cheap old shop lights. Triphosphor, full spectrrum/sunlight bulbs generally will have a more "sunlight" appearance -- although some made especially for aquaria can be kind of purplish due to big spikes in the red and blue parts of the spectrum. Personally, I think purple and pink bulbs belong on Christmas trees, but it's a matter of personal choice.
Watts is a measure of the amount of energy the lamp consumes, assuming you use a particular standard ballast under standard conditions. What are the standards? They are pretty much whatever the manufacturer used to rate the bulb and somnetimes you can look them up, but usually not. So watts ratings don't tell you the actual light output of a bulb or even the actual watts that it will consume, but it will be reasonably close on the energy consumption.
So when your out shopping for bulbs, try to find bulbs in the 6500-5000k (w/ 5500k the best) aka "FULL SPECTRUM" or "DAYLIGHT" bulbs for vegging, that have a high CRI, the higher the better. I would recommend looking at these bulbs: Duro-Test Corporation's Vita-Lite (c) and Vita-Lite Supreme (c). The original Vita-Lite hit the market in 1967 (!) as the world's first patented, natural-daylight-stimulating fluorescent tube. For over twenty five years (until the advent of their Vita-Lite Supreme) Duro's Vita-Lite was the closest simulation of natural daylight ever created by anyone, anywhere. (No, I'm not being paid for this plug) Specifications: 5500 K, 91 CRI, 2180 Lumens. For folks looking for more luminosity Duro-Test offers another lamp, the Vita-Lite Plus; the only specification difference being the generation of 2,750 lumens. The Vita-Lite Supreme offers 5500K, a CRI of 96 at 2000 lumens; it is the best match yet to natural outdoor light. These are great (the best available) lamps for the marine aquarist, aquatic gardener, herptile keeper, photographer wanting to skip filters, and human work place. They grow aquatic organisms better than any other light system, without specialized fixturing at the lowest cost. What is more, your fishes and photosynthetic organisms look and live better under these lamps. Yes, these products are that good. You can reach Duro to find your nearest dealer by dialing 1-800-289-3876. Also, in all fairness, I'd like to mention three other manufacturers of full-spectrum fluorescents. They are Philips with the Colortone 50, General Electric with their Chromaline 50 and Verilux with lamps of the same name. These companies also 'private label' full spectrum lamps for other labels. You will have to look for the CRI, Temperature in Kelvin, Luminosity in lumens, power curve, and average life ratings to make your own consumer judgments. As far as flowering bulbs go, 2700-2100k, you probably wont find a bulb w/ a CRI over 82 in CFL'S or Flouro's, & even lower in HPS at around CRI of 22.