Discuss - Kelvin And Spectrum

[aaronnorth]

Hi all, i update everybody with the discussions that has been going on about Kelvin and spectrum. My view is that It doesnt matter what kelvin is, plants will grow under it and that spectrum is far more important.

aaronnorth: Plants will grow under any Kelvin rating, they are not to bothered. The Kelvin values of bulbs as well as the "best" term (5500k - 11 000k) have only to do with what you like to see, not what the plant is capable of assimilating.

colour spectrum and kelvin are different, here is a section of the guide i have written on the UKAPS forum:

(KELVIN) - This is the colour of the tube’s output measured in degrees Kelvin (K). The 'best' colour temperature for plant growth replicates daylight at around noon on the Earth’s equator and is approx. 5500K to 6500K. This is a white light and is normally produced by full-spectrum lamps. There are other tri-phosphor lamps available which give varying colour temps ranging from 3000K to 10000K. The lower the colour temperature the redder the light, the higher the temperature the bluer. I have heard of and experienced success stories with a wide range of colour temperatures. I would recommend having a K between 5500k – 11 000k, but to be honest as long as there is enough light, then don’t worry to much about the Kelvin, The spectrum is far more important (Red, Green and a bit of Blue).

(SPECTRUM) - Widely regarded as the best light for growing aquarium plants is the full-spectrum lamp although no data has been provided to support this. This means that the light output peaks in three (regular T8s peak in two) colours giving a “fuller” light more likely to meet the plant’s photosynthesising requirements. Photosynthesis occurs most efficiently with peaks in the red, green and a bit of the blue parts of the spectrum. Plants are adaptable and will change their pigment distribution and content to adjust to the available spectrum. Most full-spectrum lamps will give a cool white light, ideal for both plants and for viewing and will have a high Colour Rendition Index (CRI) meaning that the illuminated objects will appear in their natural colour, these tubes are not produced for plants, but for the human eye, it is what looks best to you.


also take a look at this thread: <a href="http/www.fishforums.net/content/Plants-a...is-thread-too-/" target="_blank">http/www.fishforums.net/content/Plants-a...is-thread-too-/</a>

and at the pinned article at the top of this page.

boboboy: as you are going against, current scientific knowledge with the comment that the kelvin rating of a light source has nothing to do with plant growth, do you have any scientific evedence of your comments? i would be interested to see it. as most of the papers that i can understand indicate the plant growth is added by lights in the full spectrum range of around 6000k, which is also interesting as you seen to think kelvin and the spectrum are different things!

aaronnorth: I personally dont have evidence, but i have been able to grow plants with 18 000k. very few if any aquatic plants ever see full spectrum midday sun, since they grow under the canopy shade and under murky waters in the rain forests of the world, rendering the value of Kelvin temperature out. The only reason it is reccomended to have 5500 - 11 000k is that the colour isnt too red or blue, it has a truer CRI which is better for us.

I also found this:

When describing a light source as having a Kelvin rating, it refers to a light source that emits energy across the entire visible range from 300 to 700nm. Sunlight and incandescent lamps are very good "Black Body Simulators"- they behave in a manner very close to the predictable spectral distribution of the "Theoretical Black Body Radiator." With these light sources, one need only measure the energy at two places in the spectrum - red and blue - to determine the Kelvin. However, when the light source has an "interrupted" spectrum - as do all fluorescent and discharge lamps - it is not correct to describe that light source as having a Kelvin temperature.

source - [URL="http/www.cameraguild.com/technology/kelvin.htm"]http/www.cameraguild.com/technology/kelvin.htm[/URL]

aqua glo, 18 000k

power glo, 18 000k

As you can see they are both different spectrums, but the same kelvin - also, the aqua glow is pink to the eye, and power glo is white to the eye.

I want someone else to comment as at least 1 of us has to be wrong

Dave Spencer: Nobody I know of in the planted tank hobby that knows how to grow plants reports any difference in growth in plants in different renges of the spectrum. Plants may look different colours under different lights in the same aquarium. Prune them, take them out, and both plant cuttings look the same in terms of health, internodal distance etc.

The emitted spectrum of the sun varies throughout the day, as do periods when plants become shaded. It doesn`t make sense for plants to adapt to a specific part of the spectrum when it is constantly changing. A lot of people in to planted tanks realise that plants adapt to the light available to them...our very own Sun has dictated this.

Buy lamps that have a good CRI (basically, what looks good to your eye). I go for CRI and intensity (I use my own experience to judge growth rates via this) to grow plants, nothing else. Fortunately, this means I know I can go to lampspecs and buy a variety of daylight tubes to experiment with for the best look, all for the price of one so called plant tube from the likes of hagen etc.

No scientific papers. Thay are not needed when all we have to do is observe our tank life.

Dave.

boboboy: humm, interesting. the statement was

kelvin doesn't matter, it is just another thing to try and sell you a tube, spectrum is far more important:

put at its most simplistic, the kelvin rating is simply an indication of the number of light wavelengths, from the visible spectrum, that can be seen. the higher the kelvin number, the more there are. up to a reading of around 5500-6000k. this is considered and "full spectrum" lighting, and as such is what it says on the label, all the wavelengths in the visible spectrum are there. we are all aware that plants require differing light types to grow effectively, some need, for the most part, light from the lower end of the scale, even so many also need light from the upper reaches too. often plants need light of 900nm but the same plant also needs 320nm, the only way to provide both is to have a full spectrum light. now the argument that the kelvin rating if the bulbs may well be faulty, if not down right incorrect, is well founded, i found one tube rated at 55,000k, I'm not even sure that is possible!

now this "get a light you like the look of" thing. granted you may well be able to alter the hue and colour saturation of some of the colours in the tank, with different colour lights. however the overall view, for the human eye, will convert the colours until the look like they were viewed in day light 5500K. this is an automatic reaction we have no control over. so within seconds of switching on your new lights they will look, to you, just the same as they did with your old lights. this is a fact not my thoughts, and is well beyond any argument. its like your eyes, well your brain, have an automatic white balance system just the same, though more advanced, as your digital camera but we cant switch it off.

so plants need a broad range of light wavelengths for healthy growth. now unless you install single wavelength lights to satisfy the plants requirements, you need to provide a light that hold all the required wavelengths. the best way to do that is to offer full spectrum light. how do we do that? by using bulbs with a kelvin rating of 6000k, or there about. now the rating may not be accurate, that is another story, but to dismiss the kelvin scale as, simply, a sales tool, is at best strange, and at worst shows a lack of understanding about what it actually is.

looking at your graphs, aaronnorth, i see your point, though there is a simple explanation. though stated as 18,000k, in all probability the figure is rounded up and down. so the first chart could have a true Kelvin rating of 18,004k and the second 17,998k, though be lumped under the banner of 18,000k. a simple explanation for the difference between the two spectrum charts.

and that is where we are as of today! Please could everyone chip in on their views, we need more evidence/ suggestions!

Thankyou, Aaron

 

[raptorrex]

indeed so, thoughts anyone?

 

[Wolfenrook]

Well, for one thing it's pretty difficult to divide kelvin from spectrum. The kelvin of a tube is basically the colour temperature of the light, oh look, spectrum! lol As in the spectrum of light given off by the tube will actually decide the colour temperature. So frankly discussing which is the most important is a bit on the silly side. The divide though seems to me to mostly be thanks to manufacturers, on some tubes they just give you the colour temperature in kelvin, whilst on others they give you a detailed breakdown of the spectrum of the tube. At the end of the day they are the same thing, they both tell you the colour of the tube, one is just more detailed is all.

No, the most important factor of lighting for plant growth is actually LUMENS output, as in how much light the tube actually emits, regardless of the colour. lol

Ade

 

[Renate]

I am confused.

I had 3 light tubes over my tank. Two were greenhouse tubes 17watts. One was philips daylight tube. Majority of my plants were not growing very well under this light. One blew out thus added a light by currentusa. Now have 1 t5 65watt over my tank and all of the plants are growing.

I think spectrum is the most important aspect of a tube for plant grow but it is not always listed on a bulb. Thus I go by the Kelvin.

I read that a high CRI means you have a lot of green light which is great for view but doesn't help the plants grow.

 

[aaronnorth]

CRI is irrelevant to plants, it is just what humans percieve. Thanks for yoiur answer Ade

the most important factor of lighting for plant growth is actually LUMENS output, as in how much light the tube actually emits, regardless of the colour.

well i was right on that one lol that is what started it off in the first place

 

[lljdma06]

CRI is irrelevant to plants, it is just what humans percieve. Thanks for yoiur answer Ade

the most important factor of lighting for plant growth is actually LUMENS output, as in how much light the tube actually emits, regardless of the colour.

well i was right on that one lol that is what started it off in the first place

You know, I look at the color temperature, but when I tried to actually follow recommendations and put straight 6700k in my tanks, it looked aweful. Very yellow to me, so I always blend with a colormax bulb (color enhancing) of some type, which for some reason, never gives a color temperature on the package. The result, a very pleasing lighting, at least for me. For all I know, the colormax 's color temperature could be way off what is normally recommended. You know what? The plants still grow, and grow well. I agree, Lumen output is most important, which is why I no longer use T8s. That, and the fact that those things are just massive in comparison to T5s and compacts. Very unwieldy.

I was very curious about the portion of the quoted discussion that touches on the human eye adjusting for whiteness. I'm not sold on this yet for I find that my eyes are extremely sensitive to the "color" of the light and I'll still notice the difference days later. That being said, I have severe Myopia and an astigmatism. Glare and light levels can effect me a lot, so maybe I am more senstive to subtle light changes than others and the parts of my brain and eye that would naturally adjust the white balance may not work well. That is entirely possible and would account for this. I am defective.

llj

 

[Wolfenrook]

Llj, I find that the 'plant' tubes (Sylvania Grolux is probably the cheapest of these) are very good to use to balance the yellows and greens of daylight tubes. They have a similar pinkish tinge to them as colour tubes but seem to be a bit 'brighter' as well. Laying things down straight I have always found the best combination to be a mix of 6500k daylight with a plant tube. Many have also had success with 10,000 k, but I find that these make my tank look 'cloudy'.

Ade

 

[lljdma06]

Llj, I find that the 'plant' tubes (Sylvania Grolux is probably the cheapest of these) are very good to use to balance the yellows and greens of daylight tubes. They have a similar pinkish tinge to them as colour tubes but seem to be a bit 'brighter' as well. Laying things down straight I have always found the best combination to be a mix of 6500k daylight with a plant tube. Many have also had success with 10,000 k, but I find that these make my tank look 'cloudy'.

Ade

What's wierd though is that the 6700 and 6500k are my plant tubes, at least according to the packaging. They are not pinkish at all. The colormax is the pinkish bulb, so perhaps they have a better color temperature and spectrum than the so-called plant bulbs. I tried double colormax once too, that was too purple. The anubias looked almost metallic. Really strange. At any rate, a balance is what works for me too, though to save a buck, I'll check out your suggestion. Yeah, I don't like the 10000k either, it does make the water appear cloudy. A 10000k bulb came with my Compact Flourescent fixture and since it was a free bulb, I tried it out. Didn't like and the fish were so washed out.

 

[Wolfenrook]

Could be they label things differently over there? Over here 6700k and 6500k are usually labeled as daylight. The sort of tubes I am thinking of are ones like the ZooMed FloraSun (T8), Sylvania Grolux (T8 and T5HO) and the Aquamedic Planta T5HO. I have an Aquamedic Planta (bought before I saw the, uhm, light and started buying normal brand tubes) in my luminaire with 2 Osram Lumilux 865s and a single 10,000k (which I want rid of because even 1 makes things look cloudy. Waiting till we have more money though as the plants are growing great even with it. lol), it does an excellent job of balancing the greeny yellow colours from my lumilux 865s but seems more intense than the colour tubes (in T8s I found that the ZooMed Flora Sun did the same job). Makes my fish sparkle when they are under that one as well.

Ade

 

[raptorrex]

I was very curious about the portion of the quoted discussion that touches on the human eye adjusting for whiteness. I'm not sold on this yet for I find that my eyes are extremely sensitive to the "color" of the light and I'll still notice the difference days later. That being said, I have severe Myopia and an astigmatism. Glare and light levels can effect me a lot, so maybe I am more senstive to subtle light changes than others and the parts of my brain and eye that would naturally adjust the white balance may not work well. That is entirely possible and would account for this. I am defective.

llj

lol, you may well, have more sensitive sight! try an experiment. take a picture with your digi camera, take the picture under house lights, with the white balance set to daylight. now look at the picture you have taken. it should look very orange, or warm would be the correct term, this is not how you see the light though, is it? to the human eye, the light looks far cooler (more blue). at its most basic this shows how the brain corrects the colour of light we actually view, into the colour we actually see! as an aside to this though, the ambient light will also change how the colours in your tank look, it actually happens by the same mechanism. a good argument could be made to say that changing the ambient light colour(temperature), may well have more effect, to the human eye, than changing the colour temperature of the tank lights.

as for the effect of light wavelengths, on the growth of plants? well there is a wealth of scientific, and impractical evidence that the wave length's of light are one of the most important factors in the growth of plants. i fully agree that both, duration and intensity have an effect, but that was not the comment, the comment was that the kelvin rating ( the range of the visible spectrum, emitted) has no effect on plant growth. now if i have misunderstood the comment, and what was actually meant was, that the kelvin rating of bulbs is so inaccurate as to make buying one on the strength of it, a waste of time. i may well fully agree. but if the comment was meant as it was read, nobody has offered anything, here, that would justify ignoring the current, commonly held, thoughts that colour wavelengths avaliable to plants have a vital part to play in their growth.

 

[Wolfenrook]

nobody has offered anything, here, that would justify ignoring the current, commonly held, thoughts that colour wavelengths avaliable to plants have a vital part to play in their growth.

Probably because that wasn't the question asked at the start of this thread. The question asked was what is more important, spectrum or colour temperature. As I already said you can not remove the colour temperature from the spectrum as it is the spectrum that will define the colour temperature. A widely split spectrum will give you a 'daylight' temperature of about 6,000-7,000k, whilst a spectrum that peaks more in the blue is more likely to give you a temperature in the 10,000k range.

If however you want your question answering, then the simple answer is that the best colour wavelengths for plant growth are going to depend upon the individual plants. Green plants prefer light at the redder end of the visible spectrum, whilst red plants use a greater range of wavelengths (including UV, which is one of the reasons that these plants do better with very intense lighting that is closer to daylight). In the average aquarium however we grow a mix of these, and so LUMENS actually becomes far more important with a need to provide as broad a spectrum as possible, hence the popularity of 6,500k daylight tubes in planted tanks. Both anecdotal and experience tells us that plants do very well under 6,500k tubes, and that the main factor that we aim to improve if anything is the intensity of this lighting. You can try all you like to grow high light requiring plants with a lower intensity with your idea of a perfect spectrum for that plant and it just wont work. Take the same plant and give it a more generic daylight spectrum but at a higher intensity and it will (given adequate nutrients of course) flourish just as well as if you grew it under a higher intensity of your cherry picked wavelength. Factor in the simple cost to efficacy equation and specialised spectrum so called plant tubes become even less attractive.

You want to know what light plants (usually) grow best under, go to the plants natural growing environment and take a look, and surprise surprise you find good old daylight, usually for the majority of the day somewhere between 6,000k to about 10,000k (not counting sunrise and sunset here) (ish) which if you break it down will at various times of the day have a wavelength that peaks at just about every colour.

To summarise, the best wavelength to use for growing plants is pretty much ALL of the visible ones at some point, which makes intensity the more important factor as you are already providing as many wavelengths as possible.

Ade