Lighting - Does Kelvin really matter??
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Old 06-10-2011, 06:18 PM   #1
aquagrl
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Lighting - Does Kelvin really matter??


So I've done my reasearch and have found such conflicting information about lighting... I really just want to know from experience how my plants will do!! I was at petsmart and they had hagen T8's on clearance...I have an eclipse system so my only option right now is two 20 watt T8 bulbs. I picked up life glo 6700k and Flora Glo 2800k...didn't realize the flora glo would give off a pink hue - it was the recommended bulb for plants, so I bought it. Doesn't look too pink with the 6700k but probably not the best choice to please the eye!! Now fpr my plants - does kelvin really matter? I've read that plants like the red spectrum which this does give off, but then I read that actual lumens are what the plants actually benefit from!!?? So confusing!! I have a 32 gallon clear for life tank (acrylic) 30" x 12.5" x 20" with 40 watts total - will my plants be ok??? I usually leave on for about 12 hours a day and dose with excel every 2 days or so. What lighting would you recommend, considering I have an eclipse and can't retro fit or swith out the tank or lighting at this time (budget-wise)...open to any suggestions, or opinions. All of my plants are very low light plants. Thanks!!!
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Old 06-10-2011, 06:36 PM   #2
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the high parts are the color (wavelength) that photosynthetic cells absorb to do their metabolic business. Most bulbs emit light across the spectrum ,with peaks in targeted places (reds/greens for plants, UV/blues for marine stuff). IF you had a build with the peaks in the wrong place, but was SO bright that the 'troughs' of the emitted light were high enough, you'd still grow plants.

You'd also grow algae like crazy; in my opinion - i think that algae is less discriminating than plants are when it comes to spectrum.

Wavelengths and kelvin are closely related.

Wavelength:


Kelvin: (not sure I agree with those labels for the lighting types, though..)


I would go with 6500K unless you're trying to grow something funny. Lots of folks combine different spectrum bulbs together, but I've not seem many people use anything in the 2000 range.
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Old 06-10-2011, 06:40 PM   #3
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looking at it closer, I really dont like that kelvin chart. :/
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Old 06-10-2011, 06:46 PM   #4
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Hello Aqua...

Having an Eclipse set up does limit your lighting. However, I've had larger Eclipse tanks and never had trouble growing basic aquatic plants.

The "K" or Degrees Kelvin rating is the measure of color quality. The higher the Kelvin number the more blue a light will look. Natural daylight is 5500 K, so any light in this range will do for your plants. I have a single 6500 K, T8 in some of my low light tanks and as long as I keep low light plants, everything does very well.

The Lumens is the measure of light energy put out by a bulb. If I'm not mistaken, higher lumens means a hotter bulb. I'm not up on lighting so much. I just look for a light in the 6500 K range and check what type of lighting a plant requires before I buy it.

B
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Old 06-10-2011, 08:18 PM   #5
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Hi aquagrl

Intensity is the MOST important factor. You can figure that out by looking at Hoppy's thread about PAR . After that you can start messing around with spectrum and Kelvin temperature. It turns out though, that the total photosynthesis in plants under water, from all the wavelengths, are approximately the same from all parts of the spectrum of light. Green/yellow light is only ~15% less efficient at photosynthesis than blue and red light. Here's a good quote I found :

"The fact that plants use the entire visible portion of the spectrum of light more or less uniformly allows for the selection of lighting based on aesthetics. Lamps with a color temperature of 6500K are better at color rendering than 5000K, because they have a better differentiation of blue shades - it comes from the fact that the 6500K color temperature is higher, and a higher color temperature means a greater proportion of blue and green spectrum. More green light will significantly improve all the subtle differences between shades of green and make the aquarium "brighter". Aquariums should prefer lamps with color temperature of not less than 5200K and a ratio of red / blue (R/B) ~ 0.6 with a slightly higher proportion of blue light - they will more accurately reproduce colors under water than the reddish light of ~ 0.8. (R/B) lamps. With 0.37(R/B) being too blue."

So, like esworp said...get a ~6500k "full spectrum" bulb unless you're trying to grow something funny. The Life glo will work well.

I have a pretty good write up about bulbs and spectrum in my signature if you want to check it out.
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Old 06-10-2011, 08:22 PM   #6
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Confused yet? :p
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Old 06-10-2011, 08:25 PM   #7
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Actually..... Kelvin is the unit for color temperature.

What matters to plants is the spectral distribution, which can not be expressed in a single number. It is a curve with peaks in various wave lengths.

Kelvin, in turn, is just a number given by the manufacturer to give us an idea of the expected looks of the bulbs. Sometimes, these numbers coincide with a blue or red hue, but sometimes they don't. Especially for plant grow bulbs, it's just a rather random number. One manufacturer might say one bulb is 2800K, another might label another one with 18000K, and none of that makes much sense or matters to plants.

Pink/purple plant grow bulbs have their peaks in the red and blue parts of the spectrum which is supposed to be optimal for plants. Human eyes are more sensitive in the yellow/green part, so the plant grow bulbs look a bit weird and often dimmer as their "regular" counterparts of the same wattage.

Keep in mind that plants need a certain amount/intensity of light to grow (photosynthesize), and as long as that is given, they are pretty adaptable. If your lighting situation is borderline, choosing some plant grow bulbs should be advantageous.

If the overall light intensity is sufficient, I'd say go by what you like. Some like warmer tones, some like greenish light, others prefer crisp white light. Mixing bulbs can be beneficial for an overall balanced impression. For example, I mix neutral-ish 6500K bulbs with bluish-white 10000K bulbs and pink plant grow bulbs. I would not like one of them on their own, but as a result of the mix the tanks look nice to me.
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Old 06-10-2011, 09:33 PM   #8
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Well...From what I have researched about Kelvin rating in bulbs, is that they are a generic measuring tool. One particular manufacturer's 6500K does not necessarily equal another manufacturer's 6500K to the human eye. Plants actually absorb very little light from the green area of the spectrum. There are a number of different chlorophyll pigment molecules that react to light for photosynthesis. The most predominant type of chlorophyll in most plants REFLECTS green light (hence why most plants appear green), and ABSORB light in the red and blue wavelengths generally. That is why most plant growing bulbs that advertise their spectrum analysis have sharp peaks in the blue and red, but valleys in the green and yellow areas of the spectrum. Red hue plants tend to REFLECT red light waves.
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Old 06-10-2011, 10:28 PM   #9
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Quote:
Originally Posted by bpb View Post
Plants actually absorb very little light from the green area of the spectrum. There are a number of different chlorophyll pigment molecules that react to light for photosynthesis. The most predominant type of chlorophyll in most plants REFLECTS green light (hence why most plants appear green), and ABSORB light in the red and blue wavelengths generally. That is why most plant growing bulbs that advertise their spectrum analysis have sharp peaks in the blue and red, but valleys in the green and yellow areas of the spectrum. Red hue plants tend to REFLECT red light waves.
There is a lot of mis-information about this. Most of this information comes from a study done on algae by McCree 1973 which he later proved was incorrect for higher aquatic plants. From the chart below you can see aquatic plants use light from the entire spectrum with green/yellow only being slightly less efficient than blue/red light.



Quantum Response is the amount of O2 produced(a by-product of photosynthesis) by the plant at each wavelength

For aquatic plants you need to take into account that red light doesn't penetrate water to any great depth(50% of its intensity is lost in 1 ft, and 70% of its intensity is lost after only 2 ft.) Only the shorter wavelengths like blue/green make it down to significant depths and reach most plants. This prompted the ADA to say, "under water plants primarily use the blue part of the spectrum of light." (The wavelength of light and photosynthesis in plants, ADA)



Will the addition of red light hurt...absolutely not. But you don't have to find bulbs that are high in the red spectrum to grow plants. It will probably only make you tank look darker and reddish.

Red plants are red because of a flavonoid made by the leaves to protect it from UV light.
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Last edited by BlueJack; 06-11-2011 at 01:06 AM..
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Old 06-10-2011, 10:33 PM   #10
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Just checked out your writeup right after I posted. It was a very good read with alot of good information. It makes sense that blue light would refract less in water since it has a much higher energy wavelength, whereas red, even if important photosynthetically, will weaken substantially when it hits deep water because of the weak wavelength.
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Old 06-10-2011, 10:43 PM   #11
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Quote:
Originally Posted by bpb View Post
Just checked out your writeup right after I posted. It was a very good read with alot of good information. It makes sense that blue light would refract less in water since it has a much higher energy wavelength, whereas red, even if important photosynthetically, will weaken substantially when it hits deep water because of the weak wavelength.
Fun fact: when diving below 60ish feet, where zero red light fromthe sun has penetrated, unlucky divers who cut themselves will appear to bleed green. ask me how I know this. :]
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Old 06-15-2011, 05:26 PM   #12
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Thanks for all the replies!! There's a lot of useful info here!!! I still have the flora glo 2800 and life glo 6700k set up. I spent about $60 on the plants, so I'm tapped out on spending for the tank this month. I wasn't sure how they'd do with the 2800k but I'm happily surprized....the plants are doing great!!! I've seen so much growth already, so something must be right because they are doing really well!!!!!!!! I think when I get the extra time and money, I will eventually swicth out the 2800k for another day bulb...but so far so good!!!
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Old 06-15-2011, 08:26 PM   #13
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I've used two T12 lamps to light my low light tanks and one was warm white and the other was daylight. ~2800 K & ~6500 K. Plants grew great and was less expensive than GroLux bulbs. Looked better too.

Now I'm just using 6500 K T5HO lighting on my higher light tank.
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Old 06-15-2011, 09:31 PM   #14
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If you find out you don't quite have enough light and absolutely can't add more intensity, you can start injecting co2 and that will allow the plants to better utilize the light they have access to. Courtesy of the tropica report that has been floating around... Good read!
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Old 06-16-2011, 07:18 PM   #15
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what does the new tank look like?...post some pics.
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