K temperature Question

DAVIDFBT

DAVIDFBT

Extinct? Since when?
Feb 3, 2008
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Great Lakes, Illinois
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Today, I went to buy a new light for my tank because I have been getting tired of looking at yellow lights over my tank all the time. I found a light that said 7800K and I thought to myself, that's not too far away from 6700K, I'll buy it. When I plugged it in, the light looked extremely purple, way more than 7800K. I have another 6700K light over my tank and it looks like a blue white type of light, while the supposedly 7800K light looks nothing close to 6700K. Is my new light really 7800K? I currently have two T8 24" lights (17 watts each), 1 4200K and the other the 7800K light along with a 36" T12 (30 watts) 6700K light over my 30 gallon tank. Will the purple light affect my plant growth?
 
Once my quantum meter arrives I plan to test this out for myself, but talking with Tom Barr the other day, he said color temperature has little to do with plant growth, and it's more about, well, really the PAR, but slightly easier(but not as accurate) the wattage. The color temp is really about how we view the tank.

Additionally, it's possible the bulb could be manufactured with a different component material inside the bulb similar to the GE 9325.

Either way, it will not affect plant growth. As long as you like how it looks, keep using it.
 
Good, I thought that they where so purple that they would not help in growing plants. I really like the new light though, it makes the colors of my fish pop out alot more.
 
jmhart said:
Once my quantum meter arrives I plan to test this out for myself, but talking with Tom Barr the other day, he said color temperature has little to do with plant growth, and it's more about, well, really the PAR, but slightly easier(but not as accurate) the wattage. The color temp is really about how we view the tank.

Additionally, it's possible the bulb could be manufactured with a different component material inside the bulb similar to the GE 9325.

Either way, it will not affect plant growth. As long as you like how it looks, keep using it.
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From reading Tom Barr's stuff on Kelvin ratings that's what I have heard as well...
 
I've been researching this heavily across the net the past week or so and come to the conclusion that while blues and reds are what cause the pours to open up on the leaves (allow the plant to "breath") a 5000k wide spectrum is the best way to go, giving a primarily "white" light to the human eye, while spiking towards the blue and red kelvin ratings. From my research, I've gathered that while kelvin rating doesn't directly affect growth, it DOES affect plant "respiration" allowing it to make the most use of the present CO2 desolved in the water, which in turn DOES affect growth if CO2 is being added in sufficient amounts, and thus, the overall health of the plant. If you're not using pressurized CO2 then it's not as important IMHO. Sorry I can't cite sources, just too many over the past week or so bringing me to a cumulative conclusion.
 
Wish I could still find the article, but the net result of it was that the "K" rating used is a very incorrect expression. Has more to do with the spectrum spread of visible and non-visible light (to the human eye) and lumens.

Your 5000 rating is close to a sunny day, 7000 blue sky day and 8000+ to an overcast day.
 
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Light color may have a small impact on how your plants grow(short and dense vs tall and sparse), but considering the relatively low-light aquarium plants receive it's not likely you'll notice.
 
I hate being one of those guys that says "But Tom Barr said this.....", so that's why I plant to conduct my own experiments just so I can know for sure and be able to say "I did this and the results were..."

But, Tom has said repeatedly that temperature has nothing to do with plant growth. He said that for many bulbs, the kelvin temperature listed on the package may not be any where near it's actual black body radiation. He said that they tend to just pick a number that will sell well.

Additionaly, every bulb is different, and puts of a differenct spectrum as well as different PAR values, so even comparing two "10,000k" bulbs from different manufactureres is hard.

Hence the quantum meter. Currently I'm using 10,000k bulbs from ahsupply and one of the Coarlife Colormax-6700k PC bulbs. Im partcularly interested to see what the Apogee has to say about the Colormax bulb.


The easiest and cheapest method is to make sure you have enough wattage, and from there pick some bulbs that look good to you.
 
jmhart said:
I hate being one of those guys that says "But Tom Barr said this.....", so that's why I plant to conduct my own experiments just so I can know for sure and be able to say "I did this and the results were..."

But, Tom has said repeatedly that temperature has nothing to do with plant growth. He said that for many bulbs, the kelvin temperature listed on the package may not be any where near it's actual black body radiation. He said that they tend to just pick a number that will sell well.

Additionaly, every bulb is different, and puts of a differenct spectrum as well as different PAR values, so even comparing two "10,000k" bulbs from different manufactureres is hard.

Hence the quantum meter. Currently I'm using 10,000k bulbs from ahsupply and one of the Coarlife Colormax-6700k PC bulbs. Im partcularly interested to see what the Apogee has to say about the Colormax bulb.
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Aquariums recieve INCREDIBLY low-light. Freshwater ones, at least. At minimum, I run the equivalent of having 80watts over a 10g tank for my terrestrial plants. At the upper ends, it's more like 170. Anywhere from 50-100wpsf. I can tell you absolutely *without question* that light colour matters.


Without fail, whether I'm growing catnip, mint, strawberries, whatever, blue light gives me more dense plant growth while orange light spreads it out and provides better fruit development. Tom Barr is absolutely not referring to plants reacting to light color at a cellular level, but rather referring to whether or not you're likely to notice or care in your own aquarium.

Considering pretty much every aquarium is going to be somewhere around 5000k, or up to 6500k, he's probably right. Nobody lights their aquarium with high-pressure sodium security lamps, but I'll be damned if they don't make good strawberries. (Edit2: Continuing upwards through the kelvin scale will simply add more blue light, which beyond a certain point, likely makes no difference. The important change would not be an aquarium lit with 10,000k or 15,000k or 20,000k bulbs, but rather one lit with 2000k)

Edit; It's important to note that I am NOT referring to kelvin as some sort of measure of "total" light. I'm talking about equal PAR hitting the plants, just different spectral distribution.
 
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