Kelvin (k)

[aquariumboy]

Is k important in planted tanks?

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[Coyne]

k stands for potassium, rather than Kelvin, in the context of planted tanks.

Potassium is one of the fertilizers used to grow healthy aquatic plants.

 

[P220]

Kelvin on the other hand, is a lights color temp, and you generally want that at 6500-8000*k for plants. Then you have PAR values, which come onto play for determining low to high light situations

 

[aquariumboy]

Kelvin on the other hand, is a lights color temp, and you generally want that at 6500-8000*k for plants. Then you have PAR values, which come onto play for determining low to high light situations

So which is better on a 20 gallon high tank: one 15 watt 6500k fluorescent tube or 2 x 20 watt 2700k cfl?

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[Brookster123]

So which is better on a 20 gallon high tank: one 15 watt 6500k fluorescent tube or 2 x 20 watt 2700k cfl?

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Neither will grow anything but low light plants..

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[Fishperson]

2700k doesn't sound good. Remember that higher on the kelvin spectrum is blueish lights (10,000+) and lower is more reddish. 7500 is more whiteish and 6000 is reddish. If you want red plants then maybe 6300k would be good. If you want normal plants then 7000-8000.

 

[aquariumboy]

Neither will grow anything but low light plants..

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Will 2 14 watt 2700k be good?

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[aquariumboy]

Will 2 14 watt 2700k be good?

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I meant 5000k not 2700k my bad.

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[Fishperson]

If its 5000k then maybe you have a shot but ideally you want 6000-8000 depending in plant color.

 

[Fishperson]

What size tank is this and what are the dimensions? You really need to specify.

 

[BillD]

5000K is perfectly fine, and in my experience better than 6500K or higher. However, there is more to it than just the kelvin temp. The actual wavelengths of red and blue light available vary from bulb to bulb even from the same manufacturer. A bulb with a high Colour Rendition Index (CRI) is more likely (I believe) to have a good complement of the right colours of light for good plant growth. Keep in mind that the colour temp of sunlight at noon, on the equator, is around 5500K, not 6500K and not 8000K.

 

[Fishperson]

5000K is perfectly fine, and in my experience better than 6500K or higher. However, there is more to it than just the kelvin temp. The actual wavelengths of red and blue light available vary from bulb to bulb even from the same manufacturer. A bulb with a high Colour Rendition Index (CRI) is more likely (I believe) to have a good complement of the right colours of light for good plant growth. Keep in mind that the colour temp of sunlight at noon, on the equator, is around 5500K, not 6500K and not 8000K.

True but I think this is meant for a low light tank. 5000k lights are generally reddish and it may be harder to find low light red plants.

 

[MeCasa]

If you have the capability to use two bulbs use one of each as they both are different spectrum.

If I could only have one I'd go 6500...no competition

When you get some 'extra money' (if there is such a thing) you can invest in Full Spectrum bulbs

 

[BillD]

True but I think this is meant for a low light tank. 5000k lights are generally reddish and it may be harder to find low light red plants.

5000K are not reddish, nor do you need reddish light for red plants. You need high intensity. Red plants that don't get enough light will turn green, or fail altogether. Having used both 5000K for and 6500K for plants, my results were much better with the 5000K, and the plants looked better. I didn't care for the way the green looked under the 6500K. Again, spectrum is the key, not the K temp. As well not all bulbs of the same K temp will give you the same results.

This is a tank of E. latifolius, chain sword, under 5000K. two 32W t8s. The second is Vals in the same tank. The tubes are over 3 yrears old.