[Wet Thumb Forum]-confused on lighting. K vs Spectrum

[imported_chinaboy1021]

im confused on which bulb i should get for my 20 gallon. ive read too many times that plants "use" 5000-6500K. but GE 9325Ks are good because its high in both the red and blue spectrum, which plants use most.

so i dont know if i should get a 5500K zoomeds, or 18000K aqua-glo.

[imported_chinaboy1021]

im confused on which bulb i should get for my 20 gallon. ive read too many times that plants "use" 5000-6500K. but GE 9325Ks are good because its high in both the red and blue spectrum, which plants use most.

so i dont know if i should get a 5500K zoomeds, or 18000K aqua-glo.

[gpodio]

Personally I feel it's mostly a matter of taste from say 4800K to 10000K, at least that's the range of light I've used and have seen little difference in plant growth. 18000K on the other hand may be a little too high but I've never tried it before so can't really say. IMO, the lower K bulbs display reds better and the greens have a yellowish tint to them. The higher K bulbs on the other hand show off the greens much better IMO but wash out the reds a lot. There are exceptions such as the All-glass tubes which claim to be in the 9000K range however they seemed to have a lot of red in them to my eyes. I prefer using a lower K bulb in the back and a higher K bulb in the front where the small bright green plants are such as glosso and riccia.

Although it's not the best example because the plants were trimed and moved around a lot and the All-Glass tubes are somewhat different than similar bulbs in the same K range, but here are two pictures of the same tank under two different lights. The first is using a mixture of Trichromatics 6700K and 10000K, the second were the All-Glass tubes which claim to be a higher K but have a lot more red in their spectrum.





Hope that helps
Giancarlo Podio

[Roger Miller]

Aquarium lights have two purposes; they grow plants and they let us see the plants.

I use the CRI value as the best overall measure of a tube quality. It is a fairly direct measure of how good the plants will look under the lights. Tubes with high CRI ratings give more natural-looking colors.

In order for a tube to rate a high CRI value the light it produces must contain a balanced amount of red, green and blue light. That balance guarantees that a lamp with high CRI will also grow plants. It also means that the healthy plants and fish will look healthy and that colors will be true and natural.

K is a relatively useless number. It tells you whether the tube's output spectrum is weighted to the reddish or the bluish wavelengths. That doesn't always translate into the light looking reddish or bluish. It doesn't tell you that the light can grow plants well and it doesn't tell you whether the light will produce colors that are balanced and natural.

I think the best way to select lights is to first find a lamp with a high CRI -- 90 or over is best -- and then check to see if the color temperature fits your taste. A high CRI lamp with a color temperature near 5000 should be about the same color as direct sunlight on a clear, sunny day. A high CRI lamp with a color temperature nearer 7000 K might look more like light on a hazy or cloudy day. If I remember right, light from a clear north sky (in the northern hemishere) has a color temperature of something like 12,000 K,but I could be wrong on that.


Roger Miller

"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein

[gsmollin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by chinaboy1021:
im confused on which bulb i should get for my 20 gallon. ive read too many times that plants "use" 5000-6500K. but GE 9325Ks are good because its high in both the red and blue spectrum, which plants use most.

so i dont know if i should get a 5500K zoomeds, or 18000K aqua-glo.<HR></BLOCKQUOTE>

Plants do "use" 5000-6500 K, because that's the temperature of the sun, depending on your latitude. It is around 5500 K in the tropics. However, the sun is a black-body radiator, which means it has a normal distribution of radiation, with a peak at a wavelenght (yellow) of light corrsponding to a hot body radiating at 5500 K. No fluorescent tube has that characterisitic. They all radiate from phosphors, which have "line" spectrums. To get white light, a tri-phosphor bulb uses, say, red, green, and blue phosphors. The difference from one tube to the next is in the phosphorescence of those phosphors. This all make "Kelvin" ratings a lot of bupcus.

You should really pick tubes that make your aquarium look good to your eye. Get enough of them over the water to make the plants grow. Then you will be happy.