For those of you that which to understand what Kelvin is look at the color chart here:
Color temperature - Wikipedia, the free encyclopedia
The interesting part is the black curve and the markings on it. Look for example at 10000K. Now you can follow the markings up and down and now you will see that a 10000K rated bulb can be anything from greenish to white to purple.
Thus. A higher K-rating does not equal to more blue color, even if the aquarium equipment providers think so. Their Kelvin-ratings are very probably just a number some marketing guy have come up with out of thin air - "ah, this is a blue bulb it has to be very high kelvin!".
Regarding attenuation of colors in water the attenuation effect in our extremely shallow waters in our aquariums is next to nothing. The effect will not be seen until a couple of meters of water column.
Regarding what bulb to pick there is a way to squeeze out as much usable photons from a bulb as possible. But we need to learn that usable photons for humans is kindof the opposite of plants - humans are very sensitive to yellow and green colors, and not so sensitive to blue and red colors.
Lumens for example is a direct measure of human eye sensitivity and it looks like this:
But plants are unsensitive to green (obviosly since they are reflecting green!) and have a sensitivity looking something like this:
So. What you are looking for is a bulb that spends as little effort on producing yellow-green light and as much effort on producing blue and red.
That makes ordinary light bulbs a bad choice - they do not only produce alot of yellow-green light, they also waste much of their energy on producing heat.
So to make the most intelligent choice of bulbs you can take a peek at it's spectral distribution and see if it has alot of blue and red, and as little green-yellow as possible!
Last edited by PlantedFishGeek; 09-25-2008 at 02:01 PM.
I think someone over att APC actually ran a planted tank with actinics, don't know for how long. You should see plant pearl, but the growth might be somewhat wierd.So atintic would work well considering it is heavy blue spectrum?
Actually 6500K is about the very neutral color of light on a cloudy day so it should contain equal amount of all frequencies.and it seems 6500k is the highest in red and blue light so that explains the moss turn around under the 6500k bulb!
Flourescents can't produce an even spectral distribution like the sun light, but it can mimick it by emitting tre distinct colors in equal amount, Red Green Blue. Like your monitor or TV.
6500K bulbs are average or a little above average regarding growth rates though. Tri phosphor bulbs like Aquarelle, Aquastar, PowerGlo, Triton etc emits *very* much energy in the blue and red parts of the spectrum. Don't get scared of their 10000K rating, as you have learnt it doesn't tell anything about the actual color or the spectral distribution.
While I wouldn't dispute the findings that led to the data provided on the chart, I would question the practical application. Isn't it odd for example how the highest point in that chart is at about 420nm which happens to be the peak frequency of the actinic bulb? It makes me wonder whether this chart was produced from data from a marine algae. Based on the data alone the best course of action would be to use 100% actinic but of course that would be ridiculous.
The chart shows relative photosynthetic rates but it does not address adaptability or intensity. If a plant is grown under a certain spectral curve and then suddenly exposed to a different curve I would expect a drop in photosynthesis while the plant rearranges it's pigmentation to adjust to the new spectrum. It also clearly shows that photosynthesis under green/yellow light is non-zero so that means photosynthesis can and does occur under green and yellow light.
So how well does a plant do if grown under common office/household type spectrum? Well, here's how:
This is A reinikii (supposedly a difficult plant) and P. stelleta grown under the T5 version of common household/office building type bulb (Osram 840) in the yellow/green range. The advantage? They are 3X-5X cheaper. The result? They grow just fine. The disadvantage? The yellow cast of the tank is garish an absolutely awful. Everything looks like hamster vomit. You can see that the Althernathera which is supposed to be a red plant has a sickly orange color under these lights while the green stelleta behind doesn't look too bad.
I finally got fed up at having to look at the revolting color cast and replaced some of the bulbs with other bulb types. The plants carried on as normal and I didn't see any growth rate differences although I didn't specifically measure it.
So this shows that we don't have to pay megabucks for special designer bulbs and that we don't have to worry about Kelvin values except if that particular bulb happens to give your tank a color cast that you particularly like and can't achieve with alternative bulbs. Common household bulbs do just as good a job as any regardless of their spectral curves. You only ever have to worry about what looks good to you. If you like to mix the blue cast of actinic with some other color then go for it. If you like the red cast of Grolux type bulbs then fine. I don't have any trouble growing plants with whatever bulb type used. Each bulb gets just as hot as the next and the plants grow just as well regardless of published spectral curve. There are a lot more things that affect plant growth than spectral quality of one's bulbs. It's not even remotely close. CO2, nutrient dosing, maintenance and flow/distribution are orders of magnitude higher in importance than any spectral characteristic of some bulb.
Plants can easily grow as well even if they are raised in perfectly green light. They will simply develop pigmentation to convert the green light and to pass it's energy onto the chlorophyll. Again, I'll go back to the rain forest canopy example. What color light filters down to the plants living on the forest floor under a canopy of green? These plants only ever see green and a little yellow light and they grow perfectly fine. The intensity and therefore the photon flux density is much lower under the canopy which limits their growth rate, but that's about it.
Can anyone tell me if Aquatic plants can suffer Nitrogen burn if the nitrates in the tank get to high?I know land plants can be burned was wondering if it was the same in our tanks?
From my experience and from what I've read elsewhere it really matters little. Any difference is probably so minute as to be over-shadowed by more important things like photo-period and ferts.
Worrying about K ratings with a planted tank is like worrying about a tiny scratch on a car when the engine is not running. I guess if someone was up to such a standard of perfection with their plants that everything else was working and running perfectly, it would be time to worry about K ratings. I'm not there yet. But then I guess K ratings wouldn't matter, because the tank would already be near perfect. It's interesting to learn about, but not much practical value for the majority of people.
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