K rating on bulbs and Plants.

Both tanks have 2 watts per gallon, but the ten gallon effectively has considerably less, because for small tanks the lights are not as efficient. It isn't clear to me why that would be true, but it is. One possible partial reason is that the smaller the bulb the smaller the percentage of the bulb surface is actually producing light. So, your 10 gallon tank almost certainly has a lower light intensity than the 55 gallon tank.

 

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!

 

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.

Actually 6500K is about the very neutral color of light on a cloudy day so it should contain equal amount of all frequencies.

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.

 

Hi defdac
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.

Cheers,

 

I have used everything from 4000k PC bulbs to 6700k and 10,000k PC bulbs and now use 1 - 18,000k T5 (Hagen Power-Glo) with 2 - 6700k T5's (Hagen Life-Glo)over my 72 gal. My 10 gal has 2 - 18,000k T8 (Hagen Aqua-Glo) bulbs going. Plants grow fine in all. Except for the 4000k bulbs (which were quite yellow-warm) I barely see any difference in the light temp to my eyes viewed on the plants, though the 18,000 bulbs do look pinker than the 6700k bulbs when looking directly at the lit bulbs and side by side.

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.

 

A very interesting discussion! I have learned something, and some days go by when I can't say that.

 

Hi Hoppy,
If you still have that PAR meter I would love to see the results of a comparison of Photon flux readings between an actinic, a "daylight", a tube from Homebase and a Grolux type tube of similar wattage and configuration.

Cheers,

 

It's most probably taken from an Elodea species. It's the most common plant to use when experimenting with photosynthesis.

Here you have the action spectrum for Zooxanthellae, Figure 7: Advanced Aquarist's Online Magazine - Feature Article: Coral Coloration - Part 7: Coral Reflectance, Chromoproteins and Environmental Factors Affecting Non-fluorescent Pigmentation

Why would you not want to use the red end of the sensitivity?

That is not true at all. Drive a tank with 6500K bulbs and change them to Aquarelle/Aquastar/Triton and watch the photosynthesis explode.

I have and many others.

That is ofcourse not a valid point if you want to maximize growth with minimum electricity input.

There is a gap between "be able to use" and "prefer", and that you can use when selecting bulbs.

The 840 is one of the bulbs with the highest PUR-efficiency of them all, despite it's yellow cast. =)

Fail.

If you don't have the space for more bulbs and have a limited electricty budget, or just want to be smart energy wise then you would want to look into things that squeeze every tiny USABLE photon out of your system.

First thing is to select the best reflectors, then use electronic ballast and lastly use a bulb that produces the most USABLE radiation for the electricity spent.

Yes, why don't you use the old filmant bulbs then? =)

 

It boils down a bit to what you prefer. You can drive a big block American muscle car around a track and spend endlessly more money on gas and get beaten by a Lotus Exige that use a fragment of the gasoline.

With the big block you get a nice sound and you travel fast on straights and you will reach goal, but also spend more money on gasoline and spit out more CO2.

The Exige is more efficient, I would almost say more intelligent.

 

It depends. If it is an ordinary 10K tri-phosphor bulb like Triton/Aquastar etc they often only loose about 10-15% of their initial intensity, until it drops sharp at the end of their life. Those bulbs can be used until they fail - you can see when they are about to fail because they get very dark when they are not lit:



One cool thing: Do a gaussian blur on the lit bulbs picture, desaturate it and look at the relative RGB-values between the old and new lamp. You will se about 10% difference =)

This does *not* apply to all kinds of phosphors. GroLux-bulbs for example often uses a completely different (and innefficient) phosphor mix that drops the intensity much more than 10%.

And there you have another variable to thrown into the mix - different phosphors will give different efficiency turning electricity (plasma) to light, and that is also reflected by the PUR-efficiency....

 

Does this mean that 6500K bulbs, those marked that way and intended for ordinary household use, are poor choices for an aquarium? I am thinking of the spiral screw-in CFL bulbs in particular, knowing that they aren't good aquarium bulbs anyway. Is it just this color bulb that is a poor choice, or are all ordinary household use bulbs poor at growing plants?

 

No the K-rating doesn't say anything really. Almost not even the color.

Garage or kitchen bulbs are seldom very efficient, but they can be. 840 is a good example. Ugly color though.

The spiral 6500K bulbs I've calculated PUR for have been average. Like GroLux or 965 for example. Ordinary screw in spiral "economy" bulbs with yellowish tint have been under average, almost like Halogen/filament bulbs. And that is rather poor efficiency.

I'm running Aquarelle+Deltec Midday now, but will exchange both to 2xPhilips 965. I have enough wattage and good reflectors so I don't have to be too anal about the spectral choice and can focus entirely on what I think looks the best.

When i ran a 310 litres tank it was much harder to get enough light (I couldn't use any good reflectors) so then the PUR-efficiency actually made a dfference.

 

Hi thought I would jump in
I also am learning about the bulbs. I do love this site but it can twist my brain (good thing). Hope I make sense below.
If a tank 12" to 18" deep uses say a 10000k @ 42w This light would not be the same in a 24'' tall tank. I know the leaves process the light to energy. But what about the plants at the substrate level? I have Fissiden next to the substrate my 24" 45g. It grows really slow under the above bulbs. I changed to 6700k 96w and besides a lot more green spot the fissiden has slowed growth. If K is for color why does wattage effect the plants more? My new light so far has increased my GSA and growth and color are good except on the Fissiden and Subwassertang (near the gavel). So these changes have to do with the depth the light can reach also (right?) All the GSA that has increased is in the upper half of the tank. I hardly have any GSA in the lower half. Its been two weeks with the new bulb and the GSA is staying about the same size. Man that stuff grows back fast after you scrape it.
If a high light tank requires the CO2 and we wish to use lower light, which is best? Do we stay in the upper range of 2wpg or go for the less? As I said wouldn't this also be different for the height of the tank? My goal is Low watts, EI with excel. I like the 10000k color. But don't mind the 6700k