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Discussion Starter · #1 ·
hey all,
I'm just wondering if I need to get different lighting. Right now I'm using 2 13W CF bulbs that have a color temp. of 2670K. I know that 5500K is the closest spectrum to natural sunlight, but do I need to change my bulbs to something that's around 5500K or can I keep using the ones that I am using now?
 

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The lowest I ever used was around 4000k. The light did an okay job at growing my plants. But once I bumped it up to 6500k I noticed a growth difference, not to mention the plants just looked better under this spectrum.

Are you using the screw in variety? If so, it shouldn't be too hard to walk over to walmart and pick up some 6500k bulbs. In my opinion, anything under 4000k doesn't look good, and doesn't grow plants well. I don't know the exact science why that is, but it is what it is. ;)

-John N.
 

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Lighting for a planted tank should not be chosen on color temp alone. It is true that 'full spectrum' bulbs are referred to as bulbs between 5000 Kelvin (K) and 6500 K and are best for planted tanks. Yet this does not indicate what type of light (wavelength in nanometers) the bulb is actually emitting. If you want both good leaf development/growth (blue light) and stem elongation (red light), you need light in both the blue and red spectra for photosynthesis.

You need a mix of blue and red for your plants, and green for you (brightness as perceived by humans). If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum. Do not equate this with good lighting for your plants, because plants don't use light in the green spectrum for photosynthesis.

For green plants the lighting peaks that are most important:
chlorophyll-a: 430nm/662nm
chlorophyll-b: 453nm/642nm
carotenoids: 449nm/475nm
Red pigmented plants use more light in the blue area of the spectrum.

Beyond choosing lighting that is optimal for photosynthesis, as above, you should choose lighting with the color temperature that best suits the aesthetic goals of your tank. So, don't obsess about color temperature beyond how you want your tank to look. From a color temperature standpoint, blue-colored light will enhance blues in your fish. Green-colored light will make the tank look bright to humans and enhance the green color of your plants. Red-colored light will enhance the reds in your fish, and any red plants. If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum.

I have attached some jpg's to help understand lighting and how plants react to it. I have found it best to provide a mix of lighting to a planted tank. The GroLux bulb is perhaps the best plant bulb available but it has very little green light so the visual effects of your tank will look dim and purplish. Yet if you add some other lighting such as a Philips 6500K the effect is more pleasing to the eye and still beneficial to the plants.
 
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Discussion Starter · #5 ·
wow, thanks a lot for the info newt. I've never really thought of the aesthetic part of the lighting until I changed my bulbs recently. I liked the 2760K a lotbetter than the 6700K, but it wasn't as beneficial for my plants. What about mixing the two bulbs, what temperature would my lighting be rated at or would it still remain the same?
 

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I just scanned some new graphs that may help understand more:
 

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I use a 40 watt grolux standard and a 40 watt grolux wide spectrum (both linear fluorescent) and (2) 55 watt Philips PL-L 950 CF. The Grolux standard has no kelvin rating. The wide spectrum is 3400K and 89 CRI. The Philips CF are 5000K and 91 CRI. Nanometers as displayed on attached spectral graphs:
 

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Seems this site doesnt like the size of my pdf file for the grolux graphs. I will see if I can reduce it.
 

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Anyone use 10,000K? I saw the comparison pics for the 9325K and 6700K and plants do have more green with the 6700K, but the reds and orange look great under 9325K. Anyone running 10K and how is it?

Thanks
 

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Nice topic! Two quick items:

(1) The previously posted color-temperature-plant-pigment graph is very, very useful! Everyone should keep a copy of this. http://www.aquaticplantcentral.com/...r-temperature-plant-pigments.gif?d=1149132070

(2) The Kelvins number for flurescent tubes, by itself, is almost too much of an approximation to be useful. The number is supposed to represent radiation discharge from a heated object. If this was the case, it would have some sort bell shaped curve where the peak occured at the associated light wavelength for that temperature. Due to the laws of physics of how fluorescent tubes work, phosphor atoms lining the glass tube release photons at very specific frequencies, which do not at all generate a smooth curve one should expect with a Kelvins number. Different phosphors have different spectral emission patterns.

Application
Each manufacturer/model tube is different. It's Kelvins number just means that there is a strong emission line at that frequency. Get the emission chart for that tube. Compare your tube's chart against the color-temperature-plant-pigment graph. Tube emission peaks not in the plant graph are ignored by your plants. The more the tube phosphors emission peaks conform to the plant graph, the more useful the tube is to your plant.

Examples
Q: So are true actinic bulbs beneficial for planted tanks or not?

A: Let's look at the chart. 420 is where the peak starts to rise for several values. This means that there will be some useful light, but it won't be optimal. (Kinda makes sense since Actinic is optimized for marine corals and not plants in general.) Another tube selection will provide much more benefit. With the cost of actinic tubes, it's probably a waste of money for a plant tank unless you want to show off some of those new glowlight anios.

Q: 420nm is near but not inside any of those ranges you (Nate's earlier post) gave for essential plant functions.

A: Let's do a sanity check on those numbers and what they mean against the chart:
For green plants the lighting peaks that are most important:
chlorophyll-a: 430nm/662nm
chlorophyll-b: 453nm/642nm
carotenoids: 449nm/475nm
The above numbers do identify the peaks. Therefore, same conclusion as before.

Q: What about 10,000K?

A: Each model of a 10,000K tube has a different emission spectrum. Obtain the spectrum chart for the particular manufactured bulb and see how the peaks line up to get your answer.
 

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I believe that a bulbs kelvin color temp is determined by the color the tube appears to be (what color the bulb is) not any of the emissions through the visible spectrum it emits.
 

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allaboutplants said:
Anyone use 10,000K? I saw the comparison pics for the 9325K and 6700K and plants do have more green with the 6700K, but the reds and orange look great under 9325K. Anyone running 10K and how is it?

Thanks
You guys got a great discussion going on here. Great job Newt in explaining things graphically and verbally. I'll leave the "meat" alone, but I'll just answer this quick question. I'm running a GE 9325K with a 10000k bulb. In terms of looks, it balances out the pink hue, and also appears very white. It's different, and I like it. In terms of plant benefits. The plants couldn't be happier, growing rapidly and pearling daily.

-John N.
 

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Thanks, John N.

The GE 9325 bulb is an enigma of sorts. The bulb will look pink, yet it has a blue hue to it when shining into water. It only has a 67 CRI. A lot of people like it. I used them for awhile but have switched to Philips PL-L 950s, a whiter light with a 91 CRI and less $$$$$.

Attached is the spectral output for the GE 9325K. You will notice that the graph is depicted in relative power. This means compared to the highest spectral peak = 100% and everything else is, well, relative.

The 6700K bulb is probably a Coralife bulb and they have a huge green spike. See attachment for this bulb.
 

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Newt said:
I believe that a bulbs kelvin color temp is determined by the color the tube appears to be (what color the bulb is) not any of the emissions through the visible spectrum it emits.
You may wish to rephrase that, I think this was a typo on your part though. (Your phrasing runs counter to the fact that a bulb appears to be a color becasue it emits light, which happens to be photons with colors that correspond to all the emission lines demonstrated in its spectral chart.) :)

We don't see the spikes without a prism/diffraction grating because the perceived color of the tube is a result of how the human brain processes (color balancing and averaging) the information after the eye senses it (with red, blue and green receptors). So, when you look at the spectral chart of a bulb and group the red, green and blue spikes together you can get an idea of how the brain will color balance and average them.

Different spectral emission patterns can produce very similarly colored bulbs though.
 

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ya what about the 10,000K bulbs which is better 6500K or 10,000K because those seem to be the standard
 

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Depends on what you want your tank to look like. The 10000K will have a more bluish hue to the human eye. It will also have less red emissions emitted (visible spectrum) which help with stem elongation. A lot of people like the 10000K for planted tanks as the blue emissions stimulate photosynthesis.
 
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10,000K gives a really bright, intense look. That is favorable for some designs. It also works well with certain colors of fish.
 

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So has anyone tried an 8000K bulb? I know ADA makes them but I don't have that much cash laying around (i.e. I'd have to buy a totally new fixture because of the pin arrangement. Stupid competing standards), but I found out that All Glass makes an 8000K 55/65W bulb that fits into my Coralife fixture. I've heard 8000K is "optimal" and if ADA uses it there has to be some benefit, even if it is just in viewing the tank.

Here's a link to the Coralife bulb and light output graph (looks like it lines up with the earlier mentioned wavelengths needed for plants):

http://www.all-glass.com/products/lighting/lighting.html

Oh and, anyone know what 55/65W means? How is it both?
 
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