# Optimal color temperatures



## Option (Oct 2, 2010)

Hey everyone, 

Not new to the plantedtank hobby but very new to the specifics of lighting. Looking through all the choices of bulbs available these days -- I was wondering what is the best color temperature for plants?

Each bulb seems to burn at a different color temperature, but what color temp range seems to be the best for our aquatic plants?

I'm sure this question has been asked a billion (no, trillon) times already. And I appologize.


----------



## onekraz3 (May 24, 2012)

Yes it have been asked a trillion time 6700k is usaully what alot of people have. 10k to bring out color


----------



## BBradbury (Nov 8, 2010)

*Lighting Color*



Option said:


> Hey everyone,
> 
> Not new to the plantedtank hobby but very new to the specifics of lighting. Looking through all the choices of bulbs available these days -- I was wondering what is the best color temperature for plants?
> 
> ...


Hello Op...

Bulbs in the 6500K range come closest to natural daylight at 5500K. The light blue color of this type bulb is recommended for planted tanks.

I have a two bulb set up on my tanks. The bulbs are T5s. One is a 10000K and the other is 6500K. This combination seems to work well for my low to moderate light plants.

B


----------



## NWA-Planted (Aug 27, 2011)

I originally ran 6500 & 10k, but wasn't getting the colors out of some of my plants so I went to the geisman, aquaflora (pink type bulb) and 6500, results? The reds in my plants came out big time. My aromatica turned a nice pink/purple underneath etc. The best would be a combo of the pink bulb 6500 and 10k, cover all the spectrum 



Sent from a dark corner in my happy place


----------



## temple2101 (Jun 6, 2012)

NWA-Planted said:


> I originally ran 6500 & 10k, but wasn't getting the colors out of some of my plants so I went to the geisman, aquaflora (pink type bulb) and 6500, results? The reds in my plants came out big time. My aromatica turned a nice pink/purple underneath etc. The best would be a combo of the pink bulb 6500 and 10k, cover all the spectrum
> 
> 
> 
> Sent from a dark corner in my happy place


+1. I recently switched to a dual T5HO fixture with a 6500k bulb and a flora bulb (pink). The colors really pop and the growth has been great. Previously I was running a 7000k/10000k Finnex Ray 2. Great light, but nowhere near the coloring out of my plants as my current fixture.


----------



## mach_six (Sep 12, 2005)

5000 to 6500 range is good.

The Gieseman Aquaflora and Midday combo would be good.


----------



## 5BodyBlade (Feb 8, 2011)

I agree. I run a 6500 and a 5000 and I find I get the best plant colors from that combination. I find the 10000 washes out colors too much. I still don't quite get it though. Is the bulb K just for looks or will one provide better growth? Isn't the the entire color spectrum in every beam of light?


----------



## Steve001 (Feb 26, 2011)

Option said:


> Hey everyone,
> 
> Not new to the plantedtank hobby but very new to the specifics of lighting. Looking through all the choices of bulbs available these days -- I was wondering what is the best color temperature for plants?
> 
> ...


Color temp by itself should not be taken alone. A combo of color temp and color rendering index (CRI) will give you a good idea how objects will look. For the most natural rendition of color a light source with a CRI of 91 or higher coupled with a Kelvin temperature of 5500 will create a light that closely matches sunlight at noon. I web search will bare this out.


----------



## Hoppy (Dec 24, 2005)

5BodyBlade said:


> I agree. I run a 6500 and a 5000 and I find I get the best plant colors from that combination. I find the 10000 washes out colors too much. I still don't quite get it though. Is the bulb K just for looks or will one provide better growth? Isn't the the entire color spectrum in every beam of light?


Fluorescent bulbs emit light as a series of peaks and valleys in the spectrum. This is because of how the bulb works - the electric discharge down the middle of the bulb produces ultra violet light, which strikes a phosphor coating on the inside surface of the bulb, and that causes the coating to emit visible light with a spectrum unique to the different phosphors used in the coating. Expensive bulbs contain a mix of different phosphors, selected to give whatever spectrum the manufacturer wants the bulb to produce. Really cheap bulbs use one or two phosphors which produce just a couple of big spikes in their spectrum. So, no the entire spectrum isn't in every beam of fluorescent light.

Color temperature, as used in describing a fluorescent bulb, isn't a well defined parameter, so manufacturers can pick a number and say that is the color temperature of their particular bulb. That means two different manufacturer's 10,000K bulbs can produce widely different spectrums.


----------



## i4x4nMore (Mar 31, 2008)

Somewhere along the line, the companies that market fluorescent bulbs hopped on the 6500K bandwagon, pushing these bulbs as "full spectrum" or "daylight". When it comes to fluorescent, they are neither full spectrum nor even remotely close to the spectrum of daylight.

The light from a metal halide bulb at 6500K will look much different than light from a fluorescent bulb of the same correlated color temperature. True color temperatures only apply to black body radiators: the sun, an incandescent bulb, a metal halide bulb, a stove burner, burning coal or wood, lava, etc. When it comes to fluorescence, as Hoppy pointed out, the manufacturers come up with a "correlated" color temperature that attempts to describe how the bulb's color compares to a black body radiator. But, at the end of the day, you can not make up for wavelengths that are not present in the emitted light. 

I agree with Steve001: Combining high color rendition index (CRI) with correlated color temperature would be a better way to get a nicer looking light to show off the true colors of things. For example, a metal halide of 4100K and 98 CRI looks amazingly like warm sunlight... and it has fooled me many times. No fluorescent bulb that I've ever seen has been able to do that. Good fluorescent bulbs typically have a 85CRI; Cheap ones have about 60CRI. I have seen a few in the 90's, but these are never made in common sizes that fit most fixtures, and are hard to find. 

However, for the plants, it's largely said that they don't care what the color temperature is. They make use of all visible wavelengths to photosynthesize; some wavelengths are absorbed more efficiently than others depending on the photo receptor in question. And from my own anecdotal experience, I've never seen a big growth difference between using incandescent, metal halide, or fluorescent. 

This is probably a good fluorescent bulb: *SYLVANIA, TL-D36W/965, 47.5 in., 36 Watt, T8, 6500K, 900 Series Phosphors, 95 CRI*
Great if you're running T8 with a 48" fixture; Not so great if you're not.


-Jeremy


----------



## Diana (Jan 14, 2010)

Research PAR, the measure of how much photosynthetic wave lengths that are produced by the bulbs. 
Plants tend to use colors in 2 major peaks, one in the reds and one in the blues. A bulb specific to plants will have those 2 peaks and will look pink or purple to us. 
Plants have other coloring materials that are somewhat photosynthetic, and can use most of the visible spectrum, so using several bulbs with different colors, or a high quality bulb that has several colors is fine.
We see the yellows and greens best, so a bulb for plants that has most of its color in the reds and blues is not the best for our eyes. The plant bulb looks somewhat dim, and some fish colors look weird. Using a combination of bulbs, some chosen for the plants and some chosen for our eyes will make the tank look more natural and still grow the plants. 

The K value is more like what the bulb looks like to us and says nothing about what wavelengths it produces. However, many home and office bulbs are rated that way, so finding some way of using the K value is helpful. 
Generally 6,500K or so does seem to grow plants reasonably well. 

I use a mix of bulbs, one plant specific bulb and one chosen from 'Daylight', 'Cool White' or similar. To me that makes the tank look right. 

To get the best results from any bulb use a high quality reflector.


----------



## Option (Oct 2, 2010)

Wow thanks everyone. That certainly is alot to swallow! 

Anyhow, my current light housing only takes a max of 13W....so what bulb would you recommend me to give optimal grown of my plants?

(yes, I will eventually get a different light housing)


----------



## Steve001 (Feb 26, 2011)

i4x4nMore said:


> This is probably a good fluorescent bulb: *SYLVANIA, TL-D36W/965, 47.5 in., 36 Watt, T8, 6500K, 900 Series Phosphors, 95 CRI*
> Great if you're running T8 with a 48" fixture; Not so great if you're not.
> 
> 
> -Jeremy


I looked for a spectral distribution chart for the above light, but could not find one yet.

I've seen fluorescent bulbs listed having a CRI of 98. But that is misleading. It's misleading because sunlight no matter whether it's predawn light, twilight and everything in between it always has a CRI of 100. It's relatively easy for bulbs makers to match sunlight near the beginning or end of day. That requires few phosphors. Not so easy to match the output during the day.


----------



## Hoppy (Dec 24, 2005)

I have read that CRI for incandescent bulbs is always 100 also, and that CRI isn't of much use for aquarium lighting anyway. I tend to agree with that, and never consider CRI when I think about planted tank lighting.

I believe our goals are to provide appropriate light for the plants to grow, light that will let the non-green plant colors show up well, and light that makes the various colors in our fish look good. I don't think that requires a high CRI.


----------

