6,700K or 10,000K: A little lesson in light temperatures...

[Viciente]

This was asked in another thread in this forum. Because I put a lot of effort into the answer, I thought I would re-post this as its own thread so others can benefit from my answer as well:

<PROFESSOR MODE ON>
Color Temperature is the measurement of color expressed in Kelvin (K). The reason this measurement is called a "temperature" is because it was derived from a theoretical object called a "black body radiator." When the radiator is heated, it changes from black to red to yellow to white to blue. The lower the Kelvin rating, the "warmer" or more yellow the light. The higher the rating, the "cooler" or more blue the light. It does not actually reflect the actual heat temperature of a light. For example, you can have an 18,000K fluorescent lamp which is cool to the touch. Therefore if you are using a light source such as fluorescent lighting, you will probably not affect the physical heat temperature of the water. Now if you use Metal Halide as a light source, you will need to have a decent distance between the tank and the lamp if you do not wish to heat up the tank.

Here is the color temperature spectrum in Kelvin (K):


Freshwater aquatic plants require peaks in the red spectrum for optimal growth, as freshwater aquatic plants' photosynthetic ability is most sensitive to red light.

Coral requires mostly intense blue light, hence the need for actinic lights. Blue light which is produced is generally not used by freshwater plants and therefore should be avoided.

If one were to use a light source which produced peaks in the red and blue spectrums, the overall effect would look quite garish. If one were to use only red light, the fish in the tank would look rather odd. Now we all want our fish and plants to look their best, so to compromise, there are full spectrum lights in several temperature ranges, and depending on the look you would like to go for.

Referencing the color temperature chart above, typical bright sunny days average between 6000K and 7000K. We all agree that clean bright sun is what makes our fish look the nicest, and as a side effect, generally helps us grow healthy plants.

Therefore, as a result the optimum spectrum for an aquarium would be 6,700K as it offers the most realistic lighting for fish, and the necessary red wavelengths for plants to photosynthesize properly. So that color temp is a win win situation.

10,000K light would emulate the light from an overcast day in real life, 18,000K would be closing in on Actinic light, which would not be beneficial to freshwater aquatic plants, so I would avoid such color temperatures in a freshwater tank.

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I hope this information helps you....

[Masta_Cheef]

Sweet, thanks very much for the info.. I think it's sticky worthy.

[zeek]

Originally Posted by Viciente

10,000K light would emulate the light from an overcast day in real life

Would this be the best wavelength to simulate early morning light before the mains kick in?
What about afternoon/dusk? I assume a lower temp would be best for this application?

I want to have three timers;
T5 morning,
morning+MH 6700 daylights+afternoon,
then T5 afternoon.
I also run moonlight LEDs 24/7, because I like the look at night. Plus fish in the wild are rarely subjected to complete darkness.



Isaac

[wayne]

I would also note that while the K scale works quite well till about 15000 K, beyond this it is largely theoretical, and very open to manufacturer interpretation. 20LK bulbs are very variable in appearance, and 50K's unbelievably so.

I would also note that the colour of a bulb has an influence on how long it will retain it's intensity. Bulbs colours are determined by varyingthe amounts of red,yellow and blue colour components. In any bulb the blue components will decay and degrade much faster than the red and yellow. For a white bulb this will appear as slight drop in intensity and a shift to a more yellow colour. For more 'blue' bulbs (higher K) there will appear simply a larger drop in intensity. Some of the higher K metal halide bulbs , especially in the higher wattages will have lost up to 30% of their intensity, and thus require changing out after as little as 90 days.

[Viciente]

Originally Posted by zeek

Would this be the best wavelength to simulate early morning light before the mains kick in?
What about afternoon/dusk? I assume a lower temp would be best for this application?
Isaac

According to my textbooks, early morning (dawn)sunlight is rated between 2000K and 2500K. So any bulb you can obtain in the 2000K to 3000K would be sufficient. For reasons of practicality, I would use the same color temperatures for the afternoon (dusk).

If you're lucky enough to have a 3 tube hood in which each light can be independently controlledy, I would light the tank as follows:

Let X=Early Morning Light Bulb
Let Y=High Noon Light Bulb
Let Z=Mid Morning Light Bulb

Early Morning: X
Mid Morning: XZ
High Noon: XYZ
Repeat in reverse for afternoon.

And durations should be obviously shorter. So "early morning" in your tank would be 30 mins, "Mid Morning" should be another 30 mins, and then 10 Hours of "High Noon". Then repeat in reverse for afternoon.

Gradual light changes are easier on fish, they don't stress as much as when the tank goes from dark to *BLAM* high noon. Which makes sense, cause if the sun did that to us in real life, we'd be a little freaked out too!

I hope this info helps.

-Viciente

[wayne]

'Plus fish in the wild are rarely subjected to complete darkness.' - if you've ever seen a blackwater river, or in fact a good number of freshwater rivers with a lot of sediment such as S American 'whitewater' you'll know that's not true. The fish can be in almost complete darkness during daylight hours as the light tranmissability is so low due to cheimcal colouring or just the volume of suspended sediment.
That's why most of amazonia has no aquatic plants either.

Given the 'money no problem' option I would not be overly concerend with spectrum but more worried about intensity and so on. If you really want to get out the cash Sfilligoi (1000 Euros and up) produce computer controlled electronic ballasts for metal halides with fades for dawn, dusk, clouds and so on...

http://www.tmc-ltd.co.uk/aquarium/sfiligoi-lighting.asp

[Viciente]

Wow... That lighting system is rather remarkable.... I wish I had the cash sittin' around so I could buy some.

[THUNDER]

Trying to figure out on the best lighting. So far, this seem to be the best one stated on this forum, unless someone correct me? Does anyone know where to find a 3 tubes hood with independently controlled lights timer online, because I cant find it?

Thunder

Originally Posted by Viciente

According to my textbooks, early morning (dawn)sunlight is rated between 2000K and 2500K. So any bulb you can obtain in the 2000K to 3000K would be sufficient. For reasons of practicality, I would use the same color temperatures for the afternoon (dusk).

If you're lucky enough to have a 3 tube hood in which each light can be independently controlledy, I would light the tank as follows:

Let X=Early Morning Light Bulb
Let Y=High Noon Light Bulb
Let Z=Mid Morning Light Bulb

Early Morning: X
Mid Morning: XZ
High Noon: XYZ
Repeat in reverse for afternoon.

And durations should be obviously shorter. So "early morning" in your tank would be 30 mins, "Mid Morning" should be another 30 mins, and then 10 Hours of "High Noon". Then repeat in reverse for afternoon.

Gradual light changes are easier on fish, they don't stress as much as when the tank goes from dark to *BLAM* high noon. Which makes sense, cause if the sun did that to us in real life, we'd be a little freaked out too!

I hope this info helps.

-Viciente

[Breene]

very useful. It definatly helps because im picking out lighting soon. I also vote sticky.

[bigfoot150]

Few things I would like to hit on that seem to be not entirely correct:

Freshwater aquatic plants require peaks in the red spectrum for optimal growth, as freshwater aquatic plants' photosynthetic ability is most sensitive to red light......

.....If one were to use a light source which produced peaks in the red and blue spectrums, the overall effect would look quite garish.

Plants use both the red and blue spectrum. Both are important for a healthy tank especially if you have plants that are red-ish in color. When selecting bulbs, you actually want bulbs that peak well in the red and blue spectrums, however, intensity(ie lumens/lux) is actually more important than the spectrum. However, it just so happens that most 6700K blubs provide a good level of red and blue spectrum along with good intensity. This explains why they are so popular.

With that said, I have actually kept tanks and seen others that used all 10,000k bulbs or all softwhite bulbs which I believe are ~3000K. The plants in these tanks grew very well.