how to determine K rating for lights - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 04-13-2006, 10:11 AM Thread Starter
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how to determine K rating for lights

hi guys ive been told and found out a lot of times that the K rating for lights are critical and correct me if im wrong but as far as ive researched, 65000K is the best but how do we know what K rating our light are currently giving off?

im currently using 2 osram 23 wats compact floursecent light over my 10 gallon tank
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post #2 of 7 (permalink) Old 04-13-2006, 10:42 AM
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well, I'm not an expert myself, so hopefulle someone else comes along soon...

As I understand it, it's not really the K-rating that matters, but the wavelength. Chrorophyll a absorbs light in the red spectrum, about 660nm and chlorophyll b in the blue spectrum, about 470nm. I can't remember the numbers excactly. In addition, some algae contain chlorophyll c, but I can't remember the absorbtion spectrum for that. b and c are accessory pigments, so the light absorbed from these need to be transferred to chrorofyll a molecules for photosynthesis.

Anyway, the K-rating can be used to approximate how good the light is for plants, ie if it contains much of the correct wavelenghts. The higher the rating, the "cooler" the light seems. What you're aiming for (I think) is 5500K +. If the bulbs are not marked with kelvin, they are often marked as "warm" or "cold" light. The "warm" light is usually 2700K and the "cold" 4000K. If you haven't bought the bulbs specifically for plants, it is likely that they have one of these ratings. And so, you probably want to search for bulbs with higher rating. I've never seen cf lights above 6700K, but this should be fine.

Hope this helps, and that someone who knows more chimes in...
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post #3 of 7 (permalink) Old 04-13-2006, 11:23 AM
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If they are the spiral shaped bulbs they are 3000k. That's the only color Sylvania (maker of Osram lamps) manufactures in those bulbs @ 23 watts according to their catalouge for 2005-2006.
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post #4 of 7 (permalink) Old 04-13-2006, 12:08 PM
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Quote:
Originally Posted by gbhil
If they are the spiral shaped bulbs they are 3000k. That's the only color Sylvania (maker of Osram lamps) manufactures in those bulbs @ 23 watts according to their catalouge for 2005-2006.
In Asia, huge lamp players like philips and osram make wide variety of bulbs. The spiral one can be warm white (3000K), cool daylight (4000K) or daylight (6700K).

Quote:
as ive researched, 65000K is the best
It is 6500K and not 65,000K

To determine the Kelvin temp rating (according to an article in the krib), the manufacturer would compare the output colour of the bulb to a black body (carbon) which is heated to a certain temperature. As the body is heated, it will emits light. The temperature in K degree on which the body glows to a certain colour is the Kelvin temp rating. For example at 2000 degree Kelvin the body emits reddish yellow light, hence a 2000K bulb emits more or less the same.

Manufacturer's kelvin rating does not guarantee the spectrum of light the product emits. It is more of the end result combination of a bulb that emits several kind of colour spectrum. So be sure to pick something like specialty or daylight (simulates day light, which contains beneficial spectrums) of 5000K - 10,000K.


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post #5 of 7 (permalink) Old 04-13-2006, 02:06 PM Thread Starter
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so that means i should have bought daylight instead of cool daylight? nice info guys thank for sharing it with me

additional question though. does this also mean that if my bulbs are cool daylight it would more or less have this equation: 2 cool daylights = 1 daylight bulb? is it directly related to the efficiency of the bulbs to make the plants grow?
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post #6 of 7 (permalink) Old 04-13-2006, 02:27 PM
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K rating is the kelvin temperature of the bulb. It measures the color spectrum that is emitted from the bulb based off Hydrogen burning at that temperature. Each color temp puts off light at different wavelenghts, so actually, color temp is directly related to wavelengths. Some bulbs however are more stable and depending on how they make the bulb, they can produce a better wavelengths for plants. The reason to get a particular spectrum of bulb is because as you go further down water, particular spectrums of light, higher energy shorter wavelength, don't make it down. Cooler temp make it down further. So since most aquariums aren't more than 30 or so inches deep, then we need to change the bulb accordingly to reflect water dept. Hecne why in reef tanks the bulbs we use are so blue. At around 6 feet 95% of the light making it down is in the blueish spectrum.
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post #7 of 7 (permalink) Old 04-13-2006, 02:28 PM
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And 2 cool daylights don't = 1 daylight. Look on the box at the spectrum. 6700K is a pretty standard good bulb for freshwater plants.
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