Kelvin vs Spectrum

CHINABOY1021

CHINABOY1021

experienced newbie
May 2, 2003
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im confused on which bulb i should get for my 20 gallon. ive read too many times that plants "use" 5000-6500K. but GE 9325Ks are good because its high in both the red and blue spectrum, which plants use most.

so i dont know if i should get a 5500K zoomeds, or 18000K aqua-glo.

heres a spectrum graph of aquaglos made by hagen.
diagaqua.jpg
 
CHINABOY1021,

why does so many people recommend something in the 5000-6500K range?

--Because this is the range that most closely duplicates natural sunlight. Colors will appear similar to natural sunlight. People recommend them, often mistakenly, because they think the plants 'need' this range. The plants don't care. Observers of the aquarium do. Lights with a dK rating above the 6500 level will appear whiter and those below will appear more yellowish.

Plants care mostly about power, wattage. They will adapt to just about any spectrum of bulb as long as it provides enough wattage for growth.

HTH

PP
 
thanks for the info. i think there's another flaw people might have been mistaken with. lower the kelvin the redder and higher the bluer, i dont think this is true because my friend uses aqua-glos and they're all pink. but he uses power glos which are also 18,000K that is white. ^^
 
It is correct that the range 5000-6700 K is likely to give a more normal appearance/color rendering than higher or lower K tubes. But it is not necessarily the case. A high K tube may have a higher CRI (Color Rendering Index - the appearance of color compared to the same color in natural sunlight) that a "normal" range tube.

But what the plants care about most it the amount of light delivered to them - so output and reflectors play a big role there. Wattage is only part of it, efficiency and delivery are equally important.

People care about CRI and appearance, plants do not. I am one of those people. You can say and even prove that tube xyz produces the best light for plants to use, but if the tank looks yellow, or blue, or whatever, I will not use it at all. I want the tank to look good to me, and look "natural" to others. If it does not, I don't care how perfect the sprectral match is to PAR (Photosynthetically Active Radiation) or PUR (P. Used R.), it is not suited for display tanks under my care.
 
As fas as lighting goes, I've done my experimenting and will always use a Kelvin rating between 5,500K and 6,700K.

I've had 10,000K's and hated the washed out look they gave. They belong with saltwater tanks - along with Actinics.
 
Robert has made some fine points. PAR is important to the plants and CRI is something I think that the discriminating viewer cares about.

In the end, if you have a multiple bulb holder you can mix bulbs to get the desired effect. Bulbs can be had at hardware stores for only a few $ each.

HTH

PP
 
From all the research I've done, the recommended Kelvin range for aquatic plants is 5000 K to 6500 K. Above 6500 K the light becomes more blue, and this is beneficial to algae, not to the higher plants. This is why the actinic bulbs and bulbs in the 10,000 K range are used for reef aquariums. Reef animals have corals that have the symbiotic algae that prefer the blue end of the spectrum. Aquatic plants like the red end of the spectrum which is in the 5000 K to 6500 K range. In the beginning I used 10,000 K bulbs I hade left over from my marine tank. The only growth that occured in my tank was with the algae, not the plants. When I switched over to 5500 K full spectrum bulbs, my Amazon Swords really started growing.
 
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