new lighting questions

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yallyall1

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Hi guys!

My lighting for my low-light simple planted tank has failed on me... one has blown out and has stopped working, so that leaves me with 8w which is clearly not enough!

I am hoping to get a 6700k bulb with somewhere between 12w and 24w (would I need co2?) and hopefully turn it into a medium-light planted tank!

any advice on the kelvin rating or wattage? I am a complete noob when It comes to lights, so please help!

BTW, They have to be 30cm T5's
 

mathas

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yallyall1 said:
any advice on the kelvin rating or wattage? I am a complete noob when It comes to lights, so please help!

BTW, They have to be 30cm T5's
"Kelvin rating", to me, is rather unimportant. It will give you a good idea of what color the light should look to you, but will not give you any real indication of whether or not the light is any better or worse than similar bulbs as far as plant growth goes.

For wattage, match the bulb to your ballast. 30cm is shorter than the smallest T5 I've seen here in the States, so I'm not sure what the standard wattage for that length would be. If the ballast doesn't indicate what type of bulb it's designed to drive, I would stick with the same wattage as what you currently have. If you fail to match the bulb to the ballast, you dramatically increase the likelihood of a shortened lifespan of bulb or ballast or both; and in extreme cases, fire.
 

bass master

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mathas said:
"Kelvin rating", to me, is rather unimportant. It will give you a good idea of what color the light should look to you, but will not give you any real indication of whether or not the light is any better or worse than similar bulbs as far as plant growth goes.
What about chlorophyll absorption? Ive heard that lights in the 5000-10000k range are best for planted tanks because they offer the correct wavelengths of light that the plants absorb best. Is there some truth behind that, or is it mostly just speculation?
 

mathas

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bass master said:
What about chlorophyll absorption? Ive heard that lights in the 5000-10000k range are best for planted tanks because they offer the correct wavelengths of light that the plants absorb best. Is there some truth behind that, or is it mostly just speculation?
That range tends to emit light in the correct spectra for freshwater plants, but there are exceptions; there are bulbs in that range that are relatively bad for plants, and bulbs both below and above that range that are good. And even if you're within that range, there is really no way to know by correlated color temperature which bulb is better or worse. The correlated color temperature ratings that are somewhat arbitrarily-assigned to bulbs have to do with human color perception, not actual spectral equality.

To specifically address your chlorophyll question, chlorophyll a absorbs light most strongly around 430nm and 660nm, and chlorophyll b absorbs most strongly around 450nm and 640nm. Given that, which is better, 6700K or 10000K? Hint: correlated color temperature doesn't even come close to answering this question. Recommending a specific cct value, as yallyall1 asked for, is meaningless, largely due to metamerism.

In short, all correlated color temperature tells you what color the light should look to most human eyes. If you want to know what type of light is actually emitted (by wavelength), look at the spectral power distribution graph for the bulb, which should be on the packaging.
 

bass master

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wow.... as always I'm impressed, thanks mathas!
 
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yallyall1

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Thanks for the advice, I can get 30cm T5's quite easily here!
 

Kunsthure

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bass master said:
wow.... as always I'm impressed, thanks mathas!
Lesson learned: don't question mathas.

-Lisa
 

bass master

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Kunsthure said:
Lesson learned: don't question mathas.

-Lisa
oh, I would never question Mathas! I was just educating myself
 
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