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Discussion Starter · #1 ·
I have a 14g tank 16 1/2" tall. The stock lighting fixture is for 2 horizontal screw in type bulbs so I put in 5000K-14 watt CFLs. I have 2" of eco-complete for substrate. The bottom of the bulbs rests approximately 2" above the water. There is a metalic reflector in the hood just above both bulbs.

I understand it is 2 wpg, but that doesnt matter as much as PAR, however I have no idea how to measure that. I could not find 6,500 -6,700K CFL bulbs at my home depot so i just got the 5,000K.

I have java ferns and moss, anubias and a few types of stem plants.

Is that enough light for a low tech set up? Also I am confused about the K rating when using multiple bulbs. Do I have 10,000K in my tank now or just 5,000K?
 

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Color temperature (K) rating is not additive. It's a measure of the color of the light from the bulb. Flourescents tend to be more blue and incandescent tend to be more orange/yellow when compared to sunlight at noon. Cheap CFLs tend to be orange for some reason which is a low color temperature in the 2700K range.

I use 2 13W 6500K CFLs on my 10G but I may try the DIY Power Compact project.
 

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The low color temperature is to trigger flowering generally, and since most aquarists want their plants purely in the vegetative stage and most will not flower underwater, there is not much of a use for anything other than 6500k bulbs.
 

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I have seen no data that shows any difference in plant growth with any color temperature bulbs. There probably is some small difference, but practically speaking, you can use whatever lights look the best to you, assuming you use enough bulbs to get the brightness you need. Plants will grow with incandescent bulbs, with their very low color temperature, and with 10,000K bulbs. Of course getting enough intensity from incandescent bulbs is very difficult considering the amount of heat you then have to get rid of. But, my first aquarium, a 10 gallon one, had vals growing well with incandescent bulbs.
 

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Discussion Starter · #7 ·
Color temperature (K) rating is not additive. It's a measure of the color of the light from the bulb.
Thank you daijoubu, I have been wondering about that. So even if I have 20 bulbs at 5,000K each the temperature of the light is still only 5,000K.

The low color temperature is to trigger flowering generally, and since most aquarists want their plants purely in the vegetative stage and most will not flower underwater, there is not much of a use for anything other than 6500k bulbs.
Thank you for posting, I had no idea the color temperature had anything to do with flowering. I don't understand "there is not much of a use for anything other than 6500k bulbs" It would make sense to think that a the period which taxes a plant for energy the most would be when it is flowering. Therefore I would think that the plant will still grow with lower temp lighting.

you can use whatever lights look the best to you, assuming you use enough bulbs to get the brightness you need.
Hoppy, I must have missed something in my review of all these lighting posts. If the K temp is not what I should be concerned about for plant growth and health, yet "brightness" is, what measurement depicts brightness on a products package? Lumens don't matter to plants, are we saying PAR? I do get that, but have no way of knowing how to measure that.
 

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Hoppy, I must have missed something in my review of all these lighting posts. If the K temp is not what I should be concerned about for plant growth and health, yet "brightness" is, what measurement depicts brightness on a products package? Lumens don't matter to plants, are we saying PAR? I do get that, but have no way of knowing how to measure that.
Every type of bulb normally used for an aquarium has a characteristic brightness, which is the PAR value at a specific distance from the bulb. But, that number isn't available, and probably isn't even measured by the manufacturer. Most of our bulbs are fluorescent type, where the wattage is proportional to the length of the bulb, whether the tube is coiled for a power saver, screw in bulb, or straight for a T5/T8 bulb, or doubled back for a PC bulb. If you can measure the PAR output for one T5HO bulb, for example, you can predict reasonably accurately what the PAR value is for any T5HO bulb, and the same is true for T8 or PC bulbs. The fly in the ointment is that the PAR output also heavily depends on the quality of the reflector used. So, any comparison has to be between lights using the same quality reflector.

Many aquatic plant clubs now own a PAR meter, so if there is such a club near you, join it and borrow their meter. Then you can measure your own light accurately.

Otherwise, I have posted charts here that let you guess what PAR you will get from any T5HO or AH Supply PC bulb.

Lumens are weighted to a spectra that matches typical human eye sensitivity, so it isn't possible to accurately relate lumens to a PAR reading the bulb will produce.

Color temperature for a fluorescent bulb is largely a number assigned to help sell the bulb, although those numbers do correspond approximately with how the light looks - lower numbers tend to look more yellow and higher number look more blue-white. But one manufacturers 10,000K bulb won't necessarily give the same appearance as another manufacturer's bulb rated at 10,000K.
 
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