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What type of lights to plants need?

Full Spectrum vs, 6,500K, 10,000K Daylight, other K rating,etc...????


I am considering replacing one of my lights since it has water damage and wondering what type of spectrum to be looking for. I don't know if I can trust some of these Ebay sellers just because they label something as " plant"

I would like to grow my plants better but not so much Algae. My last light made algae on everything it touched.

Thanks.
 

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Plants use a lot of certain red wavelengths, and a lot of certain blue wavelengths.
They use a lot less of the greens and yellows.
A PAR meter, or the PAR test results will tell you which bulbs offer the best PAR value.

People see the yellows and greens better than the reds and blues. A bulb that is bright to our eyes may not offer much energy to the plants.

The K value is a number that represents what our eyes see. It is a blend of wavelengths, but just looking at the K value you cannot tell what the different wavelengths are. In a general way you can say that a low K value (couple of thousand) is more likely to have red-orange-yellow wavelengths and a high K value (10,000) is likely to have mostly blues. An in-between K value (say about 4000-6500) is probably going to have some of each. But is also likely to be more heavily weighted in the yellow to green range so that we will see that as a good, bright light.
'Daylight' bulbs might have a better range.
In all of these, look at a chart on the package (if there is one) and you can see which wavelengths are most prevalent in that bulb.

When I used a lot of fluorescent bulbs I would combine a 'Plant' bulb with a 'daylight' bulb so each tank had 2 or more bulbs.
The plant bulb looked sort of dim, more pink-purple. Sure made some fish look funny! The daylight bulb balanced it out so that to my eye the tank looked natural, the fish and everything in it looked right. When I could not get a plant bulb to fit the fixture I would look for a Daylight, or a Cool, or, last of all, Warm. A combination, IMO was usually best, with the idea that what one bulb lacked, another would supply.

Now that PAR values are becoming more common, use these whenever possible. A 'Plant' bulb, or a bulb sold for planted tanks sure ought to have the PAR value on the package. Other bulbs might have been tested, but you may have to research to find it.
Look here at TPT, I think there was a sticky that included PAR values, measured by members, for a lot of different bulbs. Also look at the manufacturer's site. This info might be listed there.
 

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I have grown plants in every spectrum from 2700K to 18,000K.
Most seem to think that between 5000 and 8000 is best for plants.
Most E-bay fixtures don't mention K values anyway so why be concerned with
what K value works better. Why not state the size of the tank, the intent of low,
med or high teck and just ask what people have on a tank that size and level of light.
Surely there are a few who have that tank and a couple in whatever light level
you intend to use. They can let you know what they have on their tanks.
 
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