# Woah, 4200k is awesome for aquariums



## hunterlook (Feb 21, 2013)

Be careful with plant growth with that low of a Kelvin rating. You'll probably still get some but it may be slower than usual as they like more natural light around 5500K-6000k. 

I'm really curious about how this looks though, do you have any pics?


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## taiwwa (May 6, 2012)

Okay, some info:

6500k. Lights of America aquarium bulbs from Walmart. it's like 2x 15watt CFLs










Lights of America t8 4200k grow light, 17 watt.










Both pics taken with a Olympus DLSR using a 2x macro filter and 4.5 aperture and 1/25 shutter speed.


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## hunterlook (Feb 21, 2013)

Great color pop from that bulb!


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## Steve001 (Feb 26, 2011)

Blue light which this bulb has will make greens and reds pop.


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## BBradbury (Nov 8, 2010)

*Aquarium Lighting*



taiwwa said:


> I picked up a cheap grow light from walmart. It casts a purplish light so I tested it on my aquarium fish.
> 
> It makes the aquariums look much cooler. Too bad you really can't get CFL's in 4200k


Hello tai...

If you like the effect of a light in this spectrum then definitely use it. It's the wrong color if you want to grow aquatic plants, though. You need a bulb in the 6500 - 6700K range. The light blue color of this bulb comes closest to natural daylight at 5500K and is recommended for planted tanks.

B


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## taiwwa (May 6, 2012)

So aquatic plants need different spectrum from terrestial plants?


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## xmas_one (Feb 5, 2010)

Color temperature doesn't mean a whole lot without seeing the actual spectral output of the bulbs. Color temperature is like an average of the output that doesn't describe all of the peaks and valleys of the spectral plot. You can't really say one color temperature grows plants good and another does not. I might not be describing it really good, but look into it and you'll see what I'm saying. Case in point are led grow lights, they grow plants extremely well but the color rendering is terrible.


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## Steve001 (Feb 26, 2011)

taiwwa said:


> So aquatic plants need different spectrum from terrestial plants?


No, they need the same wavelengths. but we don't use light sources that produce just red and blue like this bulb does, because it makes things look garish. If you do a Google image search or just look at members tanks by clicking the Your Tanks tab or the Photo Gallery tab you will see without exception people light their tanks so they appear natural or close to natural in color.

You will notice that a majority of people here recommend a 6500K bulb which has a predominant output spike in the blue. People do so I think, because they either consciously or not like the way it makes greens and reds pop. The bulb is ok to use because it just so happens that enough red and other colors are produced to make plants grow. however, none of the tropical plants we can reasonably cultivate under tropical conditions grow where the Sun's light is 6500K. It is in actuality 5500K in the tropics and into temperate regions.


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## milesm (Apr 4, 2006)

BBradbury said:


> Hello tai...
> 
> It's the wrong color if you want to grow aquatic plants, though. You need a bulb in the 6500 - 6700K range.
> 
> B


b, i think color temperature has less to do with aquatic plant growth than par. check out post 21 on this thread: http://www.plantedtank.net/forums/showthread.php?t=85667&page=2, diagram4.
as can be seen, the 3200K bulb in fact produces more par than the 5500k bulb. plants need par; we need k for aesthetics.


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## Smitty06 (Mar 25, 2012)

Yes, but the sun is really in the 5500K range, and that is with all of the necessary wavelengths and enough to make it look very bright to our eye. Even though par should be very reliable, I always like to see a spectrum chart in order to make sure it is not just a false reading.


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## taiwwa (May 6, 2012)

So someone explain to me this:

4200k =/= purple light, apparently.

So why does this unit give off purple light?


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## micheljq (Oct 24, 2012)

Hello,

The sun color temperature does not stay the same at a time of the day. It varies a lot from the morning to evening, and will be very different between a sunny and cloudy day.

It can be near 4000k in the morning, and 6500k at 16h00.

It will be different also depending on the latitude.

My friend did grow java moss when I was young with a cheap incandescent 3200K light bulb. It did outgrow his 10G tank.

Personally I had success growing plants with 5000, 6500, 10000k color temperatures, either fluorescent bulbs, CFL bulbs, or Leds, no matter plants were growing.

So of course you can grow plants with your 4200K bulb, I am not surprised at all 

Michel.


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## gSTiTcH (Feb 21, 2013)

Plants utilize all wavelengths of light. They do use some more efficiently than others. If you want to truly mimic the Sun's output, find a high intensity ($$) full spectrum bulb. Otherwise, go for a high intensity regular bulb.

If I remember correctly, Red encourages more leafy/flowery growth while blue encourages stem growth.

I personally use a mixture of GE Daylight (6500K) and GE Office (3500K) bulbs. Probably not the best as far as CRI goes (which is how we perceive the light, regardless of its K rating), but my plants, fish, and aquarium observers are all very happy. I tried all 6500K bulbs but they seemed to stymie the growth of plants.

Based on my limited experiences talking to people and visiting other people's aquariums, we tend to overthink this as hobbyists.


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