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zfarsh 05-29-2011 09:57 PM

lighting question for planted low light tank
2 Attachment(s)
Hi All,
I have a new 75g tank that will be setup for low light. Light is that of a shop light with 2 bulbs that i originally put 6500K daylight. To save money, i bought play sand over tahitian moon black (say 20$ vs 100$). That said, the play sand looked very bad under the light condition, lost its warm tan/brown color for a light color. Yet i knew the sand looked good when i was cleaning it. I bought some soft white bulbs, that is 3,000K, and the sand looked pleasing again. What i finally did is have 1 x 6500k daylight bulb, and 1 x 3000K soft white, and i still have the nice warm color i wanted. I would have put 2 x soft white, but i want my plants to grow as well.
Question is, will this be enough light for low to medium light plants, specially when one of the bulbs is 3,000K ?? I would add liquid fertiliser to the tank.
See pics attached for difference between the 2.

zfarsh 05-29-2011 11:34 PM

some more precisions
22 to 26 inches from the sand floor (i made it adjustable), normally it is set to 25"
The 4ft shop light are 32W each bulb.

Byron 05-30-2011 11:50 AM

In my opinion, that should work very well indeed. I have two 4-foot T8 tubes over all my larger tanks, a 70g, 90g and 115g, and I have no trouble with moderate light plants. Some are 40w some 32w, the latter have much the same intensity but are more "energy-saving," ythat's all.

You also have a good spectrum. The 6500K combined with a warm will provide good light. Red is needed more by plants. Algae should be even less of an issue once you have the balance (light period plus nutrients) established.


zfarsh 05-30-2011 12:16 PM

Thanks Byron, what spectrum light are you using? I used the sand you recomended, but the 6500k alone makes look crap, the soft white 3000k is really bringing alot of nice warmth to it, making me like it so much, maybe even more than black sand.

Byron 05-30-2011 12:21 PM


Originally Posted by zfarsh (Post 687526)
Thanks Byron, what spectrum light are you using? I used the sand you recomended, but the 6500k alone makes look crap, the soft white 3000k is really bringing alot of nice warmth to it, making me like it so much, maybe even more than black sand.

I currently have one 6700K and one 6500K over the three larger tanks; a single 6700K over the single-tube tanks, and 6500K on the smaller tanks with CF incandescent.

I prefer a cooler rather than warmer appearance, but that is visual. Studies show plants need red and blue but more red, and algae tends to appear more with the bluer light. This is all very general you understand. If nutrients are balanced with the light period, the truth is that plants will grow under most anything. The rate of growth obviously depends upon the light spectrum and intensity and period plus the nutrients in balance, but healthy plants are healthy plants whether they grow fast or slow.


redchigh 06-01-2011 09:11 AM

If you're able, the absolute best combination would be 'full spectrum' beside a 6500k bulb. Many of the full spectrum bulbs look quite warm (around 3000-4000k) and would be a better compromise IMO..

Plants will likely grow well, if slowly under your light.

zfarsh 06-01-2011 03:30 PM

Hi, thanks for your inputs. I dont know what a full spectrum is (i thoughed it was 6500k till now). Basically, when going to HomeDepot, what should i pick. They have daylight (6500k), Soft White 3000K, and Cold White (i think it is 5000K), didnt see anythign else. Can you guys give me more details on this Full Spectrum?

redchigh 06-01-2011 03:52 PM

Aqua-glo, sun-glo, etc are full spectrum.

In a side-by-side study, cool whites alone out-preformed full spectrum, while the absolute best lighting was a combination.

If you want a full-spectrum without the price tag, then when you go to home depot, look on the side. Beside the lumen and color temperature, you should see a 'CRI' number.
Find the lowest CRI possible to go beside your cool white. If you want it to be warm, then you can just find the lowest CRI in the warm white/soft white area.

The bulb you have might even be close to full spectrum (low C RI), look into it.

Byron 06-01-2011 05:06 PM

I have to correct something here. Full spectrum is the closest to natural sunlight. The tubes that come close to this are Life-Glo, ZooMed's Ultra Sun, Phillips Daylight Deluxe, and Sylvania's "daylight" [actual name escapes me].

The Aqua-Glo and Flora-Glo and such are not full spectrum; they are mainly red and blue wavelengths. The Life-Glo is tri-phosphor, meaning it emphasizes the red, blue and green but is balanced with everything.

In terms of Kelvin, the sun is around 5500K. The value of using Life-Glo is that the heightened blue adds a bit of "cool" white to the mix. This is your combo of full spectrum and cool white that you correctly mention was proved to provide the best plant growth. Diana Walstad goes into all this of course, and in her last chapter I think it is mentioned that she always chooses tubes with a Kelvin of 6000K to 7000K to achieve this balanced light.

Now we have to assess this "grow best" thing. The fact is that aquarium plants will grow under any light. Their growth rate varies depending upon the light spectrum, intensity and duration, in balance with the nutrients. But they will live and be healthy with any reasonable light. It would be silly to suggest different, considering the decades of planted tanks that managed with the old incandescent bulbs that were well below 6000K. However, providing good light means better success, all else being balanced, and less opportunity for algae.


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