finfollower

hey all,
I'm just wondering if I need to get different lighting. Right now I'm using 2 13W CF bulbs that have a color temp. of 2670K. I know that 5500K is the closest spectrum to natural sunlight, but do I need to change my bulbs to something that's around 5500K or can I keep using the ones that I am using now?

John N.

The lowest I ever used was around 4000k. The light did an okay job at growing my plants. But once I bumped it up to 6500k I noticed a growth difference, not to mention the plants just looked better under this spectrum.

Are you using the screw in variety? If so, it shouldn't be too hard to walk over to walmart and pick up some 6500k bulbs. In my opinion, anything under 4000k doesn't look good, and doesn't grow plants well. I don't know the exact science why that is, but it is what it is.

-John N.

finfollower

yep, i'm using the screw inu CF spiral bulbs.

Newt

Lighting for a planted tank should not be chosen on color temp alone. It is true that 'full spectrum' bulbs are referred to as bulbs between 5000 Kelvin (K) and 6500 K and are best for planted tanks. Yet this does not indicate what type of light (wavelength in nanometers) the bulb is actually emitting. If you want both good leaf development/growth (blue light) and stem elongation (red light), you need light in both the blue and red spectra for photosynthesis.

You need a mix of blue and red for your plants, and green for you (brightness as perceived by humans). If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum. Do not equate this with good lighting for your plants, because plants don't use light in the green spectrum for photosynthesis.

For green plants the lighting peaks that are most important:
chlorophyll-a: 430nm/662nm
chlorophyll-b: 453nm/642nm
carotenoids: 449nm/475nm
Red pigmented plants use more light in the blue area of the spectrum.

Beyond choosing lighting that is optimal for photosynthesis, as above, you should choose lighting with the color temperature that best suits the aesthetic goals of your tank. So, don't obsess about color temperature beyond how you want your tank to look. From a color temperature standpoint, blue-colored light will enhance blues in your fish. Green-colored light will make the tank look bright to humans and enhance the green color of your plants. Red-colored light will enhance the reds in your fish, and any red plants. If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum.

I have attached some jpg's to help understand lighting and how plants react to it. I have found it best to provide a mix of lighting to a planted tank. The GroLux bulb is perhaps the best plant bulb available but it has very little green light so the visual effects of your tank will look dim and purplish. Yet if you add some other lighting such as a Philips 6500K the effect is more pleasing to the eye and still beneficial to the plants.

finfollower

wow, thanks a lot for the info newt. I've never really thought of the aesthetic part of the lighting until I changed my bulbs recently. I liked the 2760K a lotbetter than the 6700K, but it wasn't as beneficial for my plants. What about mixing the two bulbs, what temperature would my lighting be rated at or would it still remain the same?

Newt

I just scanned some new graphs that may help understand more:

hedson_25

hello newt, i`m so interested in these theme, lighting, so you said that the best option are gro lux, could you tell me the nm and ºk of these fluorecent bulbs, and with what combination are they the best for planted tanks?

Newt

I use a 40 watt grolux standard and a 40 watt grolux wide spectrum (both linear fluorescent) and (2) 55 watt Philips PL-L 950 CF. The Grolux standard has no kelvin rating. The wide spectrum is 3400K and 89 CRI. The Philips CF are 5000K and 91 CRI. Nanometers as displayed on attached spectral graphs:

Newt

Seems this site doesnt like the size of my pdf file for the grolux graphs. I will see if I can reduce it.

DJKronik57

So are true actinic bulbs beneficial for planted tanks or not? 420nm is near but not inside any of those ranges you gave for essential plant functions. What about 10,000K?