Proper Light For Planted Freshwater Tank

[Vanterax]

I'm a bit new to this so be gentle with me... please...

I received a new light fixture that came with 4 T5HO bulbs. 2 10000K and 2 Actinic bulbs. Sounds to be like this setup is more for a reef tank than a freshwater tank. Although I like the blue glow of the actinic bulbs, will fresh water plants benefit from those lights in any way? Also, is 10000K the right temperature for fresh water plants? I did some reading and the consensus seems to be that the 6700K range is preferred.

I'm trying to figure out if I should be replacing those bulbs. My tank is 46g bow front.

[Iceturf]

5000 - 10 000 'k' is the right 'temperature' for fresh water plants. Actually there is a funky light that is somewhat purplish (said to be 9350k but doesn't look at all like 10000k) which is considered to be optimized florescent light for plants (more of the light produced happens to be the type that best stimulates chloroplasts). Short of finding a light that produces only the specific frequencies of light that chlorophyll responds best to, anything in those two ranges and your good. The rest is more of what you like.

PS, Chloroplasts respond to a range of frequencies around and near certain 'key' frequencies (certain red, yellow, blue frequencies), so most visible light can be used by plants for energy; plants also adapt their chlorophyll production to optimize energy for the lighting conditions. However, due to technology limitations we cannot produce just those frequencies where conversion is most efficient. We rely on the lights we provide to have enough all over the place spectrum distribution that the plants make do. So 6500k is typical, I prefer the look of 10 000k but either is fine (and 6500 is sometimes cheaper). Just note higher waste UV light/nearUV produced the higher 'k' you go. Most of it gets filtered by the light bulb glass itself, some of it by typical light covers, some by water, some by aquarium glass, but you will be exposed to more stray UV the higher K you go..... 400nm can still do damage to your skin but escape glass filtration.

Edited January 11, 2013 by Iceturf

[ckmullin]

Those Actinic are meant for salt...the freshwater spectrum is more in line with 67k. Sell the Actinic and buy two 67k.

If the fixture has the ability to have different sets of bulbs on or off...make sure one 67k and one 10k are always on together.

[jewels]

This is a plot for a 10K bulb . Not much red there.

This graph shows the output of an actinic bulb. Red is absent.

These spikes that appear here show us what plants would enjoy most readily.

The previous replies make sense to me.

I have never owned either of the bulbs you mention. As such I have never measured their output. Nor have I tried to grow plants with them.

Given your situation I would play devils advocate and buy two lower K bulbs That will add some red to the mix; as would natural sunlight. Try them in different combinations until the appearance is pleasing to your eye.

Then blame me if the plants dont grow. :shock:

[jeremoose]

6700k and 10000k are a really nice mixture both for growth and the appeal of how they look together.

[Vanterax]

I've seen bulbs rated in wavelength or color temperature. Never both.

I was thinking of getting two Coralife Colormax (350-750nm) and it seems to be a good choice based on the chart above. Then again Coralife also has 6700K "plant lamp" bulbs for the same price. Are they both roughly the same?

[Znaika]

Colour Temperature (K) = 3,000,000 / Wavelength (nm)

Wavelength (nm) = 3,000,000 / Colour Temperature (K)

Therefore:

10,000 K lamp peaks at 300 nm

6,500 K lamp peaks at 460 nm ...but both, of course, radiate albeit with lower intensity outside of these peaks too.

Solar spectrum:

The peak is at 500 nm or 6000 K, however 50% of the radiation power or above is spread over the range from 350 nm to 1000 nm, thus 3000 K to 8600 K

Chlorophyll absorption peaks fall onto 6500-7500 K and on 4450-4650 K

Standard 48" T8 daylight tube, which is sold in The Home Depot and elsewhere for $12 a pair has colour temperature 6500 K. Standard 48" T8 cool white tube - 4100 K

Combine the two in the same 48" light fixture available in the same place for $22 - and under $40 you have a solution which otherwise will cost you hundreds. I am sure the situation is the same with shorter tubes.

[Vanterax]

Thanks everyone for the good info! It is completely clear now.