Help With Calculating Light Intensity On 10 Gal. - Page 2 - Tropical Fish Keeping - Aquarium fish care and resources
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post #11 of 14 Old 08-04-2012, 03:32 PM Thread Starter
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Originally Posted by Quantum View Post
PAR is only relevant to plants and other photosynthetic organisms (Photosynthetically Active Radiation), it is only indirectly related to human vision (lux and lighting design, etc.) because for the most part light that is photosynthetically active coincides with the visible (to humans) portion of the electromagnetic spectrum.

There are conversion factors that can be used to convert lux to photon flux, these are based on generalities and would be approximate: lux(0.013) for 'cool white' fluorescent according to one source.

PAR is a quatitative measure (#photons/area/time), but how would you know how many photons would be needed? You would have a number, but would that be too many photons per sec or not enough? It also would not tell you what specific wavelength light is produced, only that it is between 400 and 700 nm. You would need to know the spectral output of the source to determine if it is good for plant growth.

A single 18" T8 tube is adequate light to grow a lot of types of plants in a 10 gal aquarium. One suggestion though, if your tube is the 8000K one that comes standard with Aqueon fixtures, it may be worth it to get a better tube. One around 6500K will provide good light for plants and produce a whiter light rather than the pink hue those produce.
Quantum, several other people have remarked about the Aqueon tube that comes standard with their fixtures as having a color temperature of 8000 K and a pink color. I think that I have a different tube that came with the 10 gallon fixture - the apparent tube light color is white, no pink, and it gives a perfectly realistic color to the plants. I'm stumped. The tube is labeled "full spectrum", although it probably has a greater output in certain areas of the spectrum. I wish I could get some confirmation that my tube is more like a daylight tube.
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post #12 of 14 Old 08-04-2012, 04:37 PM
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Yeah, all fluorescent lights have an interrupted spectral output with 'peaks' at certain wavelengths rather than continuous as in incandescent sources. It is the balance of the peaks that determines the appearance. The right mix of blue, green, and red will yield a whiter light, approximating a true full spectrum source at about 6500K. Tubes that produce relatively less green will shift toward what is technically called magenta (like in my avatar, where the blue and red mix).

Since your light doesn't produce this magenta hue, it is likely not the 8000K one. Aqueon/Coralife (owned by the same parent company) does make a very nice 6700K daylight bulb (at least in T5, they may make it in T8 as well). I have the non-HO T5 version and like it a lot nice plant growth and very good color rendition.
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post #13 of 14 Old 08-04-2012, 05:38 PM
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Originally Posted by fish monger View Post
Well. I think I mentioned the balance between color and intensity but, I'll have to admit that this is all beyond me. I also think that it is yet another confusing, redundant statistic.
Fishmonger - You did mention it, I just responded in too much of a hurry, sorry. I totally agree with you that not getting too focused on the tiny statistical aspects that can be overwhelming, is the best way to go.

Nemo, the "daylight" tubes are usually in the correct range for good plant growth, somewhere around 6500K, as Quantum already mentioned, is about perfect. They should show colors like, well, daylight. Although, I thought as the K moved higher, light tended toward a blue tint? I defer to Quantum on that!

18 species/varieties of fish, 15 species/varieties of plants - The fish are finally ahead of the plants!
*560 gallons (2120 liters) in 5 tanks -> you do the math.
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post #14 of 14 Old 08-05-2012, 08:29 AM
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Although, I thought as the K moved higher, light tended toward a blue tint?
Yes, the higher the Kelvin (degrees Celsius + 273) the 'cooler' the appearance the higher the temp, the higher the energy and since wavelength is inversely proportional to energy, higher temp sources emit shorter wavelength light (blue is shorter, red longer). But, Kelvin in this context technically only really applies to incandescent light sources actually at that temp. Fluorescent lights don't operate at those temps and any K rating applied to them is just an approximation as to how closely they replicate incandescent sources, so K ratings of fluorescent lights can be a bit inexact.

But the magenta hue from the 'plant grow' or 'aquarium' bulbs like the Aqeon 8000K is not 'warm' in the way that red light is. It is mixture of 'cool' blue and red, which are not adjacent to one another on the visible light spectrum. As such, it does not have a corresponding wavelength and is just a perception of how we interpret a mix of these two colors.
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