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 equatics 08-02-2012 10:17 PM

Help With Calculating Light Intensity On 10 Gal.

Hi. I read Hoppy's article on PAR and didn't understand too much except uMol / m2 / sec. I would like to calculate PAR for my tank and tube and hopefully be able to compare it to others'.

My tank is a 10 gallon. ~11" from tube to substrate, 20" long, 11" wide. The tube is T8 Aqueon 15W 18" "full spectrum".

W/Gal. = 1.5

I would fall back to lumens if this requires a meter.

Thanks for the help!

 DKRST 08-03-2012 04:16 PM

Hoppy's great, but I think you are over-analyzing the light issue! I apologize in advance if I'm being too basic here, but others will be reading this also. I have tanks ranging from high to low light. Some with pressurized CO2, some using glutaraldehyde (Flourish Excel), some very low light and low tech. I have a \$200 PAR meter, and I guarantee, it is less helpful than your eyeball and just observing the plant growth over time. My tank that has 4xT5HO bulbs actually has low light at the substrate due to plant growth!

The first question is, what plants do you want to grow?
That determines the light level you need. Just at a guess, I'd bet your light falls into the low or medium-low range, but the "range" is arbitrary as heck anyway!

Another way is to try some inexpensive plants. Broad-leaf plants like swords and especially anubias grow in all but the lowest light, but many swords will eventually outgrow a 10 gallon, unless you go for the smaller ones like Rosette swords. Add some stem plants in like Cabomba, Elodea (AKA anacharis or Egeris densa), rotalia indica, Ludwigia, etc. Note what works and what dies/fades out over time. Note any algae growth. Too much algae? That means either too high a light level or too long a photoperiod. Experiment. In general, stems require high light, broader leaves require less, and off-the shelf lights sold with tanks usually stink (low light), but start simple.

Planted tanks don't have easily quantifiable settings to make them perfect. I wish they did have a simple recipe to follow for perfection! It would save me a ton of money. Each tank is different. Enjoy the hobby by experimenting, that's part of the fun, if it works, great, if not, try something else!:lol:

Sorry if I pontificated, but I drove myself crazy trying to over-quantify the process of a great planted tank. It really is as much art as science sometimes!

 Quantum 08-03-2012 08:16 PM

you would need to know the exact spectral output and lux of the light in order determine the total number of light particles per square meter per second

first derive irradiance for each wavelegth produced (in watts per square meter) from lux (determine how many lumens for each wavelength present and convert to watts using the luminosity function curve), then using Planck's constant and the speed of light determine the #photons of each wavelength present/m2/sec and add them together for the total

but as DKRST suggests, this is all theoretical, what actually happens to the light particles in an aquarium with water containing dissolved and suspended solids and plants etc. will be quite different, so I agree just start with the empirical data and go from there

 equatics 08-04-2012 01:25 AM

Thank you for the reply. It sounds a little complicated for me. I have no way of getting a lot of the elements that you mentioned.

Since we're here anyway, would you be able to tell me how 15W / 10 gallons T8, or 1.5W / gallon with an 11" depth from tube to substrate is doing for me, can I grow any plants? Cabombba and Water Sprite are doing well.

Thanks.

Quote:
 Originally Posted by Quantum (Post 1183713) you would need to know the exact spectral output and lux of the light in order determine the total number of light particles per square meter per second first derive irradiance for each wavelegth produced (in watts per square meter) from lux (determine how many lumens for each wavelength present and convert to watts using the luminosity function curve), then using Planck's constant and the speed of light determine the #photons of each wavelength present/m2/sec and add them together for the total but as DKRST suggests, this is all theoretical, what actually happens to the light particles in an aquarium with water containing dissolved and suspended solids and plants etc. will be quite different, so I agree just start with the empirical data and go from there

 DKRST 08-04-2012 08:55 AM

Quote:
 Originally Posted by Nemo the Clownfish (Post 1184076) Thank you for the reply. It sounds a little complicated for me. I have no way of getting a lot of the elements that you mentioned. Since we're here anyway, would you be able to tell me how 15W / 10 gallons T8, or 1.5W / gallon with an 11" depth from tube to substrate is doing for me, can I grow any plants? Cabombba and Water Sprite are doing well. Thanks.
To get an accurate PAR, you really would need ti use a meter. One problem relating to the PAR level/light intensity has to do with a light fixture's reflector. A really good, properly angled, mirror-finish reflector behind the light increased PAR significantly. A poor reflector can take a bulb that generates "high" light levels with a great reflector to one that generates medium-low light when used with a poor, or no, reflector.

In my experience, Cabomba take ridiculously high light to maintain and to do wel long-term. I've never had much luck with it myself over a long time-frame, but that's just me. It grows like a weed for other folks I know. If your water Sprite's doing well, the probably indicates reasonable/good light levels at the substrate.

 equatics 08-04-2012 09:13 AM

Thank you very much for the help, someday I will understand PAR. You have been a lot of help, so thanks.

 fish monger 08-04-2012 09:49 AM

This is the first time that I have seen PAR in relation to aquarium lighting. It usually comes into play with flood or spot lights. This is an element that should be of no concern in all but the largest tanks. I have been in the hobby long enough to see watt per gallon incandescent through the latest technology. What makes the most sense to me is kelvin and lux (color temperature and intensity). The subject can be interesting and thought provoking to some folks and that's great...just don't give yourself something else to worry about.

 Quantum 08-04-2012 12:07 PM

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.

 DKRST 08-04-2012 01:20 PM

Quote:
 Originally Posted by fish monger (Post 1184287) This is the first time that I have seen PAR in relation to aquarium lighting. It usually comes into play with flood or spot lights. This is an element that should be of no concern in all but the largest tanks. I have been in the hobby long enough to see watt per gallon incandescent through the latest technology. What makes the most sense to me is kelvin and lux (color temperature and intensity). The subject can be interesting and thought provoking to some folks and that's great...just don't give yourself something else to worry about.
Respectfully disagree! PAR is probably THE best relevant measure of the actual "bang" you get from a light, in terms of plants ability to use the light. It's a measure of the photosynthetically active radiation that's optimal for plants to capture. An extreme example - Use a light with 7,000 lux that's the wrong spectrum (it would look odd to the eyes, color-wise), you won't get the growth you'd get from a 3500 lux light in the correct spectrum.

That being said, some serious high-tech planted tank folks have used PAR for a while, but you can make good estimates of light usefulness in the tank based on lux, the kelvin, and/or the general "spectrum" of the bulb (daylight, soft white, etc.). I wouldn't sweat the PAR too much. I happen to have a meter because I'm using it in one of my classes for some student research projects this coming fall.

+1 to Quantums comments!

 fish monger 08-04-2012 02:19 PM

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.

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