|02-21-2014 01:41 AM|
Here is a good article explaining what "PAR" is, by Li-cor, who make the best PAR meter in the world, as far as I can find out. http://www.licor.com/env/application...hetically.html
All PAR measurements I have heard about or seen, use PAR to mean photon flux per square meter per second, which means it is a measure of the light intensity at a surface, not the light emitted by a source of light. I would welcome a link that says PAR is a measure of the light emitted by a source of light.
Here is another article that somewhat clears up the difference between "PAR" as a measure of what the light source produces and what the intensity of light at a surface is. http://openwetware.org/images/e/e8/Conversion_lux.pdf It seems that our "PAR" should always be called "PPFD" instead. But "PAR meters" don't measure the total emission of light from a source, but the PPFD at the surface being illuminated, a much, much more useful parameter.
Curiously, note that, for a cool white fluorescent source, the factor to multiply lux by to get what we call PAR, is .013, or 1/77, remarkably close to the 1/78 that I found experimentally.
|02-20-2014 09:59 PM|
From the data accumulated at http://www.apsa.co.za/board/index.php?topic=4454.0 (in 2010) it is calculated that, on average, you get about 1 PAR/W from tube/fluorescent lamps (T8 & T5). (T5s are only marginally better for output and this is due, mostly, to geometry.) So a 20 W CFL will put out as much PAR as a 20 W T8 tube (because the physics of light emission process is the same). Of course the CFL is all twisted and a lot of light is lost among the twists and turns of the tube (especially as about 30-40% of the light emitting surface is facing another light emitting surface and gets lost by "squishing").
The major factors (that will vary with each aquarium setup) are the turbidity of the water (the more light absorbing dissolved solids the more light is absorbed with depth), the amount of light lost to reflection due to surface disturbance or angle of lamp to water (90% of the light hitting the water at 60o is reflected and it gets worse the shallower the angle). You need the lamps as close to the water as possible to keep the angle of incidence steep. The quality of your reflector is also critical. With a bad reflector you are probably getting less than 50% of your light into the tank. With no reflector the value is closer to 30%. A model to determine reflector efficiency is available at http://www.apsa.co.za/board/index.ph...41393#msg41393 .
Essentially, if you can engineer a reflector with high efficiency and place it so that as much light as possible hits the water's surface of the tank, then you can, with some certainty, use W/m2 to estimate PPF at specific water depths.
So, to summate by example: if you have two 30 W T8 tubes they are emitting approximately 60 PAR. If you have a good reflector that can focus all the light into the tank (which is impossible but lets just pretend) which is 36 x 12 inches in surface area you will get 222 PPF (PPF = PAR/(0.9 x 0.3 m)). Assuming 70% of the light actually enters the water, this will mean you will have about 99 PPF at 15 inches of water depth (not tank depth). More than enough for Glosso and HM and unless you have ample CO2 and nutrients you will get an algae soup. Without reflecors the value would be closer to 30-40 PPF which attests to the old adage that 2 full length tubes are enough to grow just about any plant.
I'm having a hard time understanding this and it's relation to the chart. I have a 5.5 G tank with a 13w 6500k CFL about an inch from the surface in hood with no reflector. So I'm reading this noticing I'm losing a ton of light due to it being parallel to the surface and without a reflector but unless I'm reading the chart wrong since my bulb is probably 8 inches from my tanks lowest point my par is extremely high. I'm just trying to figure out what my par is and what category it falls in. Judging by the coloration of my plants I always thought it was low to medium-low at best. Am I opp operating at 1 p/w? So I'd need a 30w cfl for my 5.5g tank. My betta would probably think he's in the interrogation room
|10-20-2013 06:02 PM|
This is a lot of information to take in and I commend you on the effort you put forth. My question is, how to really utilize this information? Many websites that talk about planted tanks give plant lighting requirements in watts/gallon. I am not sure how to convert the information I have gathered on my research for my tank to the more appropriate information of using PAR's.
I would like to know more since in my tank certain plants are thriving as others struggle. Im assuming it is a lighting issue, (or at least light penetration to smaller plants.)
|10-16-2013 01:13 PM|
just needs to change few words to make it right in definition on 1st page:
the radiation (light) that is used by plants for photosynthesis.(means plants absorbed photons)
the radiation (light) that could be used by plants for photosynthesis. (means radiation within specified wavelength)
altho i still might be wrong since English is not my native language
|10-16-2013 11:18 AM|
I prefer a simpler one: One PAR equals one micromole of photons between 400 and 700 nm, radiated from a light source point per second.
|10-16-2013 09:05 AM|
i would like to suggest construction for actual photosynthesis prediction device for diy enthusiasts.
to meet photosynthesis curve we need to divide PAR spectrum in several blocks and adjust each blocks contribution to the summar reading.
easy way to do so looks to me is using different kinds of photoresistors insted of photodiode, because photoresistor itself acts as a filter.
the hard(but more accurate) way would be using several photodiodes with selective filters
|10-16-2013 06:47 AM|
from provided link i read PAR=electromagnetic energy between 400 and 700nm (violet to red) per area unit (often 1 square meter) per time unit (usually 1 second) (and not the actual energy consumed in photosynthesis by plant)
going by this definition you obviously can measure it with relatively simple device.
but then again measuring this way you presume that all wavelengths are equally effectively consumed by plant, which obviously is not true.
still, i do admit this method is better for predicting photosynthesis because it leaves out 'human eye filter curve' introduced in lumen definition.
|10-16-2013 05:11 AM|
"professional" PAR meter sensor spectrum, red line is an "ideal" sensor (in A research defined sense, but I do agree, and the curves make obvious, there is error no matter what you do):
See more here:
See this for my thoughts on a $50 filter/sensor..well more like $70ish, unless you can cut the oversize Baader to use w/ multiple sensors. It is the most expensive part.
silicone photo diode...
Baader filter for UV/IR cutoff
and a inverse filter to Si diode curve
won't be perfect.. but none are..
might as well throw in the expensive Li-cor
Baader filter response:
Si photo diode w/ simulated Baader cutoff applied
|10-15-2013 07:42 PM|
I quote PAR definition in the first post: PAR is an acronym for “photosynthetically active radiation” - the radiation (light) that is used by plants for photosynthesis.
Which basically means that to measure PAR by that definition photosynthesis spectrum curve-like filter is a must on given measuring device. And being microwave engineer I can't imagine how one can produce that filter at home in fifty dollar DIY device.
Simple band pass filter is not good enaugh since it will pass green light which is not used for photosynthesis.
the only thing you guys are actually measuring with your devices is relative light loss in aquarium media. And even that is not completely true since water does not block all wavelengths equally
sorry for being an ass
|10-15-2013 02:43 PM|
|10-15-2013 07:24 AM|
|Master Se7eN||Love it! reason 1 why we need changes.... Wait for it....Wait for it....Here is omes...|
|10-14-2013 11:42 AM|
i still dont get HOW can you build a filter that matches photosynthesis spectrum pattern? without such a filter infront of light sensing element in your meter you are only measuring luminous flux converted via math, nothing more.. actually even worse, you might also be measuring infrared heat that has nothing to do with plant growth
what im saying is if particular device does not have protosynthesis spectrum pattern filter infront of it, i can make it read insane numbers of light that actually cant grow anything. one way is to put it under strong pure green LED. the other way is to put it under near/mid infrared emitter. and so on
|10-14-2013 11:07 AM|
So what do you think I should do with this light configuration ? Should I turn on 4 bulb or with the reflector I have I can go with two than three and at the end 4 bulbs ??
|10-09-2013 12:03 PM|
And this is the shot of my light
Like that you can have an idea.
|10-09-2013 11:19 AM|
thanks for your answer !!
the reflector is a single flat panel of high polished aluminum for the 4 bulbs.
I can see only one image of bulb per real bulb and just at the top of that bulb, so the real bulb cover a bit reflection of this image. So I don't think reflector is doing a great job.
Even if the bulb is half the length of the tank, all the tank is covered by light.
let me search for a pictures of the light and I post it. light is hanging at 20" from the substrate.
Thanks again for your answer and your time.
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