Whenever I wish to talk about light in relation to a planted tank I get pelted with terms like PAR, millimoles, Kelvin, PUR, CRI, LUX, etc. Now I am a hobbyist and not a scientist, I have been gardening from perhaps as soon as I could handle a hoe and keeping planted tanks since my 10th birthday when I received my first tank as a gift; that was nearly 50 years ago. I am not frightened by all those terms but I don’t believe that as a hobbyist, I should invest in PAR-meters, Spectrometers, LUX-meters (they all carry high prices) to choose what lights I would use for my tank; and then having chosen the lights store all those costly instruments in a safe cupboard for the rest of my life.
It is not either that those terms are irrelevant or that I do not understand those terms. All those pertain to measurement of light from the angle of its usage for different purposes. For example:-
PAR - - Photosynthesis Active (Available) Radiation. To find out PAR, light in the 400 nanometer to 700 nanometer range, is measured using a silicon photovoltaic detector in millimoles of light energy per square meter per second. This tells us the energy available at the point of measurement which can be utilised by plants for photosynthesis. As PAR measures energy and not intensity a PAR reading of a pure blue spectrum will give a higher reading than the PAR reading of a pure red spectrum of the same intensity; that is because the shorter wavelength blue light carries more energy than the longer wavelength red light. The fact is that the energy level of light decreases inversely to the wavelength.
Kelvin - - Kelvin colour temperature theoretically should be the visible colour developed by a black body when heated to that temperature on the absolute thermometer (absolute 0º being -273.15°Celcius, and each degree being one degree Celsius apart). At the lowest visible colour temperature the spectrum is red and as the temperature rises progressively shorter wavelengths of visible light are added to the spectrum till finally the spectrum is predominately blue. That’s the theory but in practice the Kelvin colour temperature describing light bulbs are not the Kelvin colour temperature spectrums at all. Modern light bulbs (unlike those ancient incandescent filament bulbs) use either mixtures of phosphor which convert one radiant energy into a mixture of lights of a specific narrow wavelength in the visible spectrum in proportion to the specific phosphor present in the mixture (florescent bulbs); or excite a mixture of gases to give of light in narrow bandwidths peculiar to the mixture of the elements present in the gas mixture of the bulb. The manufactures of these bulbs, with their peculiar spectrums, then approximates the resultant colour of these bulbs to a specific Kelvin colour temperature. You need make an educated guess at exactly what wavelengths of visible light the spectrums of these bulbs contain.
PUR - - Photosynthetically Usable Radiation. Although the entire portion of the PAR can support photosynthesis but some part of this is rendered less useful for green plants; namely because the two chlorophyll pigments, so abundant in green plants, reflects away most of the green-yellow light bandwidth, thereby reducing the utility of this portion of the PAR and makes the remainder PUR, the usable portion. Other pigments which help in harvesting light energy and also the plants with specie particular colouration will also contribute to lowering of the usable portion of the PAR.
CRI - - Colour rendering index. To enable every object viewed to show its true colour; it is essential that that the visible spectrum in which it is viewed should have adequate representation all along its range. The theoretical spectrum at Kelvin colour temperature of 5000 is used as comparison for this index. The measurement as to how close a light bulb can render colour of objects to the 5000K spectrum is the colour rendering index of the bulb. Though many bulbs score above 90% only the incandescent and the halogen have been given a cent per cent 100. Even with that score, only the strongest of incandescent and halogen and that too at glaring high intensity will allow you to distinguish between strands of black, indigo and navy blue threads.
LUX - - LUX is a standardized model of human visual brightness perception which is measured in lumen per square meter using the power at each wavelength of light weighted according to the luminosity function (human eye’s sensitivity to that wavelength) and the sum total being called luminous flux. The human eye has two types of photo receptors on the retina – rods and cones – while the rods are very photosensitive they cannot discern colour; the cones can discern colour but are less photo-responsive. It is because of this that under very dim light we cannot discern colour and our vision sees mostly in black and white and we come up with sayings like “all cats are grey in the dark”. The cones in the retina are three types which respond to three different parts of the visible spectrum, namely in the violet-blue, green-yellow and orange-red. It is the interactions of these photoreceptors in our eye which controls our visual colour perceptions. Under different illuminance levels we have different visual perceptions. These different visual perceptions can be divided into three main modes – Photopic, the way we see in bright light; Scotopic, way we see in low light; and Mesopic, the way we see in intermediary light. Our sense of brightness is mostly controlled by the green-yellow photoreceptors; the other two colour photoreceptors would need five times higher intensity to equal the same sense of brightness. As LUX is the measurement of the sense of brightness we humans perceive and not the power of light, so the different wavelengths have to be weighted separately for this measurement.
My approach to lights for a planted tank is a hobbyist’s practical approach to the problem of correlating two very different aspects – first to grow plants well enough for them to develop naturally and second to be able to see all the inmates of my tank in their true colouration and for that purpose I do not need any of those terms we were talking about.
Plants need light for photosynthesis for the production of all its metabolic requirements; and this production is carried out predominately by the energy gathered from light by its green pigments called chlorophyll. It is well settled fact that these chlorophylls absorb light energy from either ends of the visible spectrum, blue-violet and orange-red. To a much lesser degree plants use other pigments, Carotenoid pigments for example, which also harvest light energy and transfer it for photosynthesis. These other pigments utilise other than the chlorophyll active range of the visible spectrum to gather the light energy. So for photosynthesis we would need a visible spectrum which is high in intensity on the violet-blue and orange-red but not limited to that range only.
Other than photosynthesis plants regulate their growth pattern according to the intensity of the red and far-red part of the spectrum. Low intensity in this range makes some plants stretch and elongate to avoid being shaded out. You get long internodes and straggly growth of stem plants. Strong red to far-red range will give you more compact and bushy plants. It should also be kept in mind that near-violet to blue light regulate a wide range of responses in plants, including phototropism, chloroplast migration and stomatal opening so we should use a spectrum from near violet to far red for the plants with high intensity at violet-blue and red-orange range.
So having ended up with a plant special spectrum which puts an unnatural magenta hue to the tank; we must now do an exercise to tweak it to what will enable us to see the tank inmates in all their true colours. It does not require a lot at all, and we have allies in the tank to help us. We just have to add some light in the green-yellow range which is one-fourth as intense as the violet-blue or the orange-red peaks of our plant special spectrum. Remember this is the range we see five times brighter and also remember our allies in the tank, the plants, they will be reflecting most of it back at us. Now we have a perfect spectrum for our planted tank.
The next question that arises is that how much of this spectrum we need for our planted tank? As far as our own viewing pleasure is considered; we need the light in our tank to be higher than the light of a full tropical moon overhead on a clear night, for though we see quite well to perceive objects under that condition but our colour perception is not good. On the other end we can go as intense as the direct winter sunlight because our spectrum will not produce as much glare that direct sunlight produces.
How much of this spectrum the plants of our tank will need is a little more complicated. Plants like ferns, which have adapted to growing in the shade, can more efficiently use low intensity light to produce enough for their metabolic needs and will survive and grow normally in low light conditions most other plants cannot. Then there are plants like some myrophyllum which given a low light condition will stretch and elongate to make a break for the surface and grow emersed or die trying to do so. Then there are many plants, especially those carpet plants, which just will not survive unless they have much more intense light conditions. So how much of our special spectrum you will need for the plants would depend upon what you intend to grow.
A rolling stone which has come to rest
For those interested in actually calculating/simulating the figures talked about here can turn to my light calculator:
http://www.defblog.se/LightCalculator/
I'm currently investigating if I can manage do a photon map renderer with full caustics that will be able to give more exact numbers.
( @essabee: If you think I'm stalking you it's actually a couple of Google Alerts I have that sends me an email whenever Google is indexing something with PUR usable radiation)
that very interesting calculator. Can you add osram T5HO please? One of the common light tube in this part of the world
I don't mind it at all. In fact I wish I could help you as we are on the same track.Originally Posted by defdac
( @essabee: If you think I'm stalking you it's actually a couple of Google Alerts I have that sends me an email whenever Google is indexing something with PUR usable radiation
A rolling stone which has come to rest
Absolutely, which models are most interesting? 827, 830, 840, 865 or 880? I can add them all but it takes a while to process the spectrums to b&w..Can you add osram T5HO please
Can you add Gro-lux and Aquastar, and would it be possible to have a combination of tubes? I run 1 Gro-lux with 2 Aquastars.
Thanks
I normally use 865 or 880. not sure about availability of other model in Singapore
>"< actually I looked into the internet for halogen, I was wondering why it is so cheap yet no one is using it. So out of curosity, I made a search. -.-" It turn out to be the heat. One of the article said "the heat is so great, a splash of water on a hot bulb can shatter it." I was like "wakaoz! You mean it?!!!" I am now gearing towards more to mh now than T5, currently still using T5..ha ha...I flicker minded again.
Barmby, I used not to be wattage follower. I changed my mind one month after coming back to AQ.But I must be mindful of heat too. Did spray water on light bulbs before when I was young, so I know the effect of heat cracking the bulb vs water. Come to think of it, some forumers have the light hung up, I think that was part of the reason too. I will be more mindful on the lights in future. I was following essabee light setup post too.
It's a neat idea to be able to add different tubes. Shouldn't be too hard to implement. Will see if it comes with the next version. You can add the values until then or just take the value from three Aquastar - you will notice there will not be that much of a difference.Can you add Gro-lux and Aquastar, and would it be possible to have a combination of tubes? I run 1 Gro-lux with 2 Aquastars.
You just want to see in which ballpark you are so to say.
Aquastar is extremely similar to Aquarelle. Both very good tubes regarding getting good growth. I will see if I can hunt down lumens+spectral distributions for these tubes.
It really is one of the most important measures around. Things get freaky when you compare watt/gals between different sizes of tanks since the lit area doesn't vary as much as the volume.To me. Wattage is everything
This means a small tank needs alot more wattage than a big tank.
I will add watt/litre and watt/m2 next version. Then it will be very clear what I just was talking about.
Watts and the conversion by different type of bulbs of that into light are important parameters in comparing bulb output.
Defdac, I use a mix of several types of bulbs in my tanks and would like a system where I could add the results of at least 3 types of bulbs.
A rolling stone which has come to rest
I just setup a standard 3 feet fw tank and still doing its nitrogen cycle in its 2nd week. It won't be a dedicated planted tank, but an aquarium with fish and some plants to beautify it.
What will be the correct T5 tube and the correct wattage that I should use? How many tube(s), will it be just 1 or 2 tubes?
Would really appreciate your advice. Thank you.
Personally I would prefer 3 normal output T5 3-feet long bulbs with individual reflectors and one of the three tubes (the middle one) to be those special magenta coloured bulb and the other two bulbs to be cool daylight (6500K).
If constrained by space to limit my choice to only 2 bulbs; then I would be forced to choose 2 X 3-feet T5 HO (high output) bulb 6500K with individual or combined reflector.
The light would be sufficient for all the easy plants without need for additional CO2.
A rolling stone which has come to rest
Thanks Defdac!
I have somewhere between 3449 and 3997 Lux streaming into my tank. This is about 170 W/m2 or 0.36 W/L (1.4 W/gal). This amount if light is enough to not only grow HM but under the Grolux tube the HM will grow horizontal at a depth of 45 cm. It only grows vertical under the Aquastars at that depth.
Watts are important but light spectrum is also.
Defdac, could you add the specs of the GE Aquarays 9325 K tube.
Thanks
Last edited by TyroneGenade; 16th Feb 2010 at 17:40.
Very true. Bluer high kelvin bulbs tend to grow plants more vertically, and GroLux is the only bulb that makes plant grow with really long internodes that I know of. So it's fairly simple to remember.This amount if light is enough to not only grow HM but under the Grolux tube the HM will grow horizontal at a depth of 45 cm. It only grows vertical under the Aquastars at that depth.
Watts are important but light spectrum is also.
Sure, I will try to find the spectral distribution and lumens/watt specs for it. If someone has a link to this data it's welcome. I will try the GE-site first.could you add the specs of the GE Aquarays 9325 K tube.
Two versions of the GE 9325K is added. The compact 4-pin version is much better than the T8..
Thanks Defdac,
A quick question: the lux which is calculated is the total lux or the percentage lux which is phothosynthetically useful to the plants?
I'm surprised by the low PUR of the GE Aquarays tube. It is supposedly identical to the Triton tube which was all the range a few years back and is still, by modern standards, a good tube for growing plants.
Thanks
Lux is the opposite of photosynthetically useful.
Lux is calculated by adding all the contribution from the lamps spectrum that resides inside the photooptic curve:
As one can see it's almost "the opposite" of the sensitivity of plants and corals since chlorphyll is sensitive to blue and red. Our eye is sensitive to yellow and much less sensitive to blue and red.
PAR adds all frequencies blue to yellow to red. If you get high Lux-values you will get high PAR-values. A PAR-meter is like a glorified Lux-meter with a little more sensitivity to blue and red compared to a Lux-meter. For a blue and red lamp (like GroLux) you will get high PAR-readings but low Lux-readings.
Thus, a measure that only weights the blue and red parts of the spectrum is needed for being able to measure a lamps true photosynthetic power. This is PUR. A PUR-meter will give lamps with high Lux low values, and lamps with much blue and red high values. Within reason. It takes accessory pigments into consideration ofcourse.
Yes, the numbers for the 55 w version have the PUR-efficiency I was expecting. The other one must have been specified wrongly over at the GE-site. It should be just as efficient as Triton, Philips Aquarelle or Sylvania Aquastar. All four are very similarI'm surprised by the low PUR of the GE Aquarays tube. It is supposedly identical to the Triton tube which was all the range a few years back and is still, by modern standards, a good tube for growing plants.
Thks esaabee, can you suggest what will be the wattage if I chose a 2-tube light set for my 3-footer.
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