Toward a standard understanding of aquarium lighting

[DeeDeeK]

I meant you also have to consider additional pigments such as xanthophyll and carotene which are designed to absorb wavelengths different from the chlorophylls.

Naturally. It's just my style to read something I could read two ways the wrong way.

Here's a couple of graphs I found online which may be relevant.

The lower graph, of Anachris sp. relative rates of photosynthesis by wavelength, shows a curve(s) that could be used to weight the measurement of emitted visible light by its relevancy to photosynthesis. Naturally, plants with different proportions of various photosynthetic pigments will have different levels in their graphs but several common species' figures could be averaged to make quite a useful guide.

If one were to sample the intensity of a lightsource of every wavelength between 400 nm and 700 nm at 1 nm intervals, and multiply it by the value given for "relative rate of photosynthesis," in the above graph, then average all those results, one would have a number which says something useful about the photosynthetic response which can be expected.

A composite graph of several species, as I've described, could be generated from several species and applied uniformly to various light sources. Then one could tell at a glance the power of a tube or bulb or LED as it relates to plant growth - no worries about actual spectrum or wattage. Wattage and any other information would and could still be included on the packaging or printed on the glass or plastic. That way, within the rated wattage of the fixture, one would have a better sense of their range of choices in light source and not necessarily feel constrained to a narrow range of perhaps inappropriate (for that particular aquarist) choices.

Since even green light is a little useful, about a 1/3rd as useful as blue is, we might find that a cool white or even warm white light of a certain power is all we need. Or we might have to really focus on those reds and blues in order to get sufficient useful light to the aquarium due to, say, space constraints or power constraints. Or possibly we like the bleachy-blue-white spectrum of a 10000k PC tube and find that our plants will do just fine in its spectrum. Ok, last one, we may find a nice looking 5500k PC tube and discover it has a disappointingly low rating; when we get a look at it lit though, we can see how strongly green its spectrum is with our own eyes when we compare a white sheet of paper under its light with the light of another source.

Yeah, there are "daylight" balance bulbs in the 5500k neighborhood which are largely green. Loads of green will weigh a light's spectrum toward a higher kelvin rating even if the blues aren't really strong.

 

[JamieB]

WoW! You sure know your stuff when it comes to lighting, thanks for all the time an effort you used to put together this informtion to inform us on this very interesting topic in the fish keeping hobby.opcorn:

 

[DeeDeeK]

WoW! You sure know your stuff when it comes to lighting, thanks for all the time an effort you used to put together this informtion to inform us on this very interesting topic in the fish keeping hobby.opcorn:

No kiddin'? Thanks. I learn a lot when I start a discussion about something I know little about. Being challenged by feedback pushes me to look up and research the terms used by everyone else, like PAR, which I did not know prior to reading it in this thread.

Also, I like to be a gadfly and stir up some discussion...

 

[Aphotic Phoenix]

I just wanted to show visually why going by "lumen" can be a huge waste of time:


This bulb would appear very bright, and should have a high lumen rating...yet it has very little going for it in regards to maximizing plant growth. Yes, I know we've already established this...I just felt this post need more visual aides.

Really however, the most significant factor for plant growth has much less to do with lighting, and much more to do with available CO2 and nutrients ala Tom Barr. (Seriously, if you haven't looked up his work do it now.) He runs some stunning tanks with very moderate lighting.

As for the difficulty of lighting a small aquarium well...LED's or T2's (depending on your budget) should help with that significantly. An individual reflector for 1 T2 bulb would potentially be under an inch in width, which should leave plenty of space for multiples. XD

 

[DeeDeeK]

I just wanted to show visually why going by "lumen" can be a huge waste of time:

View attachment 123364
This bulb would appear very bright, and should have a high lumen rating...yet it has very little going for it in regards to maximizing plant growth. Yes, I know we've already established this...I just felt this post need more visual aides.

Really however, the most significant factor for plant growth has much less to do with lighting, and much more to do with available CO2 and nutrients ala Tom Barr. (Seriously, if you haven't looked up his work do it now.) He runs some stunning tanks with very moderate lighting.

As for the difficulty of lighting a small aquarium well...LED's or T2's (depending on your budget) should help with that significantly. An individual reflector for 1 T2 bulb would potentially be under an inch in width, which should leave plenty of space for multiples. XD

Thanks!

The Barr Report is great. Read up there on Estimative Index to see a handy tool for the more involved hobbyist.http://www.barrreport.com/forum.php

That graph showing the heavy emphasis on green wavelengths is perfect. The envelope used for weighting the measurements used arrive at a figure for lumens is almost the inverse of the one showing the photosynthetic response of Anachris sp. to frequency.

Here's a link to an article I found which explains a lot of terms like lux, lumens, illuminance, etc., and has a nice graph showing the retina's sensitivity to different frequencies of light.http://reefkeeping.com/issues/2006-04/sj/index.php.

The green curve is pretty much the envelope used to weight the measurement of light to arrive at lumens.

One term I almost like is "illuminance." Illuminance is the incident light on a surface, formerly called brightness, measured in lumens/square meter. My interest in lighting has been to give one a measure of control in how "bright," as measured by photosynthetic activity rather than human vision, it actually is at a given level in the aquarium (for example, the bottom).

As for lighting the small aquarium, I would prefer a nice, even, distribution of light within it and while T2's and LEDs might produce plenty of light, nearby light from a small source provides uneven coverage. I'd like to replace my hood with glass or plexiglass and hang a powerful lamp high enough above it that the light is very evenly spread throughout the volume of the tank. I have another tank which is well lit at the bottom but the light source is small enough that at the top, it really only lights like 1/3rd of the surface at the very best. The plants all grow toward the light, so those at the edges are definitely NOT vertical. I'd like to hang a light above that one high enough that the plants would grow more or less vertically OR set up a bank of smaller, weaker lights which would give even coverage. The single, higher lamp would be cheaper and easier.

If there were a simple figure on the bulb/tube/LED I could read which would give me an idea of how high up I could suspend it for my purposes, this would project would be a snap. I'd go for the lowest wattage light source with adequate PUR. As is, I can guess based on wattage, color temperature, advertised spectrum (like Vita-Lite, which is sorta close to the solar spectrum).

So, let's say I've a 5 gallon tank to light. I find that hanging a reflector/light combo at 2.5 feet above it gives me the spread of light I want. How bright should the light source be? 3wpg? 15 watts from 3'2" from the floor of the tank? 10 wpg? Let's say wpg is actually a useful measure, but but from what distance? 21" - the height of a standard 55 gallon tank? If so, what does 1 wpg at 21" mean at 38"?

Let's say I've got a measurement on my light that says it puts out one arbitrary unit of photosynthetically useful radiation (1 PUR) at 20" and I want 1 PUR at the bottom of my 10" deep tank BUT I want to hang the light 40" up to achieve a really smooth spread. How many lights do I need? Four.

If PUR =1 at 20" then PUR = 0.25 at 40." If the distance were 10" the PUR would equal 4. It works like this: The PUR level measured at one distance will be that level x 1/ ((new distance/old distance)squared) at the new distance. in a calculator, enter the new distance from the light source, hit the divide key, enter the old distance then hit enter or equals then hit multiply then equals then M+ then hit 1, then divide, then MR then equals.

To figure PUR at 30" from a known measurement of PUR at 20":
PUR = PUR x 1/(30/20)x(30/20)
30/20 = 1.5
1.5x1.5= 2.25
1/2.25 = .4444444
PUR at 30" = PUR at 20" x.4444444
So at 30", PUR will be approximately 44.4% the strength it would be at 20"

 

[pongo]

wow, just when I thought my brain wasn't getting enough exercise here comes one of several posts by DDK. I love them!! Great responses by AP also.

 

[DeeDeeK]

Really however, the most significant factor for plant growth has much less to do with lighting, and much more to do with available CO2 and nutrients ala Tom Barr. (Seriously, if you haven't looked up his work do it now.) He runs some stunning tanks with very moderate lighting.XD

Well, I agree and disagree. I disagree because that there be adequate lighting is essential - if a plant can grow at it's maximum rate with minimum of x amount of light and x amount of ferts, CO2, etc., it will grow less quickly if there is less than the minimum needed for greatest growth. And if there isn't the minimum lighting needed for growth at all, well we all know a plant needs light for heaven's sakes. I agree in a way because it's pretty easy in many cases to provide enough light for good growth, and we don't really need to approach the theoretical maximum potential for plant growth in most cases.

In any case, there are more issues than simply that there be enough light for good growth and lush tanks. There is the spread of the light, the direction(s) phototropic plants grow in, the color rendering, could we make the tank brighter without actually boosting growth? If filtration were just a matter of removing particles, NH3/NH4, NO2, and using a little carbon to suck up organics, we would have no need for anything but a HOB filter and some pre-packaged cartridges or maybe an UGF with carbon carts. However, creativity has demanded more and so we have a proliferation of means of filtration and biofiltration.

I simply say creativity demands more useful tools and understanding for dealing with light. WPG is barely functional - it doesn't function for more than the bare necessities and not always that well.

 

[DeeDeeK]

wow, just when I thought my brain wasn't getting enough exercise here comes one of several posts by DDK. I love them!! Great responses by AP also.

YES! AP, thank you!

 

[Aphotic Phoenix]

I agree in a way because it's pretty easy in many cases to provide enough light for good growth, and we don't really need to approach the theoretical maximum potential for plant growth in most cases.

This was what I was pretty much getting at. It's completely possible to provide enough, and even too much light (in terms of potential algae problems)...it's finding the most efficient combination possible that is difficult.

There is the spread of the light, the direction(s) phototropic plants grow in, the color rendering, could we make the tank brighter without actually boosting growth?

Light spread can also be somewhat affected by lenses (LEDs), and reflector type (FL). The directional focus of LED's actually has a bit of an advantage in that it should lose a very minimal light to restrike. The effiencey of light out put from FL can be strongly impacted by the type (or lack there of) of reflectors used. Bulbs with individual parabolic reflectors minimize light lost to restrike. This is why it's useful to know the limitations of individual light types. A T5 with a good individual reflector could be calculated at 1.5X the light output of a T8 for example.

In terms of plant growth direction...plants are actually perfectly capable of correcting themselves (for the most part). Haphazardly plant some Brazilian Pennywort in a tank, and by the next day it will have the majority of it's leaves facing the light.

If filtration were just a matter of removing particles, NH3/NH4, NO2, and using a little carbon to suck up organics, we would have no need for anything but a HOB filter and some pre-packaged cartridges or maybe an UGF with carbon carts. However, creativity has demanded more and so we have a proliferation of means of filtration and biofiltration.

HOB's pose two problems in terms of planted aquaria:
1. They have a strong potential to gas off the CO2 we want for our plants.
2. They provide poor circulatory flow, and thus poor distribution of nutrients.
Cannister filters, although not truly necessary, provide a lot more control over current, more options in delivery (such as lilly pipes), ability to install CO2 reactors and inline heaters, etc. Powerheads do offer a great way to supplement current however.

I simply say creativity demands more useful tools and understanding for dealing with light. WPG is barely functional - it doesn't function for more than the bare necessities and not always that well.

I certainly don't disagree with you on this, but the complexities of dealing with the variables in vast array of equipment choices out there make formulation of simple guidelines difficult.

Thanks guys. I'm sorry that I can't be more useful. XD It's been awhile since I've done serious research on aquarium lighting, so I'm a little rusty.

 

[katana1200]

Something back there, way back there, in a place I haven't used much since high school, just popped a bit. Sounded like a rusty gate hinge inside my head. I think it hurt a little. Thanks a lot guys, now I need a nap. My fish said they like my lights just fine and my plants are all still alive so my lumins, purs, pars, watts, megahurtz, and nanometers must all be ok....I hope.

All joking aside, very informative thread. Going into my bookmarks for more in depth research later. Thank you for the information.