Fundamentals of Aquatic Lighting

[John P Coates]

Hi Folks,

When we are trying to decide on the suitability of a particular lighting fixture for use in a planted tank including fish, what should we consider? Some of the factors I can think of are as follows:

1 Light spectrum
2 Total light output in PAR
3 Ability to control light intensity
4 Energy efficiency
5 Colour Rendering Index (CRI)
6 Colour temperature (in °K)

Now, what is the relative importance of each - and why?

Thanks.

JPC

 

[ceg4048]

1. Light Spectrum is only a consideration for aesthetic reasons which, due to subjectivity, is not predictable.
2. Total Light output in PAR is the most important factor since this will determine the level of criitcality for CO2/flow/distribution.
3. Ability to control light intensity is the next most important factor based on item #2.
4. Energy efficiency is an economic issues and this therefore depends on the financial status of the hobbyist.
5. CRI is irrelevant and has no value.
6. Color Temperature is irrelevant and has little to no value.

Cheers,

 

[clonitza]

For me is a mix between #1 & #6 for aesthetics, if I like how it renders the color I stick on it, I don't care about something else since I run my tanks with T8s, they are enough to grow any plant and not too much to make my fish wanting to war sunglasses.

Cheers,
Mike

 

[Edvet]

not too much to make my fish wanting to war sunglasses.

 

[John P Coates]

1. Light Spectrum is only a consideration for aesthetic reasons which, due to subjectivity, is not predictable.
2. Total Light output in PAR is the most important factor since this will determine the level of criticality for CO2/flow/distribution.
3. Ability to control light intensity is the next most important factor based on item #2.
4. Energy efficiency is an economic issues and this therefore depends on the financial status of the hobbyist.
5. CRI is irrelevant and has no value.
6. Color Temperature is irrelevant and has little to no value.

Cheers,

Thanks for the feedback.

I cannot understand why you say that the light spectrum is unimportant. This challenges everything I've read on the subject. Since the photosynthetic spectrum clearly shows that plants absorb light mostly in the blue and red parts of the spectrum, it makes sense to me that any light needs to ensure significant radiant energy at these wavelengths.

Surely CRI is very important for aesthetic reasons. If the CRI is low, say 30%, the plants and fish will take on a non-lifelike hue. Colour temperature will have a similar effect. If the lighting is 'warm', say 2700°K, the tank and its contents will look as though it is being illuminated by incandescent bulbs. Not exactly representative of the natural light seen by tropical plants and fish.

JPC

 

[GlassWalker]

The light spectrum feeds into CRI and colour temperature, so they're kinda related. In essence the spectrum is the raw data, and the other two are numbers calculated from it. In my experience, colour temperature only seems to work where it is in the ball park of sunlight. It doesn't seem to work so well at very high values e.g. the tubes provided as standard with a Fluval Roma are rated at 18000k each but to me seem a fairly balanced white, not as blue as its value may suggest. I would also caution the colour temperature is a single axis, whereas you need at least two to describe colour. So it also falls down with unbalanced light spectrums. For example, the Interpet Tropical Daylight tube I find has a pink hue to it I don't like, and one of the Narva tubes is rather yellow-green strong which I don't like either. CRI is an imperfect measure of how filled out a spectrum is. Generally I find higher CRI ones look better, but recognise that is subjective.

I think efficiency has a contributing factor to running an aquarium. If the lighting produces a lot of heat, then depending on the aquarium design that heat may cause problems with water temperature. In the recent warm weather I'm glad I binned my T5s and T8s, and moved almost everything to LED now as I get comparable light output at much lower heat generation.

A question for all about PAR - Given the peak responses of chlorophyll in the red/blue regions of the spectrum, would a better measure not be to weight the measurement in those areas? E.g. if you had 1 unit of light in the green region, would that not grow plants slower than 1 unit total of a red/blue mix, assuming nothing else is limiting? This then ties in with efficiency. Taken to an extreme there are those red/blue lights used in hydroponics, but look really unnatural.

I'll also throw in another question about spectrum while I'm here. I vaguely recall reading in multiple places about how plant growth can change depending on the balance of red/blue light. I can't recall which way around it was, but biasing to one was claimed to increased growth, and biasing the other way encourages flowering/fruiting. I didn't look into this further at the time. Any comments on this?

 

[Edvet]

I know it's hard to let go off years of indoctrinating lighting spectrum, colour and CRI matter. It doesn't. There is more then enough energy in the foton's to use for the plants, they don't care about all these things. PAR is the king.
You can choose to not believe this, in that case i have some prime building grounds for sale in South america.................., or the Eifel tower for a reasonable deal..............

 

[GlassWalker]

I can see how PAR might work within certain limits and assumptions, but a better measure would reduce those uncertainties. Likewise with the colour temperature. Of course, you're welcome to say you don't need a better measurement for those, and what we have now is good enough. When I get interested in things, I like to know how everything works, even if it isn't necessary to function. It is likely I'm entering the region of diminishing gains for the effort expended. When I have time, I have some possible improvements to suggest on EI for example... although they depend on the validity of certain assumptions related to the process, but will save that for another thread.

 

[John P Coates]

I'll also throw in another question about spectrum while I'm here. I vaguely recall reading in multiple places about how plant growth can change depending on the balance of red/blue light. I can't recall which way around it was, but biasing to one was claimed to increased growth, and biasing the other way encourages flowering/fruiting. I didn't look into this further at the time. Any comments on this?

Hi GW,

Many thanks for your reply.

I have singled out one point you raised above.

Yes, I have also read about this. My recollection is that blue light encourages leaf growth whereas red light is important for fruiting. Chances are that I read about this in connection with horticulture rather than aquatic plants. I'll see if I can find a link. NASA were the first to show that potatoes could be successfully grown under a combination of blue and red LEDs. They wanted to see how to feed astronauts on board the ISS. Must be a welcome change after those pouches with attached straw!

JPC

 

[Edvet]

http://www.ukaps.org/forum/threads/spectrum-doesnt-matter-does-it.26717/

 

[John P Coates]

I know it's hard to let go off years of indoctrinating lighting spectrum, colour and CRI matter. It doesn't. There is more then enough energy in the foton's to use for the plants, they don't care about all these things. PAR is the king.
You can choose to not believe this, in that case i have some prime building grounds for sale in South america.................., or the Eifel tower for a reasonable deal..............

Edvet,

Please substantiate your statements about lighting.

I fail to understand the relevance of your references to South America and the Eiffel Tower.

JPC

 

[James O]

Please substantiate your statements about lighting.

For informed debate, and as you raised the subject, please substantiate yours first (alternatively, please use the search function) Edit: or even easier now as the link has been posted

I fail to understand the relevance of your references to South America and the Eiffel Tower

Humor fail

Don't worry though its all above board. I took Edvet up on another offer and now own a lovely plot in Columbia and two amazing sculptures. One a darling statue of a woman holding a flaming torch aloft and the other is of the Christ with his arms outstretched. Its a shame he's so wide though as postage from South America now seems to be an issue

 

[ceg4048]

Worrying about spectrum is really a waste of time and energy. What is demonstrated in a laboratory does not always translate to real world. There are many factors that have an effect on plant growth and health and each factor has a different magnitude of impact. As a result of aesthetics, subjectivity, art as well as the lighting industry itself, whatever advantages/disadvantages occur as a result of spectral distribution variation, these are obliterated by the orders of magnitude differences that result from the other factors in plant husbandry, such as, for example, flow/distribution/CO2 and PAR, which make about a 1000X difference to plant health than spectral distribution could ever dream of doing. Additionally, attempting to manage spectral distribution would be a complicated affair. Therefore, since the benefits of controlling spectrum is extremely low, while at the same time it's execution is very complicated, there is no point in taking this path because the path leads nowhere. We can grow excellent plants using any spectrum we want, and no one can declare, with any validity that the results of applying one spectrum is any better than the results of applying any other.

Color is an invention of the human mind only, therefore, parameters such as Color Rendering Index have no meaning in this application because one persons invention may not satisfy anothers. No one really cares if colors are accurate. The colors must be pleasing. Accurate and pleasing are mutually exclusive when it comes to art. Arguing about what color is more accurate or is better suited to plants is like arguing about what ice cream brand has more accurate or better flavor. Truly pointless unless the subject is fashion photography or crime scene forensic investigation.

The hobby is complicated enough and there are enough things to worry about without complicating life further with things that don't matter.

Cheers,

 

[clonitza]

There is more then enough energy in the foton's to use for the plants, they don't care about all these things. PAR is the king.

Neither, the optimal light was "researched" a long time ago .. the old t8 tubes setup provide(d) everything that is(was) needed.
Later on the producers decided that this approach wasn't beneficial for their big pockets and threw in t5s, mhs and now leds.
If algae had been traded on stock it would've bitten gold 10 times.

 

[James O]

True true, but now I can have much more control over multiple LED's now. Thats the difference

We had all the light we need. Now we have the light we want - Nothing at all to do with plant health

1) Get some lights (not too much mind you)
2) Get on with it
3) Stop worrying about it

 

[John P Coates]

It's a shame that one cannot ask a simple question on this forum without being either ridiculed or attacked in some way. I have never experienced this on any of the other forums that I regularly use. My participation in this community can only decline.

JPC

 

[BigTom]

It's a shame that one cannot ask a simple question on this forum without being either ridiculed or attacked in some way. I have never experienced this on any of the other forums that I regularly use. My participation in this community can only decline.

JPC

Hi John,

I don't think anyone in this thread has intended to attack or ridicule you. Advice/discussion on here can be somewhat on the 'robust' side, but very rarely is it personal. Oh, and Edvet is Dutch, they can find humour difficult sometimes (I know, my better half is Dutch).

 

[GlassWalker]

Thanks for the link to the previous thread on this subject. I'll have to have a more in depth read when I have more time. I'm not surprised the original question has come up before, but finding such content is another matter. This forum doesn't seem to be organised with topic FAQs as such. If these could be added, even if only linking to past threads, I think that would be helpful for relative newcomers like myself.

I'll also further add at this point, my goal is not to the best planted tank, but to understand the factors involved however small. The side effect should be I have a good planted tank in due course, but that is not my goal in itself.

 

[Edvet]

Now who's sleeping on the couch tonight........

they can find humour difficult sometimes

 

[James O]

Oh, and Edvet is Dutch, they can find humour difficult sometimes

Oh hell! Does anyone want to split the statue of liberty with me or go halves on a timeshare in Columbia?


If you come to a question, don't post it - search it, under multiple phrases first. You'll likely always get comedy or short replies if the answer already exists and someone has to constantly repeat themselves