# Do t8 lights really degrade over time?



## terry82517 (19 Jan 2013)

Hi all, I have 2x 30 watt t8 bulbs in my rio 180, co2, ei dosed planted tank, have had the bulbs for longer then I can remember and I'm thinking of replacing them as I've read that they lose their power after a year or so. Is this true or some another ploy to get you to buy new bulbs all the time?


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## foxfish (19 Jan 2013)

You will hear different opinions about this, personally I think they do produce less light over time & change mine as a matter of course every year.
If your plants are growing well then the only reason to buy new would be for a fresh colour but, if you do I would only change one at a time just in case they are much brighter, you dont want to encourage algae growth with to much light!


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## BigTom (19 Jan 2013)

I think I remember seeing a graph somewhere that showed that they do degrade, but only by a few percent. I could have dreamt that however! I'm sure someone will be bale to provide a better answer.


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## ceg4048 (19 Jan 2013)

terry82517 said:


> Is this true or some another ploy to get you to buy new bulbs all the time?


 Yes it's another ploy. It doesn't matter one iota if the bulbs lose some of their PAR output. The plants will adapt and increase their absorption efficiency. And people use way too much PAR to begin with, so it's actually a good thing if the bulbs drop their output.

Cheers,


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## Pelagio (20 Jan 2013)

It depends whether your tank is set up to rely on higher lighting levels too.  I cannot believe that if  a tank is running well on a certain level of light, and that light level degrades over time, that you will achieve the same results.  I see what CEG means about the plants adapting, but surely that means they would grow slower ?  That would not bother many people mind you.  (Though I am quite pleased how quick my Pogostemon and Rotala is growing at the moment as I cant afford to buy extra plants to fill out the gaps they are filling hehe).


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## foxfish (20 Jan 2013)

Depends on what you imply by 'the same results'?
We all know that C02 is the governing factor & light is used to match the gas supply, so if the light lessens over time & the gas remains at the same level the most likely even will be an overall cleaner tank.
I mean the plants will be healthy & the chance of algae decreased, probably resulting in not even a hint of algae, so yes there will be different results but necessary for the worst!
If you mean plant growth will be slower with less light then possibly yes but not necessarily by much!


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## Pelagio (20 Jan 2013)

foxfish said:


> Depends on what you imply by 'the same results'?
> We all know that C02 is the governing factor & light is used to match the gas supply, so if the light lessens over time & the gas remains at the same level the most likely even will be an overall cleaner tank.
> I mean the plants will be healthy & the chance of algae decreased, probably resulting in not even a hint of algae, so yes there will be different results but necessary for the worst!
> If you mean plant growth will be slower with less light then possibly yes but not necessarily by much!


 

Hi foxfish, yes i was referring to plant growth rate primarily.  You say not necessarily by much. Are there any studies that can give actual figures on this ? Its an interesting topic.  For example, if say my lighting levels were reduced by 50% output due to tube degradation would that be reflected by a 50% reduction in growth rate ?  If so, I can imagine some people not being prepared to wear that (especially when many want their scapes to grow in relatively quicky for competition images).  But if it would only be reflected by say a 5% reduction then it would not matter as much.


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## ceg4048 (20 Jan 2013)

Hi,
	First of all it's not really a good idea to rely on higher lighting levels because light only has a positive effect on growth rate, not on plant health. In fact, just the opposite. Those who rely on high lighting almost invariably suffer plant health related issues. In any case, you will not be able to detect the reduction of growth rate because it isn't significant. There is a much higher affect on growth simply due to CO2 tweaking or due to nutrient concentration levels. You said it yourself. If you are satisfied with the growth rates why spend more money to get new bulbs?

Have a look at a thread regarding old bulbs. The thread discusses T5, but exactly the same applies to T8. Two new tubes... | UK Aquatic Plant Society

Cheers,


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## Ady34 (20 Jan 2013)

Hi Terry,
one thing to consider is that if you introduce new bulb/bulbs, you may need to increase carbon availability slightly again to compensate for increased par. The plants will have got 'hooked' on the current co2 and when trying to increase growth rates due to the increase in lighting imtensity could lead to issues. If the co2 is maxed regards fauna, liquid carbon is a good booster.
Alternatively you could decommission any reflectors if used or add extra floating plant cover. As Foxfish said, it may be a good idea to add one bulb at a time to reduce any ill effects.
Cheerio,
Ady


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## Pelagio (20 Jan 2013)

ceg4048 said:


> Hi,
> First of all it's not really a good idea to rely on higher lighting levels because light only has a positive effect growth rate, not on plant health. In fact, just the opposite. Those who rely on high lighting almost invariably suffer plant health related issues. In any case, you will not be able to detect the reduction of growth rate because it isn't significant. There is a much higher affect on growth simply due to CO2 tweaking or due to nutrient concentration levels. You said it yourself. If you are satisfied with the growth rates why spend more money to get new bulbs?
> 
> Have a look at a thread regarding old bulbs. The thread discusses T5, but exactly the same applies to T8. Two new tubes... | UK Aquatic Plant Society
> ...


 

Hi ceg, so you are basically saying that a large reduction in lighting output only results in an insignificant reduction in growth rate ? Im trying ot get my head around this as so many people seem to want higher and higher light levels.  George Farmer has just set up a small tank with two whopping great TMC led's above it.  I know that he can adjust the output of them as well as the height if they were not adjustable but it begs the question "whats the point".  Are we getting conned by all the LED manufacturers, only in a different way to the flouro tube manufacturers telling us to replace our tubes every 6 months ?


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## Ady34 (20 Jan 2013)

Pelagio said:


> Hi ceg, so you are basically saying that a large reduction in lighting output only results in an insignificant reduction in growth rate ? Im trying ot get my head around this as so many people seem to want higher and higher light levels.  George Farmer has just set up a small tank with two whopping great TMC led's above it.  I know that he can adjust the output of them as well as the height if they were not adjustable but it begs the question "whats the point".  Are we getting conned by all the LED manufacturers, only in a different way to the flouro tube manufacturers telling us to replace our tubes every 6 months ?


For many I believe the led route is a lot to do with aesthetics and minimisation, plus as you suggest you have the control element which is great for a more natural light build up and reduction to assimilate nature. With this you also have a greater level of control over co2 introduction.


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## foxfish (20 Jan 2013)

LEDs also have a lot to do with the whole hobby scene, folk like to be involved with their tanks & equipment & spend money on the latest kit - nothing wrong with that in my mind 
It is a bit like the original question....it might or might not be necessary to change the bulbs but, I change mine every year because I want to!
There is more than one way to skin a cat,  you can use hight light to grow plants fast, take a look at some of the American forums, those guys are crazy for light but you can also grow plants with low light & that seems to be the more effective overall method at this present time!
It is difficult to predict the future & perhaps views & techniques will change before long, however I am personally having great success with a short lighting period & less than 2 watts per gallon.
The thing is..... I kind of miss my mega watts tanks, I want to go fast on my motobike, I want to run faster than I ever have & I want mega watts on my tank LOL


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## Pelagio (20 Jan 2013)

Ady34 said:


> For many I believe the led route is a lot to do with aesthetics and minimisation, plus as you suggest you have the control element which is great for a more natural light build up and reduction to assimilate nature. With this you also have a greater level of control over co2 introduction.


 
I think you are probably right.  Best of both worlds then


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## BigTom (20 Jan 2013)

Found this graph after a bit of a google - you can see that T8s never lose more than about 10% of their output, and that's after about 3 years of use (assuming 3500 hours a year if used for 10 hours/day in an aquarium). So I really wouldn't worry about changing them.

T5 and T5HO lose even less (about 5% of their output over their lifetime).

Halides do decay somewhat more significantly, but Clive's arguments still apply.


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## terry82517 (20 Jan 2013)

My lights came with the tank when I brought it second hand so god knows how old they are, have nothing to compare growth to as they are all iv had! 

But the general consensus is only bother replace when bulbs stop working or blow I guess?


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## Tim Harrison (28 Jan 2013)

Yes...but can you grow carpet plants like glosso with decaying T8s?

Lets face it to provide the optimum growth conditions for high light plants you need quality over quantity. In other words high light in combo with optimized ferts, flow, and CO2...oh and timing...everything always comes down to timing, it's a rare universal constant.

The artistry is in getting the balance right, which isn't easy for the uninitiated - which I'm guessing is Clive's big frustration - lighting is not a panacea in itself.

George has two whopping great TMC led's because he understands this fundamental universal truth...he has more than an inkling how to balance stuff!


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## BigTom (28 Jan 2013)

Troi said:


> Yes...but can you grow carpet plants like glosso with decaying T8s?
> 
> Lets face it to provide the optimum growth conditions for high light plants you need quality over quantity. In other words high light in combo with optimized ferts, flow, and CO2...oh and timing...everything always comes down to timing, it's a rare universal constant.
> 
> ...


 
Confusing the point a little I think Troi - you'd stand pretty much the same chance using 5 year old T8s as you would brand new ones.


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## Tim Harrison (28 Jan 2013)

What? can you or can't you grow glosso under T8s?
I think like you, I'm not convinced you can (that is in the form of a dense carpet) and T8s do degrade quite markedly - IMO - over the period of a year or so; and that is kinda of the point in itself...but not all...

...all this talk about plants adapting to lighting conditions is all well and good but there still has to be an optimum for photosynthesis, especially for light demanding plants like glosso . And this may be controversial, but I think the spectrum has more to do with that than mere aesthetics.

But nevertheless, I think the point I'm trying to make is that light is just another nutrient and if other factors are not optimized - whopping great TMC's aside - Liebigs Law of the Minimum applies. Or am I still missing the point...I never know these days.


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## BigTom (29 Jan 2013)

Troi said:


> What? can you or can't you grow glosso under T8s?
> I think like you, I'm not convinced you can (that is in the form of a dense carpet) and T8s do degrade quite markedly - IMO - over the period of a year or so; and that is kinda of the point in itself...but not all...


 
I have no idea, I've never tried. But the evidence is that T8s only degrade 5-10% over their lifetime, and I doubt that makes much difference one way or the other. If you've got evidence that they degrade more than that it'd be good to see, I'm just relying on a bit of googling.


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## foxfish (29 Jan 2013)

I am pretty sure that George himself wrote about how he found the par rating diminished considerably over a quite sort time!
I might be wrong but I think there was even an article in PFC by George ?
Anyway if you are old enought to remember when every house was powered by fluorescent tubes - then you will remember that they do in fact lose brightness!


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## ceg4048 (29 Jan 2013)

Light is not a nutrient and therefore there is no such thing as "optimum light". The function of light is to supply quantum energy packets. The role of the chlorophyll molecule and other pigment molecules is to convert quantum energy to electro-chemical energy. Photon absorption results in a change in the energy state of the valence electron in the pigment. This energy state change powers those reactions that assimilate nutrients which are themselves elements.

Light therefore is analogous to a battery, or a generator, so there is no such thing as optimum value. There are only "minima" or "maxima". The more voltage supplied by the batteries or generator to a system,  the more assimilation can occur.

It is this fundamental misconception of light that causes all the trouble, and it is exactly why folks struggle.

Cheers,


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## ian_m (29 Jan 2013)

terry82517 said:


> Hi all, I have 2x 30 watt t8 bulbs in my rio 180, co2, ei dosed planted tank, have had the bulbs for longer then I can remember and I'm thinking of replacing them as I've read that they lose their power after a year or so. Is this true or some another ploy to get you to buy new bulbs all the time?


You guys have obviously not used Juwel T8 tubes, which seriously drop off in light output after a year. Might be cheap at £6 odd each from LFS, but the £20 Arcadias I bought are still beaming bright a year later. Recently whilst tidying garage came across the year old Juwel tubes and tested them in my light fixture, the difference in light output between year old Arcadia and Juwel is amazing. Got to keep at least one Juwel tube though as spare, as the Juwel lighting units require two working tubes, wont work with just one, so if eventually an Arcadia tube fails I can just put in a Juwel tube whilst getting a replacement.


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## dw1305 (29 Jan 2013)

Hi all,


foxfish said:


> Anyway if you are old enought to remember when every house was powered by fluorescent tubes - then you will remember that they do in fact lose brightness!


This was true, but is only relevant for non-electronically ballasted, non-triphosphate tubes, these were the ones that use to buzz and cycle at the end of their life.



BigTom said:


> But the evidence is that T8s only degrade 5-10% over their lifetime, and I doubt that makes much difference one way or the other. If you've got evidence that they degrade more than that it'd be good to see, I'm just relying on a bit of googling


 
Tom is right all modern fluorescent tubes and fittings show all most no "lamp lumen depreciation" until they fail.
<Do T5 lamps have better lumen maintenance than T8 or T12 lamps? | What are T5 Lamps? | T5 Fluorescent Systems | Lighting Answers | NLPIP>

I've mucked about with a lux meter, and this is definitely true for lux (using T5 under-cabinet lights), but I don't have a PAR meter.  The main problem with the link lights has been that the plastic photo-degrades really rapidly.

cheers Darrel


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## ceg4048 (29 Jan 2013)

Yeah, unless you measure PAR directly, whether Juwel bulbs or otherwise you cannot really draw a conclusion regarding the falloff. Plants do not care about Lumens, they only care about PAR. So, if the bulb has a spectrum shift away from green and yellow and towards red for example, then to human eyes, they will look much dimmer than their actual PAR loss. The charts presented in this thread all show Lumen degradation which is not relevant. So there might actually be a significant PAR loss with Juwel but you cannot determine that from any of those charts.

Cheers,


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## BigTom (29 Jan 2013)

ceg4048 said:


> Yeah, unless you measure PAR directly, whether Juwel bulbs or otherwise you cannot really draw a conclusion regarding the falloff. Plants do not care about Lumens, they only care about PAR. So, if the bulb has a spectrum shift away from green and yellow and towards red for example, then to human eyes, they will look much dimmer than their actual PAR loss. The charts presented in this thread all show Lumen degradation which is not relevant. So there might actually be a significant PAR loss with Juwel but you cannot determine that from any of those charts.
> 
> Cheers,


 
Good points. Wish someone with too much time and money on their hands would quantify this sort of thing


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## dw1305 (29 Jan 2013)

Hi all,


ceg4048 said:


> Yeah, unless you measure PAR directly, whether Juwel bulbs or otherwise you cannot really draw a conclusion regarding the falloff.


I'm trying to persuade work to buy me a PAR meter, but I'd put money on it that is either the Juwel tubes have halo-phosphate phosphor coating and/or they are magnetically ballasted.

As the T8 Juwel tubes are a funny size (I think?), I'd put my money on halo-phosphate coating.

cheers Darrel


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## ian_m (29 Jan 2013)

dw1305 said:


> Hi all,
> As the T8 Juwel tubes are a funny size (I think?), I'd put my money on halo-phosphate coating.
> cheers Darrel


Standard T8 25W 2 1/2 foot size, running from electronic ballast.

Alternatives are available all over the place. I used a "standard" white tube (only £3 odd) from www.tlc-direct.co.uk for a while, but was too yellow for my liking.


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## dw1305 (29 Jan 2013)

Hi all,


ian_m said:


> Standard T8 25W 2 1/2 foot size, running from electronic ballast.


S*d, thanks for that, I was on a roll with strange length halo-phosphate tubes, until the cold hard truth intervened. I don't know the answer then. It will have to wait for the PAR meter.

cheers Darrel


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## Tim Harrison (30 Jan 2013)

ceg4048 said:


> Light is not a nutrient and therefore there is no such thing as "optimum light". The function of light is to supply quantum energy packets. The role of the chlorophyll molecule and other pigment molecules is to convert quantum energy to electro-chemical energy. Photon absorption results in a change in the energy state of the valence electron in the pigment. This energy state change powers those reactions that assimilate nutrients which are themselves elements.
> 
> Light therefore is analogous to a battery, or a generator, so there is no such thing as optimum value. There are only "minima" or "maxima". The more voltage supplied by the batteries or generator to a system, the more assimilation can occur.
> 
> ...


 
Thanks Clive

With regards to light as a nutrient - perhaps I need to qualify what I meant. I was alluding to the importance of attaining a healthy equilibrium to achieve optimum plant growth. In this respect it’s sometimes easier to consider light as a nutrient, in general terms, in that its intensity drives the rate of photosynthesis along with temperature, actual nutrient availability and CO2. In any given situation anyone of these can become a limiting factor; hence my use of Liebig’s Law of the Minimum as an analogy.

But I understand that there is much more to growing plants than light intensity and so by using the phrase optimum light I was alluding to maximizing PAR, particularly the blue and red spectral range which chlorophyll is the most efficient at absorbing: which after all is the reason why PAR is preferred over lumens as a measurement of bulb output when we are trying to grow plants.

I realize that plants use accessory pigments such as chlorophyll _b_ and carotenoids to absorb other wavelengths in the PAR spectral range, but only chlorophyll _a_ can actively participate directly in light reactions. The accessory pigments have to transfer the energy to Chlorophyll _a_ which then initiates the light reactions, and that comes at a cost. So in that sense there is an optimum value.

However, in full spectrum bulbs, at least, I’m not totally convinced that PAR values differ significantly enough from lumens, in proportional terms, to worry too much about which measurement is more appropriate. This is especially so when you take in to account the photosynthetic contribution of accessory pigments. And when you also take in to consideration that most PAR meters available to the hobbyist aren’t really that accurate anyway…but just spit balling.

Anyway, back to the OP. Even if the PAR output of T8s only degrade 10% over 3 years it could be significant if the output drops below the threshold needed for the rate of plant growth you're happiest with; or worse the output drops below the photosynthetic compensation point of your plants. Clive is right in that both can be compensated for by increasing CO2 output; but only to a degree beyond which photosynthesis declines and therefore plant growth slows, and in the case of the latter the plant will eventually die. And this is conceivably more likely with T8s than with T5s (especially HO T5s) since the comparative output of T8s is much less to begin with.


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## Ravenswing (30 Jan 2013)

At the end of this Fluorescent Lights and Controls Myths - Facilities Management Lighting Feature it tells something about_ life hour service_. Thats something to think about but as Clive states above, plants do adapt usually well when changes are not too fast.


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## ceg4048 (30 Jan 2013)

Troi said:


> However, in full spectrum bulbs, at least, I’m not totally convinced that PAR values differ significantly enough from lumens, in proportional terms, to worry too much about which measurement is more appropriate. This is especially so when you take in to account the photosynthetic contribution of accessory pigments. And when you also take in to consideration that most PAR meters available to the hobbyist aren’t really that accurate anyway…but just spit balling.


The Apogee PAR meter is actually fairly accurate. There have been tests which compares it's performance to professional grade equipment and it has been shown to hold it's own.

Although auxiliary pigments do not directly interact in the Electron Transport Chain their energy transfer is just as important as the energy processing of the chlorophyll pigment itself. The Chlorophyll valence electrons must change their energy value from the "ground" state to a high enough energy value to escape the chlorophyll and to be captured by the Pheophytin, which is the primary electron acceptor, in order for it to be moved along the chain. The only cost associated with aux pigments are their assembly and fabrication. They are actually very efficient at energy transference as long as the distance between the two pigments is small, as long as the emission spectrum of the aux pigment and the absorption spectrum of the chlorophyll are similar, and as long as certain geometric parameters are satisfied. This energy transfer mechanism is a non-radiative method known as *F*luorescence *R*esonance *E*nergy *T*ransfer (FRET). It is FRET that allows the plant to be able to use all wavelengths in the visible spectrum, not just Blue and Red.

Even more important is the function of Auxiliary Pigments to fluoresce away photons when the energy inputs are too high, which damages the plant and actually inhibits growth rates. Also, another technique the plant can perform is to make better use of the inbound photons by increasing the pigment density, thereby increasing the probability of photon collision. It has been demonstrated that leaves under lower light intensity have a higher chlorophyll content and area density than leaves exposed to higher intensities. Therefore, small decreases in PAR doesn't really affect the growth rates that much assuming CO2 levels and nutrient levels are unlimited. That's where we get into trouble, because we lack the control to precisely measure any given parameter versus some other parameter.

PAR is a direct measurement of photon flux, i.e. it is a direct measurement of the number of photons crossing a unit area per second. Lumens is a "weighted average" and is a measure of the relative density of green and yellow photons in relation to the density of photons of other wavelengths. There is really no conversion between the two. They are measuring different aspects of the same phenomenon. That's why a large spectral shift can change the lumen value with only minor effect on the PAR. Of course, for any light source one can measure both values and compare, but this will only ever be an empirical comparison, not the derivation of a meaningful coefficient or conversion between the two. I think someone has actually done that and made a chart of the production numbers for different brands and wattages of bulbs. I can't locate it right now but it's quite useful because vendors always quote lumens, for good reason. It's done for brand new bulbs though, not old ones.

Cheers,


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## dw1305 (31 Jan 2013)

Hi all,


ceg4048 said:


> It has been demonstrated that leaves under lower light intensity have a high chlorophyll content and area density than leaves exposed to higher intensities.


You can actually see this, if you look at an _Anubias_ (or Ivy (_Hedera helix_), moss etc.) growing in heavy shade it is a really dark green, and that is what you are seeing in the "extra green", the extra chlorophyll.

You also get a change in the ratio of chlorophylls a & b. Photosystem II contain the majority of chlorophyll b and  "shade adapted chloroplasts", have an increased ratio of Photosystem II to Photosystem I, and a lower ratio of chlorophyll a to chlorophyll b. Increasing chlorophyll b increases the range of wavelengths absorbed by the shade chloroplasts. We do this as a class experiment with "shade" and "sun" Stinging Nettles (_Urtica dioica_), and it works really well.





cheers Darrel


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## niru (1 Feb 2013)

Looking at the graphs above, the lights dont seem to degrade much. I have T5 running 4+ years now without any noticable decrease in my plant growth. I know this because I count time needed for a stem to grow. Its rough estimate, but works. I have full EI, CO2 dosing, and about 9 hrs lights ON time.

Moreover, it takes a "relatively" long time for tubes to degrade (if you think they do). So plants have enough time to adjust to this PAR decrease. I agree with Ceg that theres no need to change tubes every 6 months / 1 year.


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## Tim Harrison (1 Feb 2013)

ceg4048 said:


> The Apogee PAR meter is actually fairly accurate. There have been tests which compares it's performance to professional grade equipment and it has been shown to hold it's own.
> 
> 
> Cheers,


 
Are you sure about that Clive...or...has the Matrix finally got you? Who's to say that the professional grade equipment is any good in the first place?



dw1305 said:


> Hi all,
> 
> You can actually see this, if you look at an _Anubias_ (or Ivy (_Hedera helix_), moss etc.) growing in heavy shade it is a really dark green, and that is what you are seeing in the "extra green", the extra chlorophyll.
> 
> ...


 
It's also often markedly noticeable in some plants with variegated leaves. When they are placed in shade the variegation disappears to a greater of lesser extent and new leaves emerge without, or with very little variegation.

But isn't the cost of shade adaptation offset by slower and/or less biomass accumulation? In nature a trade off is a strategy often necessary for survival. In our aquariums it doesn't have to be that way. I get the point that perhaps many of us are using more light than we need to (and maybe we don't necessarily need to worry too much about a little bulb degradation), but it does seem somewhat contradictory when most of us also go to great lengths to reduce the limits to growth to a minimum elsewhere, i.e. EI, flow, CO2, etc. And this especially so if your lighting is hovering on the edge of the photosynthetic threshold required to keep your plants healthy and growing.


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## dw1305 (1 Feb 2013)

Hi all


Troi said:


> But isn't the cost of shade adaptation offset by slower and/or less biomass accumulation?


It certainly is, there are other costs as well, the plant has to produce toxic secondary metabolites to protect all that valuable protein, and I would expect any really dark green shade plant to be stuffed full of alkaloids, calcium oxalate etc.


Troi said:


> I get the point that perhaps many of us are using more light than we need to (and maybe we don't necessarily need to worry too much about a little bulb degradation), but it does seem somewhat contradictory when most of us also go to great lengths to reduce the limits to growth to a minimum elsewhere.


I must admit that personally I don't worry too much about the light levels, and often have the plants under HPS grow-lights (400W Son-T) in the glasshouse, where they are getting huge amounts of natural light as well. My plants would always nutrient limited, but I can imagine that this wouldn't go very well with higher nutrient levels.


Troi said:


> i.e. EI, flow, CO2, etc. And this especially so if your lighting is hovering on the edge of the photosynthetic threshold required to keep your plants healthy and growing


I'm a CO2 agnostic and don't have any practical experience of added CO2, but Clive says that adding CO2 reduces the LCP, and I'm pretty sure he is right. In any system one resource will be limiting, the idea behind EI was that the limiting nutrient is always PAR, and that nutrients (including carbon) are always available. Light drives photosynthesis and more light means more CO2 and nutrients. There is more in this post and links <220 litres of failed ambitions - open to constructive criticism | Page 2 | UK Aquatic Plant Society>.

Again purely personally I'm not after maximal growth, in fact I'm after the lower possible rates of sustainable growth. You can think of this as the orchid, bromeliad, fern, succulent or alpine growing approach, it is aimed at growing plants with low potential growth rates in nutrient poor conditions.

cheers Darrel


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## ceg4048 (1 Feb 2013)

Troi said:


> Are you sure about that Clive...or...has the Matrix finally got you? Who's to say that the professional grade equipment is any good in the first place?


Yeah mate, I'm pretty sure. It's really not that difficult to make an accurate PAR meter. Light and electricity are part of the same phenomenon. In fact, the photon is the mediator of the electromagnetic force and that's why Einstein was able to very accurately describe the photoelectric effect 90 years ago.In fact it was the discovery of the photoelectric effect that triggered the development of quantum theory.

Electron energy gain from it's ground state is in direct proportion to the energy of the photon, and the energy of the photon is directly related to it's wavelength. So low energy photons such as Red are not able to pump the electron up sufficiently to escape the pull of the nucleus, but higher energy photons can displace the electrons entirely from their orbit, and the highest energy photons cause a higher electron exit velocity.

So, the energy gained by the electron is proportional to the frequency of the inbound photon. The coefficient of proportionality became known as Planck's Constant (h) which is used in almost every Quantum Theory equation and is super precise. So yeah, to a large extent, PAR meters are accurate, and they would have been accurate even if they were built back in 1920, because the smartest guys on the planet, at the time figured out the fundamental interaction of light and electricity. Remember that we're not talking about Nitrate test kits....





Of course, like all instruments, they need to be calibrated, and the difficulty with PAR meters has only to do with the response characteristics at different wavelengths, so there is some difference between their response and the plants pigment response.

We talked a little bit about it in PAR meter | UK Aquatic Plant Society

Cheers,


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## Tim Harrison (1 Feb 2013)

ceg4048 said:


> Yeah mate, I'm pretty sure. It's really not that difficult to make an accurate PAR meter. Light and electricity are part of the same phenomenon. In fact, the photon is the mediator of the electromagnetic force and that's why Einstein was able to very accurately describe the photoelectric effect 90 years ago.In fact it was the discovery of the photoelectric effect that triggered the development of quantum theory.
> 
> Electron energy gain from it's ground state is in direct proportion to the energy of the photon, and the energy of the photon is directly related to it's wavelength. So low energy photons such as Red are not able to pump the electron up sufficiently to escape the pull of the nucleus, but higher energy photons can displace the electrons entirely from their orbit, and the highest energy photons cause a higher electron exit velocity.
> 
> ...


 
 Ok...who are you really? ...Agent Smith! You can't scare me with this Gestapo crap. I know my rights. I want my phone call...


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## ceg4048 (1 Feb 2013)

I'm a sentient life form capable of moving in and out of any software path still hard wired to The System.
Inside The Matrix.....I am everyone......and I am no one.....

Cheers,


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## Ian Holdich (1 Feb 2013)

Clive is the Internet.


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## Ady34 (2 Feb 2013)

Ian Holdich said:


> Clive is the Internet.


We shouldn't believe him then.....


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## Tim Harrison (2 Feb 2013)

It's a pleasure chewin' the fat with you guys, this has to be one of the most challenging forums around, planted tank discussion or not.


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## Iain Sutherland (2 Feb 2013)

Ady34 said:


> We shouldn't believe him then.....


no problem there, cant believe him unless i understand him 

Its quite amazing the levels of knowledge and differing options on this forum from you guys, these threads are a great read even if most of it washes over.


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