Do t8 lights really degrade over time?

[ceg4048]

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,

 

[ian_m]

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.

 

[dw1305]

Hi all,

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.

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

 

[ceg4048]

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,

 

[BigTom]

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

 

[dw1305]

Hi all,

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

 

[ian_m]

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.

 

[dw1305]

Hi all,

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

 

[Tim Harrison]

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,

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.

 

[Ravenswing]

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.

 

[ceg4048]

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 Fluorescence Resonance Energy Transfer (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,

 

[dw1305]

Hi all,

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

 

[niru]

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.

 

[Tim Harrison]

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?

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.


cheers Darrel

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.

 

[dw1305]

Hi all

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.

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.

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

 

[ceg4048]

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,

 

[Tim Harrison]

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,

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...

 

[ceg4048]

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,

 

[Ian Holdich]

Clive is the Internet.

 

[Ady34]

Clive is the Internet.

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