Lighting in Planted Tank

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Lighting in Planted Tank

Postby Rohan » Sat Apr 07, 2012 5:02 pm

Wanted to initiate a discussion on the lighting in Planted setups.

Everyone has heard of Watt per gallon rule when they started planted journey.

But i am sure many of you have read that this rule is vague enough.

Another process of determining the light is "Lux per square inch"

How many of you agree that the latter is more efficient than than former or is there any other better way to determine the amount of light needed to grow plants?

Also which method does you individuals follow?

Please share your experiences :)
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Re: Lighting in Planted Tank

Postby Rohan » Mon Apr 09, 2012 10:36 am

Guys please share something :P
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Re: Lighting in Planted Tank

Postby abhirup » Fri Apr 13, 2012 8:52 pm

Its a huge topic rohan...You have to consider hell lot of factors..These are just some commonly used guidelines which are generally used for simplification...But if you need to understand the best light for your plants you have to consider many things...
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Re: Lighting in Planted Tank

Postby Tirtha » Fri Apr 13, 2012 9:18 pm

Somehow I missed the topic earlier. Will get back to it soon tomorrow.
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Re: Lighting in Planted Tank

Postby abhirup » Sat Apr 14, 2012 7:20 pm

With inputs from Sujoy da I once had prepared a document on this. We had a very good discussion on this topic in orkut community once..
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Re: Lighting in Planted Tank

Postby Rohan » Sat Apr 14, 2012 7:29 pm

@ Tirtha da and Abhirup da

Could you please all initiate this topic here :)

Abhirup da,is the document ready or still under processing ? :D
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Re: Lighting in Planted Tank

Postby prajjwal » Sat Apr 14, 2012 7:30 pm

That orkut discussion was soo informative that I saved those in separate file :)

Who knows that some day orkut may vanishes from net!! :lol:
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Re: Lighting in Planted Tank

Postby Rohan » Sat Apr 14, 2012 7:33 pm

Prajjwal da please share the infos here then :D
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Re: Lighting in Planted Tank

Postby abhirup » Sat Apr 14, 2012 7:43 pm

yes I have the document...I just need to search it in my system..
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Re: Lighting in Planted Tank

Postby abhirup » Sat Apr 14, 2012 8:30 pm

Lighting in a Planted Aquarium

For proper growth of plants in an aquarium lighting is one of the most essential factors
.Plants prepare their food by the process photosynthesis only in the presence of proper
light. Without sufficient light photosynthesis will be impaired and plant health will be
diminished. Providing a suitable light source along with other environmental conditions
will ensure plants to perform photosynthesis at an optimum rate. To ensure this proper
lighting must be provided to the aquatic plants and to do this it is important to understand
how plants utilize light.

To start with we must understand what is Photosynthesis ?
Photosynthesis is a process that converts carbon dioxide into organic compounds,
especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae,
and many species of bacteria. With the exception of some bacteria, all use water and
carbon dioxide as initial substrates and release oxygen as a waste product.
So Plants needs energy for their daily activity and this energy is supplied by
Photosynthesis which uses light as a component of the process.

Although photosynthesis can occur in different ways in different species, some features
are always the same. The Photosynthesis process always begins when energy from light
is absorbed by proteins that contain chlorophyll.

In plants, these proteins are held inside organelles called chloroplasts, while in bacteria
they are embedded in the plasma membrane. Some of the light energy gathered by
chlorophyll is stored in the form of adenosine tri phosphate (ATP).

The rest of the energy is used to remove electrons from a substance such as water. These
electrons are then used in the reactions that turn carbon dioxide into organic compounds.
In plants, algae and cyano-bacteria this sequence of reactions is called the Calvin cycle,
but different sets of reactions can be found in bacteria, such as the reverse Krebs cycle in
Chlorobium.

Many photosynthetic organisms have adaptations that concentrate or store carbon
dioxide.
The general equation for photosynthesis is therefore:
CO2 + 2 H2A + photons → (CH2O)n + H2O + 2A
carbon dioxide + electron donor + light energy → carbohydrate + oxygen + oxidized
electron donor
Since water is most often used as the electron donor in oxygenic photosynthesis, the
equation for this process is:
CO2 + 2 H2O + photons → (CH2O)n + H2O + O2
carbon dioxide + water + light energy → carbohydrate + oxygen + water
So as one can understand that Photon (In physics, a photon is an elementary particle, the
quantum of the electromagnetic field and the basic unit of light and all other forms of
electromagnetic radiation.) is required for photosynthesis, in simple terms light is
required for Photosynthesis...

Plants absorb light primarily through chlorophyll, which is the reason that most plants
have a green color.

Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls.
Similarly algae also use chlorophyll, but various other pigments are present as
phycocyanin, carotenes, and xanthophylls in green algae,
phycoerythrin in red algae (rhodophytes) and fucoxanthol in brown algae and diatoms
resulting in a wide variety of colors.

A small note on Carotene : Carotene is an orange photosynthetic pigment important for
photosynthesis. Colour in Carrot for example of Carotene.
Carotenes contributes to photosynthesis by transmitting the light energy they absorb from
chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet
oxygen, an excited form of the oxygen molecule O2 which is formed during
photosynthesis.

It comes in two primary forms designated by characters from the Greek alphabet: alphacarotene
(α-carotene) and beta-carotene (β-carotene).
Gamma, delta, epsilon, and zeta (γ, δ, ε, and ζ)

A small note on Xanthophylls...
Xanthophylls (originally phylloxanthins) are yellow pigments from the carotenoid group.
They are found in the leaves of most plants and are synthesized within the plastids.
They are involved in photosynthesis along with green chlorophyll, which typically covers
up the yellow except in autumn, when the chlorophyll is denatured by the cold.
In plants, xanthophylls are considered accessory pigments, along with anthocyanins,
carotenes, and sometimes phycobili proteins. Xanthophylls, along with carotenic
pigments are seen when leaves turn orange in the autumn season
So far we have understood that Light as photons is required by plants for photosynthesis
and mostly these light harvesting pigments are present in the leaves of the plants as most
of the energy is captured in the leaves.

The cells in the interior tissues of a leaf, called the mesophyll, can contain between
450,000 and 800,000 chloroplasts for every square millimeter of leaf.
The surface of the leaf is uniformly coated with a water-resistant waxy cuticle that
protects the leaf from excessive evaporation of water and decreases the absorption of
ultraviolet or blue light to reduce heating.

The transparent epidermis layer allows light to pass through to the palisade mesophyll
cells where most of the photosynthesis takes place.
Now an other thing is that this process is divided into two parts ..

One part is Light Dependent Reaction :-
In this light reactions, one molecule of the pigment chlorophyll absorbs one photon and
loses one electron. This electron is passed to a modified form of chlorophyll called
pheophytin, which passes the electron to a quinone molecule, allowing the start of a flow
of electrons down an electron transport chain that leads to the ultimate reduction of
NADP to NADPH.
So basically the Light Dependent Reaction is what needs the Photon of Light ...

Now for the Light Independent Reaction ...
In the Light-independent or dark reactions the enzyme RuBisCO captures CO2 from the
atmosphere and in a process that requires the newly formed NADPH, called the Calvin-
Benson Cycle, releases three-carbon sugars, which are later combined to form sucrose
and starch.

The Calvin cycle and carbon fixation to be more specific, carbon fixation produces an
intermediate product, which is then converted to the final carbohydrate products. The
carbon skeletons produced by photosynthesis are then variously used to make other
organic compounds...

Not all wavelengths of light can support photosynthesis. Plants are able to use visible
light only from wavelengths of about 400 to 700 nm and this range is termed
Photosynthetically Active Radiation (PAR). Primarily, red and blue light are used in
photosynthesis while green light is reflected or transmitted and thus, plants appear green
because green light is not absorbed by plant pigments.

The photosynthetic action spectrum depends on the type of accessory pigments present.
For example, in green plants, the action spectrum resembles the absorption spectrum for
chlorophylls and carotenoids with peaks for violet-blue and red light.
In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for
blue-green light, which allows these algae to grow in deeper waters that filter out the
longer wavelengths used by green plants. .

An action spectrum is the rate of a physiological activity plotted against wavelength of
light. It shows which wavelength of light is most effectively used in a specific chemical
reaction. For example, chlorophyll is much more efficient at using the red and blue
spectrums of light to carry out photosynthesis. Therefore, the action spectrum graph
would show spikes above the wavelengths representing the colors red and blue.
chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while
chlorophyll b has approximate maxima of 453 nm and 642 nm, carotine at approximately
442nm , 472nm.

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Phycoerythrin is a red protein from the light-harvesting phycobiliprotein family, present
in cyanobacteria, red algae and cryptomonads. A strong emission peak exists at 525 & at
575 ± 10 nm, So you see Phycoerythrin absorbs slightly blue-green/yellowish light
mostly used by Red algae ?

Phycocyanin is a pigment from the light-harvesting phycobiliprotein family, along with
allophycocyanin and phycoerythrin. It is an accessory pigment to chlorophyll.
Phycocyanin absorbs orange and red light, particularly near 605-620 nm..
One other important thing for Aquatic Plants is that they have Epidermal Cells that have
well developed Choloroplasts and that Stomata is absent or scare in submerged leaves
and CO2 is directly taken up through the epidermal cell wall. This is a very important
difference for Submerged Aquatic Plants and Terrestrial Plant Leaves.

So Basically Photosynthesis uses light as Photons for the Process.
Though Light from wavelength 400 nm till 700 nm is said to be used but mostly as you
will see in this graph :-
that
1. Cholorophyll a Uses light between 350 nm- 450 nm and again from 650-680nm approx
and has a very weak absorption between 450nm and 650nm, peaks at the blue 430nm and
in the red at about between 661nm -667nm (peaks at 662,670,677 nm)
2. Cholorophyll b Uses light between 395nm- 490nm and again from 620-670nm approx
and has a very weak absorption between 490nm and 620nm peaks at the blue 453nm and
in the red at about between 642nm.
3. Carotenoids uses light between 350nm and 520nm and peaks twice at 442-450 and 472
nm approximately. They absorb short wavelength of visible light and which is why their
colour is mostly yellow, orange or red.
4. Higher Plants and some green algae use or rely mostly on Cholorophyll a +
Cholorophyll b for light harvesting and the general ratio of Cholorophyll Pigments and
Carotenoids is 3:1
5. Now the energy absorbed by Chlorophyll b is transferd with 100% efficiency to
Chlorophyll a.
Energy absorbed by Carotenoids is transferd with less efficiency to Chlorophyll b and
then to chlorophyll a.
6. Energy absorbed by Phycocyanin uses light between 450 nm and 655 nm peaks at
605nm.

The energy from Phycocyanin is then transfered to allophycocyanin and then to
Chloroplyll a.
Thus no mater which pigment captures the light photons first the absorbed energy always
ends up in Chlorophyll a and then is moved into a reaction centre, where it is
immediately trapped and used for electron transfer.

So we are now mostly concerned with light spectrum between 350nm and 490nm and the
between 620 nm and 680 nm. Visible Light is between 380 nm till 750nm
(Photosynthesis Spectrum is between 400nm and 700nm)which is Violet Blue - Blue
Spectrum and then with red, near red and some far red part of the spectrum. But just
because plants mainly use the above spectrum for photosynthesis, if the others spectrums
are not used like if green light is not present, the plants will look grayish and pale with an
artificial effect. Thus a perfect balance of blue, green red lights must be supplied for
proper photosynthesis and visual satisfaction. The normally fluorescent tubes that are
available in the market are made for our use and is sensitive to our eyes and contains
wavelength close to 530nm which is most sensitive to human eyes. But the requirement
of the plants are different. Hence a fluorescent tube must be wisely selected keeping all
the factors in mind.

Light travels much faster in air than water. When lights enters water from air its velocity
changes and its intensity decreases. Longer wavelengths of light are easily absorbed in
the water column while the shorter wavelengths can penetrate more in water. Although
plants are more sensitive towards red light for photosynthesis, blue light must be used as
red light is not available to plants which are placed deeper in the aquarium and is only
available near the surface. But this does not mean that blue light must be present in large
quantity as strong blue light promotes algal growth hence a balance of red and blue light
must be used.

Light quantity

Light intensity is an expression of how much light (energy) reaches a given surface and
in natural sciences, light intensity is measured in μmol photons per square meter per
second (μmol m-2 s-1). In the aquarium hobby, Lux has traditionally been used to
measure light because quantum sensors are extremely expensive devices, whereas lux can
be measured by an old-fashioned light meter used in photography. As a rule of thumb, 1
μmol m-2 s-1 is equivalent to 55 Lux in the PAR spectrum but this conversion is not
accurate since the Lux scale has been developed to suit the eye’s sensitivity and thus, it is
not the same for all color combinations. In aquarium hobby another method of
determining light intensity is used called the Watt per Gallon Rule. This rule is pretty
misleading and wrong. Watt is the unit of electrical energy consumed. It has no relation
with light intensity. It does not give us any idea about how much light is reaching a
particular water surface. So while choosing lighting for an aquarium right intensity must
be of prime importance than wattage of the light.

In nature, many aquatic plants are found in places where they receive direct sunlight
(2000 μmol m-2 s-1) at least part of the day. Not even plants growing in shade receive
less than about 200 μmol m-2 s-1 at noon. In comparison, a very well illuminated
aquarium receives about 80-100 μmol m-2 s-1. This is a dramatic reduction in energy
supply, but it is nevertheless what most aquarium plants face when they are transferred
from the well-illuminated nursery, where most plants are grown emergent, to the low
light environment in the aquarium. As a consequence, many plants lose their terrestrial
leaves and new ones are formed. These new leaves are much better adapted to light
harvesting under low light in the aquarium, where it becomes important to capture every
single photon that reaches the leaf surface. Unfortunately, a large proportion of the light
that is emitted never reaches the plants. Light is emitted in all directions and only beams
that hit the water surface almost perpendicular penetrate the water surface, while the
remaining light is reflected. In order to make maximum light energy penetrate the water
surface a parabolic reflector must be used as after reflection from the reflector the angle
on incidence of most of the light energy on the water surface is almost perpendicular.
Once the light has successfully penetrated the surface, the depth of the tank is the most
important factor controlling how much light reaches the bottom. The light intensity
decreases dramatically with distance from the lamp. For example, if 50% of the light
reaches an area at a depth of 10”, then only 25% will reach that area at a depth of 20”.
Most of this reduction is due to the fact that the light beams are not totally parallel and
thus, much light is scattered on its way to the bottom. Another part is absorbed by colored
substances such as humic acids dissolved in the water and by particles suspended in the
water (mostly microscopic algae and detritus). In conclusion, much of the useful
wavelengths have been filtered before the light reaches the bottom of the aquarium.

Illumination Time

The optimum illumination time is approximately 12 hours for most plants. Any additional
light does not really benefit the higher plants, whereas algae are always able to capitalize
on the extra energy provided. On the other hand, a significantly short period of
illumination has an adverse effect on the plants. They simply do not get enough energy
and they start losing leaves, particularly the lower ones. It must also be noted that a plant
must get a complete dark period when it can perform its other biological functions.
However in an aquarium 9-10 hours of lighting in sufficient considering others factors
which are different from nature in an aquarium. Moreover we don’t want the plants to
grow that big even in an aquarium as in nature.

Choosing correct types of light


The best type of light to choose depends on the function it has to perform. For optimum
plant growth the light must give an output of high light intensity and must generate less
heat. The normal incandescent bulbs are inefficient and produces a lot of heat. The
fluorescent tubes are pretty effective as they convert more electrical energy into light
energy than heat energy. There are different types of fluorescent tubes like T12 T8
T5.The T8 lights have better penetration power than T12[which are not used now-a-days]
while the T5 has higher efficiency and penetration power than T8. A new type of
fluorescent tubes namely T5 HO[high output] are now-a-days used which can even
penetrate more than the T5 tubes and provide high intensities and are highly efficient.
While selecting light height of the tank is a very important factor as it determines how
much distance the light rays penetrate in water. As the general thumb rule says T8 lights
are effective till the height is 15 inch, for height more than 15 and 22inch T5 or T5 HO s
are most effective. If the height is more than 22inch the fluorescent tubes fail to deliver
the necessary intensity required. Hence for tanks with more height must use metal halides
which provide high output and intensity but must be hung at least 1feet above the
aquarium for ample ventilation and dissipation of heat.
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