LED Lights: The future's here!

[ishaan]

Good info Sir ,what i have concluded that lighting for a tank is very very difficult to calculate because of various factors

[syed.ali]

Thanks for sharing the information, but most of the time all these rating are just not available. Few of them will be able to tell Kelvin.

So will it be best to say that we buy LED with kelvin rating more than 6500k and possibly try using a Combination of Pure White with Blue color LED ? Please share your thoughts

[fishy.man]

Hi,
LED, there is only one good thing about LED, it does not lose its efficiency with age but phosphorus tubes do.
but do you have spectral distribution of LED is not available, if yes please post it here and i will be able to tell you which one to go for.
this way may be i can find something good too for my aquariums.
I am also tired of paying heavy electricity bills.
I saw a friend of mine Bappa using LED but it wasnt his main tank but dump tank.
Let me look for LED spectrums around and may be I can provide information.

regards

fishyman

[syed.ali]

This are 2 threads on the http://www.plantedtank.net, which i have used for my lil understanding

http://www.plantedtank.net/forums/light ... lbs-2.html

This one is amazing read, the guy has excellent work on the effect of light in respect to watt, kelvin, hood and distance. Its about general lighting concept but excellent data

This one is for LED
http://www.plantedtank.net/forums/light ... ndium.html

i hope they help

Another 1 i missed was this, it explains some basic
http://reefledlights.com/ledmytank/

[fishy.man]

Hi,
I mentioned in my last post that any planted aquaria would need more of blue spectrum than red for obvious reasons.
check this image....

If you noticed chlorophyll A,B and carotenoids require max of blue spectrum that means higher kelvin temperatures and then almost drops down to bare minimum starting from 530 nm that is where your lumen values starts to peak for human eye(brightness) but plants dont want them and then it again is peaking up around 640 nm till 730....

regards
Fishyman

[marsaiko]

Thanks Tarun,

Issue here is what LED is being sold in market? do you know the name please?

[fishy.man]

hi there,
I am talking about general spectrum that plants need...what I am telling you is please get the spectrum chart of any LED compare it with this one and then buy....
or you can post here for all of us to see...

fishyman

[fishy.man]

Light Intensity in an aquarium:-

Good at last we have a possibility of analyzing the real data based on simple experiment to prove the movement and intensity changes of light in Water which actually would contribute to Photosynthesis...lot of this was discussed in the "A Comparison Between Light Sources Used in Planted Aquaria " By Ivo Busko, long time ago but some serious discussion never happened, the copy of the article can be read at :-

Aqua Botanic-light bulb comparison

Also having read some chapters of "Light and Photosynthesis in Aquatic Ecosystems" second edition by John T.O. Kirk some of the following parameters do apply to light physical properties as it travels from the source to water and into it, primarily which are as:-

· A photon of wavelength 700nm from the red end of the spectrum will have less energy from a photon at 400nm from the blue end of the spectrum. where energy = (1988/ λ) X 10-19 Joules,where λ = wavelength

· Hence at 400nm the energy of a photon is 233.33% more than the energy of a photon at 700nm.(energy at 400nm = (1988/400) x 10-19 Joules = 4.97 x10-19 J and at 700nm it is 2.84 x10-19 J)

· Light travels at a velocity equal to the velocity of light in a vacuum divided by the index of refraction (n), which is typically for water n = 1.33. Water 100'C 1.31; Water 20'C =1.33335 & Water 35'C = 1.33157

· Hence the velocity in water is about 2.25x10^8 m/s. Because light travels slower in water than in air, some light is reflected at the water surface. For light shining straight down on the water, the reflectivity is (n - 1)2 / (n + 1)2.

· For freshwater, the reflectivity is 0.02 = 2% at zenith angle of incidence between 0 to 20 degrees and then it remains low increasing rapidly after 50 degrees, to 89.6% reflectance at 89 degrees of incidence angle.


See Chart below:-


Zenith Angle Of Incidence Degrees Reflectance %


0 deg 2.0% 50 deg 3.3%
5 deg 2.0% 55 deg 4.3%
10 deg 2.0% 60 deg 5.9%
15 deg 2.0% 65 deg 8.6%
20 deg 2.0% 70 deg 13.3%
25 deg 2.1% 75 deg 21.1%
30 deg 2.1% 80 deg 34.7%
35 deg 2.2% 85 deg 58.3%
40 deg 2.4% 87.5 deg 76.1%
45 deg 2.8% 89 deg 89.6%

Reflectance of Unpolarized Light from a flat Water Surface assuming that the water has a refractive index of 1.33See – Fresnel’s Equation
Hence most sunlight reaching the water surface is transmitted into the water, little is reflected. This means that light incident on the water surface in the aquarium is mostly absorbed below the water surface.

At this moment on water surface and just below the water surface light or photons are lost by absorption and scattering out of path and Gain by scattering into path. Also there is a factor of refraction and reflection of light at air –water boundary as shown below :-







Refraction and reflection of light at air-water boundary. (A) A light beam incident from above is refracted downwards within the water: a small part of the beam is reflected upwards at the surface. (B) A light beam incident from below at a nadir angle of 40° is refracted away from the vertical as it passes through into the air: a small part of the beam is reflected downwards again at the water-air boundary. (C) A light beam incident from below at a nadir angle greater than 49° undergoes complete internal reflection at the water-air boundary.
Ref:- (Source Page 45 Light and Photosynthesis in Aquatic Ecosystems)

Also how much light is reflected or refracted depends on the wind speed and disturbance of the water surface by wind , in case of a aquarium it can be attributed to water movement on the surface due to Air Pumps, CO2 diffuser or power heads.

The light absorbing components of the aquatic system are :-

· The Water Itself
· Dissolved Yellow Pigments
· The Photosynthetic biota
· Inanimate Particle matter

Water:-
Water though it appears colorless in small quantities is blue in colour and it absorbs light more in the region from 550nm and above quiet significantly in the red region. It has been found out that about 35% of incident light at 680nm is absorbed at 1 meter depth of water or 1 meter thickness of water. So if we were to refer the absorption Coefficients derived from the published attenuation coefficient Morel & Prieur 1977 you would see that at 380nm the value is as 0.023 , 400nm = 0.018 ; 450nm = 0.015; 500nm = 0.026; 550nm = 0.064 ; 600nm = 0.157; 630nm = 0.310; 650nm = 0.350 ; 670nm = 0.430; 680nm = 0.450; 690nm = 0.500 and at 700nm it is 0.650;
At 740nm ,760nm and at 800nm the values are as 2.38, 2.55 & 2.07


Hence Blue light is absorbed least, red light is absorbed most strongly.

Attenuation per unit distance is proportional to the radiance or the irradiance of light where x is the distance along beam, c is an attenuation coefficient and I is irradiance.

dI/dx = -cI



Figure Absorption coefficient for pure water as a function of wavelength λ of the radiation. Redrawn from Morel (1974)

If the absorption coefficient is constant, the light intensity decreases exponentially with distance.

I2 = I1 exp(-cx)

where I1 is the original radiance or irradiance of light, and I2 is the radiance or irradiance of light after absorption.

Actually the contribution of water itself to the attenuation of PAR by absorption of quanta is important only above about 500nm, and where we use artificial light which have more spectrum in blue and blue green range rather than at red, yellow - red range ( a good full spectrum light may have a good ratio of red : blue though the light may be towards or around 3500K to 4000K) would mean that more red light or photons are lost compared to the blue as they travel downwards with in water, now how much of this loss is significant to an aquarium where the water depth may not be more than 18 to 24 inches ( 1 meter = 39.37 inches) is a question one has to measure and check ; hypothetically more blue light reaches the plants than red as we go downwards the depth of water from surface.

Humic, Tanin etc:-
From the point of view of photosynthesis water soluble humic substance impart yellow colour in water and this leads to absorption of light particularly at the blue end of the spectrum. Yellow material of the humic type can also be generated by decomposition of plant mater with in the water body.

So due to tanin, humic acid in water Blue light is absorbed more towards the 400nm to 550nm region and much less at and beyond (drops significantly) at 600nm region.

Particles:-
The inanimate particulate matter in water and their typical concentration does not absorb light strongly but scatters quiet intensely but studies have shown that absorption is low or absent at the red end of the spectrum and rises steadily as wavelength decreases into the blue end of the spectrum.

The Photosynthetic biota:-
The Absorption of Light by the photosynthetic pigments – chlorophylls, carotenoids , biliproteins etc contributes to the attenuation of PAR with depth. Specific absorption coefficient corresponding to 1mg of chorophyll a per unit area of 1 meter cube is as :-

At 400nm = 0.017, 450nm = 0.024 ; 500nm = 0.018 ; 550nm = 0.011; 600nm =0.007 650nm= 0.014 & at 700nm= 0.003 so it is a maximum around 440nm almost touching 0.025 and then dipping at around 575nm and again peaking around 670nm at 0.018 almost like the photosynthesis action spectrum curve.

Hence as light travels through the depth of water there is significant amount of light loss due to various factors like water depth itself, tanain humic acis, other particles , dust, and then the chlorophyll from algae & plants itself, hence a combination of these contribute to light loss in water or loss of photons in water.

Scattering of Light within the aquatic medium also contributes towards the availability of photons for photosynthesis. Many of the photons undergo scattering one or more times before they are absorbed . Scattering does not remove the photon but the photons have to travel more in a zig zag path as they get scattered and this increases the total path length traveled by them which may result in capture of the phonon by one of the components of the absorbent medium (water) as mentioned above. In addition some photons are scattered back in upward direction thus the effect of scattering is directly related to the light or photon intensity and the vertical attunation of light in water due to scattering of light by density fluctuation or by particle scattering.

Scattering of pure water is of the density fluctuation type and varies with wave length. Experimentally scattering is found to vary in accordance with 1/λ4.32 . The scattering coefficient of natural waters are invariably much higher than those of pure water. See table below:-

wavelength scattering coefficient/ meter


Pure Water

400nm= 0.058
450nm= 0.0035
500nm= 0.0022
550nm= 0.0015
600nm= 0.0011


Pure Sea Water

450nm= 0.0045
500nm= 0.0019

Marine Water
Atlantic Ocean Sargasso Sea
440nm= 0.04
633nm= 0.023

Pacafic Ocean Galapagos Is.
440nm= 0.08
655nm= 0.07

Fresh Water- River
Irondequoit Bay Ontario
400-700nm= 1.9-5.0
Perry - Tasmania
400-700nm= 0.27
Gulungul - Myrray Darling System
400-700nm= 5.7


Fresh Water- LakesRotokakahi
400-700nm = 1.5Rotorua
400-700nm = 2.1D
400-700nm = 3.1

Hence
Attenuation of light in the water column – due to absorption and scattering

Transmittance (amount of light left) = Iz/ I0 x 100
where I = irradiance,
I0 = irradiance just below surface
Iz = irrad. at depth z

Absorbency [100 x (I0 - Iz)]/I0



Figure Left: Attenuation of daylight in the ocean in % per meter as a function of wavelength.
I: extremely pure ocean water; II: turbid tropical-subtropical water; III: mid-latitude water; 1-9: coastal waters of increasing turbidity. Incidence angle is 90° for the first three cases, 45° for the other cases. Right: Percentage of 465nm light reaching indicated depths for the same types of water. From Jerlov (1976).

Attenuation equation
Iz = I0 e - kz
where e = natural logarithm
k = attenuation coefficient (extinction coefficient ref- Wetzel)
characteristic for each water body and each wavelength
often converted to a linear plot by taking the log of both sides:
ln Iz = ln I0 – kz


Components of the attenuation/extinction coefficient

K_l = K_abs + K_ scattering
K = K_water + K_dissolved organics + K_particulates


K_water
- for pure water, absorption at long wavelengths dominates (>550 nm; red and IR)
- So, IR disappears in the top 1-2 m of most lakes
- Scattering at short wavelengths, <380 nm
- Pure water does not absorb UV (only scatters it)
- Dissolved salts do not increase attenuation


K_dissolved organics
- dissolved organics - humic and fulvic acids
- absorb strongly at short wavelengths -- blues and UV's (<500 nm)

K_particulates
- absorbs light evenly over the entire spectrum
- often the particulates are predominantly tripton and phytoplankton
-detritus may have higher absorbance at the blue end


Hence based on these transformation that Photons or light undergo while they travel from source to the plant leaves we should conduct experiments to measure the following:-

1. Measurement of PAR right at the Source
2. PAR Values as they change over with use of correct reflector
3. PAR at Tank bottom with out any water, only AIR
4. PAR at water surface & just below with out any water movement
5. PAR at water surface & just below with water movement – diffusers, power heads , filters etc.
6. PAR at various levels or depth in water may be with a 1 inch gap.
7. PAR at various plant canopy level ( Tall / Medium/ Low height Plants)
8. PAR at Substrate
9. PAR at different Water types – Clear Water; Black water etc

This will help is collate the data collected based on studies as described above and then actual measurements results which this experiment will lead to better use (efficiency & economical) of artificial light for aquaria.

Though this article explains the physical property of light as it travels from an artificial source like a fluorescent or a MH light light in an aquarium through Air into Water and ultimately reaches the plant leaves ( also same principle is applicable to natural light), Actual photosynthesis which a plant may undergo depends on many more factors but this information will at least help to understand how much PAR a particular bulb or alight source may contribute at water surface and at the substrate and over plant canopies and how & Why the PAR values change as they travel with in water. Thus we might be able to predict to some extent the right amount of light an aquarium may need based on these principals. This also in general states that Watts per gallon rule may not significantly contribute to a scale of measurement or a baseline as light under goes significant changes as it travels through water and plants adopt differently to the available light over a period of time provided that the other parameters of CO2 and Fertilization are kept at optimum level for plant growth. Significantly it has been found that Light is not the limiting factor for plant growth (just as our eyes can adjust to bright and dull light) as much as to CO2 or the available nutrients in water.

An interesting reading may be this article on effect of light on growth and photosynthesis of Egeria najas at :-
http://www.scielo.br/pdf/babt/v46n2/16288.pdf

Hope this helps.

This work is done by a dear friend of mine i just posted here on his behalf....

[marsaiko]

you got some awesome friends there!!!
Why dont you invite them on to the forum as well.