Tbub1221;914308 wrote:
the coral don't see so it doesn't know wether or not its 10k or 20k , just that the nm it requires is present and at a usable par. The difference is rather than just 450nm which is royal blue it also has other nm ranges needed even though that's the strongest peak.
The different temps 6500k 10k etc are only names we use do describe a target spectrum because we can't see the nm or par with our eyes , but we know through technology that these colors Cary these better.
.
Introduction to PUR
http://www.advancedaquarist.com/2005/12/aafeature2">http://www.advancedaquarist.com/2005/12/aafeature2</a>
[QUOTE=]
The color temperature of a light bulb, or more precisely its extrapolated value, gives us more information about its dominating wavelength than about its real spectrum. The table below can give you a few educated clues. You will note that heated at 5,500 K, a black body emits about the same energy in all wavelengths, and that is light spectrum is usually called "daylight". Below this value, light tends to become yellow, above it becomes blue - even if our eyes do not necessarily sense this.
Here are some values:
Candle light: 600 K
75 W common light bulb: 2850 K
150 W common light bulb: 3,000 K
Halogen light bulb: 3,400 K
Daylight: 5,500/6,500 K
Cloudless sky: from 10,000 to 20,000 K
Not only is it important to know how to judge light's quality, in fact its spectrum, it is also important to judge:
the quantity of light generated by a source (in all directions),
the quantity of light reaching the target surface
Because things are never really simple when light is concerned, there are many units used that relate to the different light properties related here.
The Watt and Watt/m2 refer to the amount of energy consumed by the source and the amount of energy emitted by a given surface.
The lumen and the lux (1 lux = 1 lumen/m2) originated from industrial standards and are linked to a reference light source (540x1012 Hertz and 1/683 Watt). Our eyes are particularly sensitive to this wavelength (yellow-green). Lumen and lux are then better used for the qualification of commercial light sources targeting our visual comfort, and are less useful when studying biological phenomenons like photosynthesis (read below).
The micro-Einstein (µE) quantifies the amount of photons emitted or received by a body. One Einstein is equivalent to one mole of photons (6.023x1023 photons). This unit doesn't take into consideration the energy carried by the photons (this energy depends on the wavelength). Why should we be interested by this unit? There are two answers.
The first answer will help us to slightly deflate the ego of the person who proudly bought a 14,000 K metal halide bulb: "Yeah... Right... You know... What matters to corals is the PAR. Your bulb, how many micro-Einsteins does it have?" If your friend has a clue about the PAR, then start asking him about the PUR (more on that later).
Seriously, the right answer is that the Einstein is a good indicator of the photosynthetic activity of plants. The biological mechanisms in place during the luminous phase of photosynthesis do not depend on the photons' energy, but on their number. This is exactly what the Einstein displays. The PAR (Photosynthetic Available Radiation, unit µE/m2/s) measures the number of photons reaching a surface, all this in the wavelengths of the visible light (between 400 and 700nm). It is indeed in this portion of the spectrum that we can find the different absorption peaks of the photosynthetic pigments. As these pigments do not absorb energy in a equal manner on all that 400-700nm range, but only at certain precise wavelengths, some prefer using the PUR (Photosynthetic Usable Radiation) in order to quantify the number of photons truly used by the photosynthetic cells. The PUR is thus defined by the light source (emitted spectrum, intensity) and by the studied pigments (because of their absorption spectrum). This one is probably better left to specialists...[/QUOTE]
Edit: [QUOTE=][B]Sn4k33y3z;915027 wrote:[/B] It seemed a bit like a promotion for ecotech radions, backed with lighting terminology IMO.
Edit: It seemed a bit like a promotion for ecotech radions, backed with lighting terminology IMO.[/QUOTE]
The 2012 feature article, Light in the Reef Aquaria?
lol.
Edit: You really have to click the link and view the graphs, but here
[QUOTE=]Perhaps every reef hobbyist is willing to provide the "right" light to his corals - both correct spectrum and sufficient intensity are important. Before we consider how to implement this "right light," we shall first try to understand what kind of light marine organisms get in their natural environment.
As our starting point, consider the spectral distribution of solar energy in Fiji in July, Fig. 1:
Fig. 1 Spectral distribution of sunlight energy at the level of the sea
The horizontal axis of the graph is wavelength, in nanometers, and the vertical axis is spectral irradiance, in W/m2·nm. The human eye is sensitive to radiation in the range between approximately 400 and 700nm, therefore we marked the wavelength ranges shorter than 400nm (ultraviolet light) or longer than 700nm (infrared radiation) in black, whereas visible wavelengths are colored as they are perceived by the eye.
The chart in Fig. 1 has been obtained from the solar spectrum at the boundary of the earth atmosphere using the SMARTS 2.9.5 scientific simulation software. This simulator takes into account light absorption by various components of the atmosphere as well as scattered light from the sky.
Let us now try to find out what kind of light spectrum is available to marine organisms in their natural environment. In our attempt to build an ideal light fixture for our reef tanks we shall try to generate a similar spectral distribution at certain depths underwater.
Different coral species live on various depths: some live in very shallow waters, whereas deep water corals, such as Bathypates spp., can be found on the depths of up to 8000 meters (about 5 miles). About 20% of all coral species are non photosynthetic; they do not require any light as a food source. Most corals, however, are photosynthetic, and these are the species which are kept most often at home aquaria. We shall try to figure out what kind of light they prefer.
Consider the graph of solar light penetration into marine water, depending on wavelength, compiled by the Institute for Environment and Sustainability of the European Commission [4] (Fig. 2):
Fig. 2 Penetration of light into seawater, depending on wavelength
The horizontal axis is the light wavelength, in nanometers, and the vertical axis is depth, in meters, at which the intensity of that wavelength is equal to one percent of the intensity at the surface. It is clear from this graph that wavelengths between approximately 370 and 500nm best penetrate into the depth. In other words, violet and blue parts of the spectrum penetrate best into seawater, whereas green light is much worse at that, yellow-orange is even worse, and red light with wavelengths longer than 600nm is only capable of penetrating very shallow waters.
The light spectrum on the surface can be defined as a function I0(λ), where λ is the wavelength and I0 is the intensity for corresponding wavelength at zero depth. Hence the adsorption spectrum Ia(λ) at the depth D can be determined as
Ia(λ) = I0(λ) · K(λ) · D (1)
where K(λ) is the adsorption by marine water as a function of wavelength.
The spectrum at the depth D will be equal to the spectrum on the surface I0(λ) minus the adsorption spectrum Ia(λ):
I(λ) = I0(λ) - Ia(λ),
or, by substituting (1) into this expression, we shall derive:
I(λ) = I0(λ) · (1 - K(λ) · D) (2)
From this expression we can derive the graph of light penetration into seawater d(λ):
d(λ) = (1 - I(λ) / I0(λ)) / K(λ)) (3)
Providing that the graph in Fig. 2 is based on the assumption that light intensity on the specified depth is equal to 1% of the intensity on the surface, i.e. I(λ) = 0,01 · I0(λ), we can simplify (3):
d(λ) = 0.99 / K(λ)
This function d(λ) is our graph of light penetration into seawater, which is pictured in Fig. 2. Using this graph we can determine light adsorption in seawater as a function of wavelength K(λ):
K(λ) = 0.99 / d(λ) (4)
By substituting the expression (4) into (2), we can derive the spectral distribution of light at a given depth D:
I(λ) = I0(λ) · (1 - 0.99 · D / d(λ)) (5)
where I0(λ) is the light spectrum on the surface and d(λ) is the graph of light penetration into seawater (Fig. 2).
Using the expression (5) and the data from graphs in Fig. 1 and Fig. 2, we can obtain the diagram of light energy distribution vs. wavelength at a given depth. As an example, on the same graph (Fig. 3) we pictured light's relative spectral distribution at the surface and at the depths of 5m (about 16.4 feet) and 15m (49 feet). Note: 15m is the maximum depth at which we can still find many light-demanding corals in nature. At the depths below 20m, the number of light demanding species sharply decreases.
Fig. 3 Light spectral distribution vs. wavelength on the surface (light blue), at 5m (blue) and 15m (dark blue) depths
The light-blue graph corresponds to irradiation on the surface, the blue graph - to 5m depth, and the dark-blue - to 15m depth. Note that with depth, the red part of the spectrum virtually disappears.
[B]During hundreds of millions years of evolution marine photosynthetic organisms adapted to best utilize mainly the violet and blue parts of the spectrum, which is more abundant in their environment, and are not very sensitive to the red spectrum (which, in contrast, is most actively utilized by terrestrial plants). Symbiotic zooxanthellae in marine photosynthetic organisms are primitive Pyrrophyta algae [5] containing mainly chlorophyll a and c and carotenoid pigments (peridinine, xanthins, etc) which exhibit strong absorption in the blue-green part of the spectrum. [6,7,22]. Fig. 4 [22] demonstrates light adsorption by zooxanthellae.[/B]
[B]Fig. 4 Light absorption by zooxanthellae
The horizontal axis is the wavelength, in nanometers, and vertical axis is adsorption, in arbitrary units. You can see from the graph that violet and blue colors strongly prevail over red (note that for red spectrum, the 660-680nm range is preferable).
Our main conclusion from the above is that violet and blue light are most important for marine photosynthetic organisms.[/B]
Knowing what is naturally available to corals from the color spectrum, we shall now consider the next important issue: how irradiation by different spectral ranges affects coral coloration?
Before we consider the influence of the light spectrum on coral coloration I would like to point out that even coloration of the same coral may vary significantly depending on conditions. Unfortunately, it is very difficult to provide exactly identical conditions for the corals, even in the same aquarium - and this is even harder for two different tanks. Without providing the right conditions for the corals, other attempts to improve their coloration, such as adjustments of the light spectrum, will be in vain[/QUOTE]
