Light: Illuminated!
Light: Illuminated!
Before we can understand light… we need to understand light. What is it? How does it work? Will it cook me dinner? The answers to these are pretty simple, really. Light, by definition, is simply a segment of electromagnetic radiation which is visible to our eyes. In the case of our applications for providing energy for photosynthetic inhabitants we widen the realms a bit into spectrums we can’t actually see – Ultraviolet and Infrared – but the meat of the action happens where our eyes can see it (approximately 400nm to 700nm, or violet through to red). Within those 300 short nanometres happens everything you’ve ever seen with your naked eyes and will ever conceivably get to see. And yes, if you use it properly, it will in fact cook you dinner.
Photosynthesis, it’s also quite simple. Certain components of a photosynthetic creature’s makeup (pigments) are activated by luminous radiation (ie. Light) and use it to produce useful energy. It’s literally synthesis by photons, hence the name. While all visible light is what can be considered Photosynthetically Active Radiation (PAR), different pigments will be attuned to different parts of the visible spectrum the most readily. For instance, Chlorophyll b, one of the most common pigments in corals, has reception peaks around 450nm (primary) and 650nm (secondary), whereas β-Carotene, another common pigment, has peaks around 445nm (primary) and 480nm (secondary). Because of it, the spectra we employ to illuminate our tanks are of vital importance. More on that later.
Now… all of this photosynthesis action doesn’t happen without the intensity to actually drive the reaction. So, we run into three conditions linked to the amount of photons being used (Photosynthetically Usable Radiation, or PUR) – Photocompensation, Photosaturation, and Photoinhibition. These mean the need to compensate for insufficient luminous radiation, the peak/optimal usage of luminous radiation, and a surplus of luminous radiation respectively.
Under the first condition, there simply is not enough PUR available for photosynthesis to occur and so the process is offset via another form of energy. This is quite taxing on the animal and is a condition which leaves energy being produced in the least efficient state.
The second condition, Photosaturation, now this is the butter zone. This is what we want to aim for. Under this condition, the amount of PUR is the most optimal for photosynthesis, as it allows the peak production of energy. The animal is at its optimal state and light is being converted most efficiently. Or, to put it another way, the animal is as satisfied as it possibly can be in the conditions.
Thirdly, Photoinhibition. This one is a very nasty one. This simply means there’s too much PUR being provided and it’s overrunning the animal with luminous intensity. In the case of coral specifically, this is a bad thing as it can result in what’s known as zooxanthellae bailout. This bailout is when the symbiant zooxanthellae physically eject from the coral as a means of protecting itself from potential mortality. This can quite easily lead to death of the host and is a condition which also has a negative impact on your wallet to sustain such unnecessary levels of photointensity.
Now, how exactly do we measure this luminous intensity? The unit most regularly used to quantify this is Photosynthetic Photon Flux Density (PPFD), measured in µmol/m2/sec, or, the amount of photons falling over 1 m2 in one second. While this doesn’t directly become useful for aquarists because it’s a rather meaningless measurement without context, when given points for comparison it’s rather useful. From this we can optimise our lighting to match our inhabitants as closely as possible. In having said that, along with sufficient levels of PPFD, we have to ensure a reasonable spread of intensity across the wavelengths for what we’re keeping.
Light for our tank is generally given an arbitrary number to rate the colour it produces. For example, the most common in reefkeeping is around the 10000K mark, or, in lay terms, what would be described as a cool White. Where do these numbers come from? It’s a relation to what is called the emission spectrum of a Black body radiator, an idealised body which absorbs all incidental electromagnetic radiation. The spectrum of our lights is related to the point which a Black body would best suit, and given the associated rating (a Correlated Colour Temperature, or CCT). The most commonly available “full spectrum” (having a spectrum which is supposedly wide-band, not isolated to a single range) ratings are 10000K, 14000K, and 20000K. Respectively these are described as cool White, crisp White, and Blue – cool being marginally bluer than midday sunshine in higher latitudes (most of the continental US will have a midday sunlight temperature around 7500-8000K); crisp being bluer again than the cool which means there’s a greater emphasis on the blue wavelengths; and the blue is the bluest commonly available spectrum which is very little other spectrum than simply blue and violet wavelengths.
From a growth perspective, with a relative intensity the same, 10000K should offer the greatest growth potential of these three types of light. Because it’s a wider band spectrum and offers plenty of red-end light, there’s no wastage of wavelengths and excitation of more pigment response peaks. This, pound for pound, should offer the highest growth rates for most corals. 20000K will typically offer the best formation of strong colouration in corals as it tends to have stronger intensity in the blue/violet end where many chromoproteins are developed. 14000K is a good trade-off of this.
A good baseline for a mixed aquarium to be able to sustain a range of livestock at or around photosaturation should be considered as around 100 µmol/m2/sec at the base of the aquarium. This will allow most deeper-water lagoonal species to maintain photosaturation at the bottom of the tank, and ensure with proper placement, things such as Acroporidae and Pocilloporidae will be above their photocompensation points. For most systems there is no benefit to running more light than this, however a tank strictly comprised of reefcrest species would probably benefit from a minimum of around 250-300 µmol/m2/sec based on studied photosaturation points in such.
There’s a lot more to the story when it comes to light, but for now this should be a fairly good basis to get you going. It can be daunting and scary at first, but once you understand the fundamental principles it all makes a lot more sense. Happy reefing!
Before we can understand light… we need to understand light. What is it? How does it work? Will it cook me dinner? The answers to these are pretty simple, really. Light, by definition, is simply a segment of electromagnetic radiation which is visible to our eyes. In the case of our applications for providing energy for photosynthetic inhabitants we widen the realms a bit into spectrums we can’t actually see – Ultraviolet and Infrared – but the meat of the action happens where our eyes can see it (approximately 400nm to 700nm, or violet through to red). Within those 300 short nanometres happens everything you’ve ever seen with your naked eyes and will ever conceivably get to see. And yes, if you use it properly, it will in fact cook you dinner.
Photosynthesis, it’s also quite simple. Certain components of a photosynthetic creature’s makeup (pigments) are activated by luminous radiation (ie. Light) and use it to produce useful energy. It’s literally synthesis by photons, hence the name. While all visible light is what can be considered Photosynthetically Active Radiation (PAR), different pigments will be attuned to different parts of the visible spectrum the most readily. For instance, Chlorophyll b, one of the most common pigments in corals, has reception peaks around 450nm (primary) and 650nm (secondary), whereas β-Carotene, another common pigment, has peaks around 445nm (primary) and 480nm (secondary). Because of it, the spectra we employ to illuminate our tanks are of vital importance. More on that later.
Now… all of this photosynthesis action doesn’t happen without the intensity to actually drive the reaction. So, we run into three conditions linked to the amount of photons being used (Photosynthetically Usable Radiation, or PUR) – Photocompensation, Photosaturation, and Photoinhibition. These mean the need to compensate for insufficient luminous radiation, the peak/optimal usage of luminous radiation, and a surplus of luminous radiation respectively.
Under the first condition, there simply is not enough PUR available for photosynthesis to occur and so the process is offset via another form of energy. This is quite taxing on the animal and is a condition which leaves energy being produced in the least efficient state.
The second condition, Photosaturation, now this is the butter zone. This is what we want to aim for. Under this condition, the amount of PUR is the most optimal for photosynthesis, as it allows the peak production of energy. The animal is at its optimal state and light is being converted most efficiently. Or, to put it another way, the animal is as satisfied as it possibly can be in the conditions.
Thirdly, Photoinhibition. This one is a very nasty one. This simply means there’s too much PUR being provided and it’s overrunning the animal with luminous intensity. In the case of coral specifically, this is a bad thing as it can result in what’s known as zooxanthellae bailout. This bailout is when the symbiant zooxanthellae physically eject from the coral as a means of protecting itself from potential mortality. This can quite easily lead to death of the host and is a condition which also has a negative impact on your wallet to sustain such unnecessary levels of photointensity.
Now, how exactly do we measure this luminous intensity? The unit most regularly used to quantify this is Photosynthetic Photon Flux Density (PPFD), measured in µmol/m2/sec, or, the amount of photons falling over 1 m2 in one second. While this doesn’t directly become useful for aquarists because it’s a rather meaningless measurement without context, when given points for comparison it’s rather useful. From this we can optimise our lighting to match our inhabitants as closely as possible. In having said that, along with sufficient levels of PPFD, we have to ensure a reasonable spread of intensity across the wavelengths for what we’re keeping.
Light for our tank is generally given an arbitrary number to rate the colour it produces. For example, the most common in reefkeeping is around the 10000K mark, or, in lay terms, what would be described as a cool White. Where do these numbers come from? It’s a relation to what is called the emission spectrum of a Black body radiator, an idealised body which absorbs all incidental electromagnetic radiation. The spectrum of our lights is related to the point which a Black body would best suit, and given the associated rating (a Correlated Colour Temperature, or CCT). The most commonly available “full spectrum” (having a spectrum which is supposedly wide-band, not isolated to a single range) ratings are 10000K, 14000K, and 20000K. Respectively these are described as cool White, crisp White, and Blue – cool being marginally bluer than midday sunshine in higher latitudes (most of the continental US will have a midday sunlight temperature around 7500-8000K); crisp being bluer again than the cool which means there’s a greater emphasis on the blue wavelengths; and the blue is the bluest commonly available spectrum which is very little other spectrum than simply blue and violet wavelengths.
From a growth perspective, with a relative intensity the same, 10000K should offer the greatest growth potential of these three types of light. Because it’s a wider band spectrum and offers plenty of red-end light, there’s no wastage of wavelengths and excitation of more pigment response peaks. This, pound for pound, should offer the highest growth rates for most corals. 20000K will typically offer the best formation of strong colouration in corals as it tends to have stronger intensity in the blue/violet end where many chromoproteins are developed. 14000K is a good trade-off of this.
A good baseline for a mixed aquarium to be able to sustain a range of livestock at or around photosaturation should be considered as around 100 µmol/m2/sec at the base of the aquarium. This will allow most deeper-water lagoonal species to maintain photosaturation at the bottom of the tank, and ensure with proper placement, things such as Acroporidae and Pocilloporidae will be above their photocompensation points. For most systems there is no benefit to running more light than this, however a tank strictly comprised of reefcrest species would probably benefit from a minimum of around 250-300 µmol/m2/sec based on studied photosaturation points in such.
There’s a lot more to the story when it comes to light, but for now this should be a fairly good basis to get you going. It can be daunting and scary at first, but once you understand the fundamental principles it all makes a lot more sense. Happy reefing!
