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Lighting = food for plants
Well, not exactly but this is a simple way to understand. All plants (aquatic and terrestrial) use light source to convert Carbon Dioxide (CO2) and water (H2O) into Glucose/energy (food) which is needed for plant growth
CO2 + H2O + Sunlight energy (from Chlorophylls or Carotenoids) -> Glucose + O2
The above process is called Photosynthesis. The actual process is a lot more complicated than that but for easier understanding, we will spare the technical details but approach this topic from layman point of view.
All plants either use chlorophylls (green pigment) or carotenoids (yellow/orange/red pigment) to trap light source and use it to break down water (H2O) into Hydrogen (H) and Oxygen (O2), hydrogen is subsequently combined with Carbon Dioxide (CO2) to form glucose, which is a form of energy use in all living cells, for both plants and animals. O2 is released as a by-product during photosynthesis process.
In nature, light source is provided by sunlight. However, in a planted tank, which is normally indoor, we need to provide light source which emits the lights that can be used by the plants for photosynthesis process.
A) Wavelength (Spectrum)
White light is made of different wavelengths (colors) or we can call it spectrums of light. Wavelengths are measured in nanometers (nm) and the lights that are visible to our eyes range from 380nm to 700nm. At one end of this visible light spectrum is Ultraviolet (UV), which has a wavelength between 300-350nm.
The other end of this visible spectrum is Infra Red (IR) light with 700-750nm.
| Colors
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Violet
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Deep Blue |
Blue |
Green
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Yellow
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Orange
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Red |
| Wavelength (nm)
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<300
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300-400 |
400+ |
500+
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550-600
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600+
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700+
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Different sources of lights (Sunlight, tungsten light bulb, fluorescence tubes, Metal-halide etc) produce different light spectrum. In general, lights with shorter wavelength are more “powerful”, thus, having higher penetration rate. Lights with longer wavelength are less “energetic” and having lower penetration power. For example, UV lights can penetrate deeper into water with ease as compare to the IR lights, in another words, UV lights are more readily available for aquatic plants in nature as compare to IR lights.
Due to this behavior of lights, aquatic plants has adjusted themselves accordingly to maximize the efficiency during photosynthesis, meaning, aquatic plants will have more sensitivity to red lights for photosynthesis as compare to UV lights, because in nature, lesser red lights are available in the water. Therefore to capitalize on the limited amount of red light, aquatic plants need to increase the photosynthetic sensitivity towards it.
Selecting the suitable light spectrum is one of the most important factors in planted tank lighting, because only the right spectrum can give the plant what it needs for the growth.
B) Lighting Output (Wattage)
Lighting output for planted tank is normally measured in wattage. However, how much wattage is insufficient, enough or too much for certain size/volume of aquarium is very often a debatable subject. Some planted tank hobbyist use 2 Watts per Gallon (WPG) or 0.5 Watts per Liter as guideline, but it is very common we see hobbyist use much lesser or higher wattage for their tank, there is no rules set in stone.
The actual plants need is PAR (Photosynthetically Active Radiation) which is function of Lux and Spectrum. Unfortunately there is no simple way to measure PAR. You need expensive gadget to do so which not easily accesible by most hobbyist. To make matter worst light tube/bulb packaging does not even mention about spectrum. Most of the time you can only see wattage and lumen (1 lux = 1 lumen per square meter). For simplicity we have to satisfy with watt although it is far from ideal.
How much lighting output is suitable for a planted tank, is very much depending on the following factors:
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Types of plants – whether it is a light demanding plants or otherwise. Some plants excel in high lighting condition but some can do equally well in both high and low lights.
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CO2 level – Tank with higher lighting output will need higher CO2 level. You need to lower the wattage if you do not plan to inject CO2
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Nutrient level – Tank with high lighting output will need higher nutrient level. Same as above, lower the wattage if no plan to add fertilizer
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Algae – Algae (sometime) can be use as an indicative for lighting output. If Algae is rampant in a tank, it is possible that balance between Lighting, CO2 and Nutrient has not been reached. High lighting output is not a direct factor for algae, but we normally reduce lighting when we have algae problem because it is a sign that CO2/nutrient is insufficient in relation to the excess in lighting. By reducing the light we are removing those limits.
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Tank depth – deeper tank requires higher output than shallow tank.
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Tank size – bigger the tank require higher lighting output.
As mentioned earlier, there is no fix rule in selecting lighting output for planted aquarium, but to provide a simple guide for beginner, the following can be use as reference:
1) 30cm tank : 15-25w
2) 60cm tank: 50-100w
3) 90cm tank: 100-200w
Please take note that the above is just a very rough guide, advance planted tank keeper may use much lesser or more light than stated above
C) Lighting hours
Apart from wattage, lighting hours or photo-period is also an important factor in planted tank. How many hours of lighting is enough, insufficient or too much for a planted tank, is also depending on the few factors mentioned above. A rough guideline would be 8-10 hours a day.
D) Color Temperature (K)
Another aspect of light which is commonly being considered in planted tank is the color temperature, measure in K (Kelvin). Lower color temperatures are “warmer” lights which is more yellowish to reddish. Higher color temperatures are “cooler” lights which is more bluish to whitish.
The following table gives a better understanding of color temperature in relation to different light source:
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Temperature
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Source
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1,700 K
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Match flame
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1,850 K
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Candle flame
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2,700–3,300 K
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Incandescent light bulb
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3,350 K
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Studio "CP" light
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3,400 K
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Studio lamps, photofloods, etc.
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4,100 K
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Moonlight, xenon arc lamp
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5,000 K
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Horizon daylight
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5,500–6,000 K
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Typical daylight, electronic flash
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6,500 K
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Daylight, overcast
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9,300 K
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CRT screen
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Plants get sunlight in nature, therefore in planted aquarium, we should provide lighting source that is as close to the characteristic of sunlight as possible. Using the above table as reference, the color temperature of the light source we choose for planted aquarium should be around the range of 6000k to 10,000k, these are the common range suitable for aquatic plants.
E) Common light source for planted Aquarium
The most common light sources for planted tanks are
Fluorescent lights - one of the most cost effective (economical) options. Most common types are T8, T5, PL,
PLL and others. It has a life span of about 2 years but it is advisable to replaceafter 1 year due to decrease in output efficiency after the 1st year.
Metal Halide (MH) - one of the most effective (and expensive) choice, intense and high lighting outputs. Most suitable for deep aquarium, 2 ft (60cm) or more.
LED - the latest addition to the aquarium lighting family
Sunlight - not recomended for newbie becuase it is intense and difficult to control tank parameter to support it.
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PL |
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Normally use in Aquarium but slowly replace by T5 |
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T8 |
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Normally known as fluorescence light. Slowly replace by T5 |
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T5 |
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Look similar to T8 only thinner and more energy efficient
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MH (HQI) |
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Very bright, point source thus can create nice ripple effect, good for > 2 ft (60 cm) deep tank |
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LED |
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New technology, can create ripple effect, efficient but very expensive at the moment |
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Sunlight |
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Free, but difficult to control. Not advisable for newbie
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Personal view from Robert:
The difficult part about lighting probably knowing how many watt for particular tank size. If you search around website you will find that plants are able to adapt in wide range of light condition. However, the question still the same, how much is enough. The problem is because lighting is complex, we need to consider about spectrum and intensity. Most if not all light bulb in the market does not mention these information in their packaging. Make matter worst, it require special equipment to measure it and it isn't cheap. Not to mention different plant have different light requirement.
To save my self a trouble, normally put as much as light can be fit on top of the tank. This save me from issue such us foreground plant grow tall or stem plant grow leggy. However in high light condition without proper nutrient and CO2 management, algae will take over in no time.
One important factor that hobyist forget is light reflector. It is part of the light set that you can go without. With proper light reflector, you can increase the light intensity reaching the surface by more than 1.5. My recomendation is to get light set with individual reflector.
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