Whether you grow indoors or simply need an additional light source, artificial lighting is a popular and relatively easy solution these days. Today we are going to discuss some of the more popular solutions in artificial lighting, but first we will answer the question: “What makes a good light source?”

As you can read in ‘Light & Plants, Part I – The Basics‘ and ‘Light & Plants, Part II – Hardcore Data‘, plants use certain colors of light to convert energy into a usable energy source (sugar). So the first thing a good light source should have at least the ones mainly used. Obviously the perfect light source will have them all. Another important quality a good light source should have is high luminous intensity*, thus the amount of energy reaching the plant and eventually converted is high. The last thing we need to remember when choosing a light source is cost. Usually artificial lighting means the use of electricity as an energy source, as with standard light bulbs. Electricity cost money, so a good light source will supply the right colors, will have high luminous intensity and of course will do all of that with as little electricity as possible. With the sun having all possible colors used by plants, extremely high luminous intensity, it’s no doubt the perfect light source and it can’t get any cheaper than free. It is perfect, but when that fails we need alternatives.

Incandescent Lamps

Incandescent lamps work on the Incandescence** principle and are possibly the most common type of light source used in private homes. Contrary to what you might think, incandescent lamps are not a good light source. They only contain some of the colors needed by plants, mostly from the red end of the spectrum and the Lumen/Wattage efficiency is relatively low. Meaning low luminous intensity and high cost.

Fluorescent Lamps

Fluorescent lamps are a type of gas-discharge lamps and also a common light source. With a wider spectrum and much more flexibility in producing certain wavelengths, the fluorescent lamps are a much better light source than incandescent ones. The relatively high Lumen/Wattage efficiency will help keep the costs low with only few actual shortcomings. The first one is the still not high enough luminous intensity, meaning the lamp should be kept as close as possible to the plant. This might not be a real disadvantage with seedlings, but the cost is quite high with most mature plants. Another one is the requirement of ballast, which limits the possible lamp designs. Compact versions (CFL) with ballast built-in are sold, so one could just use a standard lamp holder, but the cost of those lamps is usually higher.

High Intensity Discharge Lamps

High intensity discharge (HID) lamps are arc based. The actual conductor varies depending on the color temperature and luminous intensity sought for. HID lamps are quite popular in the industrial sector, especially as an alternative light source for plants. With one of the highest Lumen/Wattage efficiency out there, they’re probably the best artificial light you can find. The most notable HID lamps in agriculture are probably Metal Halide (MH) and High Pressure Sodium (HPS), with the MH leaning more to the blue end of the spectrum and HPS to the red one. Like the fluorescent lamps, they also require ballast. Some even require special conditions for them to operate. Indeed, HID need much care in terms of investment, but they’re worth it.

Light Emitting Diodes

Light Emitting Diodes (LED) are semiconductor based solid state diodes. They are very common in electronics and as indicator lights. The current Lumen/Wattage efficiency is not enough to compete with some of the other solutions, but this recently hyped light source has its advantages. A possibility to replicate the wavelengths plants need is one of them. With the right components, it is possible to create an array with most possibly the best artificial spectrum. Another advantage is the lack of moving parts, something that influences the life span and usage for the better. The technology is still underdeveloped, but future developments should improve overall efficiency. For now it is not your best choice, even though it is a good one.

* Luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI*** unit of luminous intensity is the candela (cd), an SI base unit.

** Incandescence is the release of electromagnetic radiation, usually visible radiation, from a body due to its temperature.

*** International System of Units

See Also:
Light & Plants Part I - The Basics
Light & Plants Part II - Hardcore Data

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Photosynthetic Activity

The light receiving photosynthetic pigments in the plant are at the thylakoid membrane in the chloroplasts. The most common pigment in his quantity and is present in all green plants and alga is ‘Chlorophyll a’. Other pigments are called secondary pigments and include ‘Chlorophyll b’ and carotenoids. To every photosynthetic pigment a typical absorption spectrum, meaning a different absorption ability of light in different wavelengths.

• Chlorophyll a – 420nm, 663nm
• Chlorophyll b – 453nm, 645nm
• Carotenoids – 420nm-480nm

The light receiving pigments array constructs a type of antenna that is used to transfer light energy to the reaction center (Chlorophyll a), which drives the light process in Photosynthesis. The quantitative ratio of different chlorophylls varies in different plants, organs at the same plant, different exterior conditions and different periods.

The absorption by the chlorophyll is mainly obvious in the red and blue-violet area, although absorption lines in other areas do exist. Chlorophylls a and b are separated by the wavelength at which maximum absorption occurs. The absorption lines of Chlorophyll a at both the blue and red ends of the spectrum are farther away than the absorption lines of Chlorophyll b. Chlorophyll quantities in a green leaf vary between 0.05%-0.2% of the fresh weight. The ratio between Chlorophyll a and Chlorophyll b is 2.5/1=a/b, although it is not permanent because Chlorophyll a is more easily destroyed, meaning the quantitative ratio varies under different conditions.

Types of Plants

Sun and shade plants differ by various leaf qualities due to the amounts of light reaching them. Shade plants allocate more resources to harvest light than CO2 fixation. This is why in shade plants the secondary pigments are produced in greater quantities – more Chlorophyll and less RuBisCO*.

* Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as sucrose.

See Also:
Light & Plants Part I - The Basics
Artificial Light

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Light & Plants

Light is one of the most basic requirements for the existence of plants.
The energy source of plants is sugar. Instead of consuming it like almost any other life form, plants create their food in a process called Photosynthesis.
For this process to occur, the plant needs water, carbon dioxide (CO2) and sunlight which is the energy converted and stored in the sugar.

Types of Light

The white light contains various colors in it, just like demonstrated in a rainbow. Different colors of sunlight can be seen in different parts of the world and even different times of the day. Plants react differently to various colors of light, and actually use only some of them in Photosynthesis. The main colors of light used by plants are red and blue. High concentration of red light is manifested in yellow-orange light and with blue, white-bright blue light.

Light color is labeled as color temperature. The color temperature of a light source is determined by comparing its chromaticity with a theoretical, heated black-body radiator. The temperature (in Kelvin) at which the heated black-body radiator matches the color of the light source is that source’s color temperature.

See Also:
Light & Plants Part II - Hardcore Data
Artificial Light

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