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11 Applications of LEDs
The research of LED light source in the agricultural field is promising. Due to the
wide spectra coverage and compact size of LED, the device will be widely used in
agriculture in the future.
11.4.2 Alternative Plant Lighting
At present, the most commonly used artificial light source in greenhouse mainly
includes fluorescent lamps, high pressure sodium lamps, low pressure sodium lamps,
metal halide lamps and the like. The disadvantages of these light sources are high
energy consumption, and high operating costs. The energy costs accounting for
50–60% of the total operating costs. Therefore, improving luminous efficiency and
reducing energy consumption have always been an important issue in artificial light
applications in the agricultural field. Ordinary fluorescent lamps provide more green
light, about 50%. The rest part is mostly red and blue light, which account for about
25% of the total spectrum. The infrared spectrum is very low. Fluorescent lamps have
high luminous efficiency and long lifetime with up to about 12,000 h, but its power
is relatively small (28 and 36 W). Because the spectra of such light contain a lot of
green light, it is easy to cause crops to grow in vain. Therefore, such light is generally
used in plant tissue culture. The sodium lamp is a gas-emitting light source that emits
mercury and sodium vapor. Its luminescence spectrum is concentrated at 589 nm.
The luminous efficiency is as high as 120 lm/W. Standard operating sodium vapor
pressure of the lamp is about 10 kPa. There are more red orange light and less blue
green light in the luminescence spectrum. However, high-pressure sodium lamp is a
heat source. The surface temperature is high and the amount of heat generated during
operation is large. Therefore, the crop cannot be irradiated by such light source at
a close distance. Metal halide lamp is a gas illuminating light source in which a
mixed vapor of mercury and a rare metal halide generates an electric arc to discharge
light. Different spectra can be exhibited by changing the composition of the metal
halide. It has high luminous efficiency, high power and long lifetime between 5000
and 20,000 h. However, the filler in the lamp also contains mercury and will cause
pollution. Its spectrum contains a lot of infrared light, which generates a large amount
of heat and cannot illuminate the crop at close range. Most of the test light sources
use filters or colored polyvinyl chloride films to obtain light quality. It is impossible
to quantitatively and precisely modulate the spectral energy distribution and regulate
the light environment, thus affecting the reliability and comparability. For a long
time, the traditional artificial light source applied in the facility has uncontrollable
wavelength, high energy consumption and high operating cost, which has become
an obstacle to the development of application in the agricultural field.
Light has a regulating effect on photosynthesis, growth, morphogenesis and material metabolism of plants. At present, the light sources in greenhouses used to add up
more light are generally fluorescent lamps, high-pressure sodium lamps and incandescent lamps. Spectral energy diffusion is designed according to the needs of the
human eye for light. The spectrum required for plant growth is different from the
11 Applications of LEDs
The research of LED light source in the agricultural field is promising. Due to the
wide spectra coverage and compact size of LED, the device will be widely used in
agriculture in the future.
11.4.2 Alternative Plant Lighting
At present, the most commonly used artificial light source in greenhouse mainly
includes fluorescent lamps, high pressure sodium lamps, low pressure sodium lamps,
metal halide lamps and the like. The disadvantages of these light sources are high
energy consumption, and high operating costs. The energy costs accounting for
50–60% of the total operating costs. Therefore, improving luminous efficiency and
reducing energy consumption have always been an important issue in artificial light
applications in the agricultural field. Ordinary fluorescent lamps provide more green
light, about 50%. The rest part is mostly red and blue light, which account for about
25% of the total spectrum. The infrared spectrum is very low. Fluorescent lamps have
high luminous efficiency and long lifetime with up to about 12,000 h, but its power
is relatively small (28 and 36 W). Because the spectra of such light contain a lot of
green light, it is easy to cause crops to grow in vain. Therefore, such light is generally
used in plant tissue culture. The sodium lamp is a gas-emitting light source that emits
mercury and sodium vapor. Its luminescence spectrum is concentrated at 589 nm.
The luminous efficiency is as high as 120 lm/W. Standard operating sodium vapor
pressure of the lamp is about 10 kPa. There are more red orange light and less blue
green light in the luminescence spectrum. However, high-pressure sodium lamp is a
heat source. The surface temperature is high and the amount of heat generated during
operation is large. Therefore, the crop cannot be irradiated by such light source at
a close distance. Metal halide lamp is a gas illuminating light source in which a
mixed vapor of mercury and a rare metal halide generates an electric arc to discharge
light. Different spectra can be exhibited by changing the composition of the metal
halide. It has high luminous efficiency, high power and long lifetime between 5000
and 20,000 h. However, the filler in the lamp also contains mercury and will cause
pollution. Its spectrum contains a lot of infrared light, which generates a large amount
of heat and cannot illuminate the crop at close range. Most of the test light sources
use filters or colored polyvinyl chloride films to obtain light quality. It is impossible
to quantitatively and precisely modulate the spectral energy distribution and regulate
the light environment, thus affecting the reliability and comparability. For a long
time, the traditional artificial light source applied in the facility has uncontrollable
wavelength, high energy consumption and high operating cost, which has become
an obstacle to the development of application in the agricultural field.
Light has a regulating effect on photosynthesis, growth, morphogenesis and material metabolism of plants. At present, the light sources in greenhouses used to add up
more light are generally fluorescent lamps, high-pressure sodium lamps and incandescent lamps. Spectral energy diffusion is designed according to the needs of the
human eye for light. The spectrum required for plant growth is different from the