- Light is defined in physics as an electromagnetic wave that has a wavelength between 380 and 780 nanometers. That's the part of the electromagnetic radiation that we humans can see. (1 nanometer = 0.000000001 meters)
- Electric and magnetic fields create a light particle, a so-called photon, which moves at the speed of light (300,000 kilometers per second) and has wavelength-dependent energy.
- E = hc / [lambda] with E = energy, h = plank's constant of action, c = speed of light and [lambda] = wavelength
- The shorter the wavelength, the higher the energy of the electromagnetic radiation.
- The following picture shows the visible light spectrum:
Light in general
- Light is the visible part of electromagnetic radiation with wavelengths between 380 and 780 nanometers.
- Electromagnetic radiation having a proportionately increasing with decreasing wavelength energy.
- Other areas of electromagnetic radiation and their significance are listed below.
It makes bones visible for the diagnosis of injuries
|5 picometers to 10 nanometers|
|UV radiation||It is responsible for the formation of vital vitamins (D3 & K2) in humans, but also for sunburn with too much UV radiation||100 to 380 nanometers|
|Infrared radiation||Invisible heat radiation that has a multitude of uses. Among other things, the Internet is being realized with IR radiation around 1550nm in glass fibers.||780 nm to 1 mm|
|Microwaves||The microwave heats food with water very efficiently because it uses electromagnetic radiation close to the resonance frequency of the dipole molecule water||1 mm to 300 mm|
|WLAN||Used for fast data transmission via radio||about 12 centimeters|
- We humans can absorb light with our eyes, process it into a picture and thus capture our environment three-dimensionally and interact with it. Blind people alone are not able to survive in the wild.
- Electromagnetic radiation in higher amounts can be harmful to us. For example: UV radiation causes sunburn, gamma radiation kills cells and mobile phone radiation is suspected of triggering brain tumors.
- We can perceive colors with the help of different 3 different color receptors. A light source illuminates its light spectrum onto an object, which reflects light into the eye with its reflection spectrum:
- The electromagnetic solar radiation is the energy source of our planet and the origin of our life. Various firing processes make it so incredibly powerful.
- The light spectrum of the sun, which arrives at the earth ground, is not always the same. During the day it changes from warm white to cold white (noon) to warm white. In addition, the light spectrum depends on the position on the ground and the current weather.
- The light spectrum of the sun outside the earth's atmosphere and in different weather conditions at one point:
Light and plants
- People eat energy through their food (calories) and grow. Plants can use the energy of solar radiation for growing through photosynthesis
- In photosynthesis, energy-poor molecules are transformed into high-energy molecules by the energy of light
- CO2 is used and oxygen is generated
Plant secondary metabolism is very important to plants and some can contribute to photosynthesis and other metabolic processes in the plant. Unlike chlorophylls, however, secondary metabolites are not vital to the plant. They are available in electron transport chains in various processes important for homeostasis in plant growth. Carotenoids make plants stronger against pests. E.g.: carotenoids, phytochromes, xenophylls
- Chlorophylls are color pigments that give plants their green color which, after receiving electromagnetic radiation of a particular wavelength, can to a certain probability produce energy for plant growth. Chlorophylls are the most important source of energy for plants and vital for plants.
- There are several different chlorophylls and bacteriophyllophylls, which are slightly different. Chlorophyll a and b are particularly relevant for plant growth.
- The absorption spectra of Cholophyll a and b are shown here:
Carotenoids have a different action spectrum compared to chlorophylls. The metabolic process can contribute energy to photosynthesis, but also to changes in the plant that are very important for pest resistance.
- 1 µmol of radiation means about 60,220,000,000,000,000 individual photons with wavelengths of the light spectrum of a lamp. A single sol lamp emits about 150 ,mol per second. 12 hours are 43,200 seconds - it's easy to imagine how complex plant growth is.
- Every single photon can be absorbed with certain probability in one of the myriad molecules of the plant, it should hit the plant and trigger a certain metabolic process
- The countless number of metabolic processes results statistically in an energetic homeostasis, which determines the quality of plant growth.
- Radiation outside of the PAR, here over 700nm contributes to the metabolic processes in the plant. The phytochrome system is important for detecting the daylength of plants. By controlling the ratio between 660nm and 730nm, the growth of a plant can be influenced.
- If too little 730nm radiation is present, the metabolic processes of the plants can come in an "energetic congestion", which limits the plant growth per watt (energy).
- The phytochrome system consists of two molecules, which under irradiation with 680nm (P) in the form Pr passes. If the form Pr is irradiated with 730 nm radiation, the reversible process is reversed.
- The plant "senses" the R: FR ratio and thus the time of day by the phytochrome ratio Pr: Pfr.
- The R: FR ratio changes during the day: At early dawn and in the sunset, the ratio R: FR is less than 1, while it is significantly less than 1 during the day.
- With the help of the phytochrome system, the growth of plants can be influenced morphologically and qualitatively with spectral impulses.
[Spectra Pr and Pfr]
Terms in lighting technology
- Watt is the basic physical energy unit. The energy of a photon can be calculated by the wavelength of the photon, the speed of light at which the photon travels, and a constant value (Planck's constant).
- The energy of a photon decreases in proportion to the wavelength. A red photon with 660nm has 50% less energy than a blue photon with 440nm.
- µmol is an indication of the number of photons of a lamp. 1 µmol is about 60,220,000,000,000,000 single photons, but that does not say anything about how much energy each photon has.
- The color temperature is white light color, which most closely corresponds to the spectral ratio of the radiation of a blackbody. It is measured in Kelvin [K], the temperature of the correlating blackbody.
- The sun has a temperature of about 5700K
- The light spectrum of the sun fluctuates during the day on Earth between 2500-12000K, depending on the time of day or sun position.
- PAR (photosynthetically active radiation) is by definition electromagnetic radiation with wavelength between 400-700nm.
- The PAR value has only limited validity: Green radiation around 550nm is not as efficiently absorbed by a plant as red or blue radiation.
- The PAR value contains neither UV radiation nor deep red radiation with 730nm, which are important for plant growth.
- The PPFD is the photon flux density in these areas and is measured in µmol / m²s, ie in photons per square meter per second.
- The PBAR is the "photobiologically active radiation" and extends the PAR of 280-800nm wavelength. It takes into account important UV, FR and IR radiation.
Technology - Artificial light
- What efficiency means must first be defined. Ultimately, there are several factors that contribute to the overall quality of a product.
- Electro-Optical Efficiency: The conversion of electrical energy to electromagnetic radiation has an efficiency between 0-100%. Typically, one NDL has 25%, one LED about 40% (strongly manufacturing temperature and material dependent)
- Sustainable efficiency: The radiation decreases with lifetime. At lower temperatures, LEDs age more slowly than at high temperatures.
- PAR / W or µmol / J is the number of photons (400-700nm) emitted per electrical energy. This value decreases with aging of the lamp and says little about the quality of a luminaire.
- Current flow in doped semiconductors excites electrons to a higher but unstable energy level. When the electrons fall back down to the initial level, the energy is emitted in the form of light.
- The light color of the LEDs is determined by the doping and the material of the semiconductor. The width (half width) of the spectrum of an LED normally varies by about 30nm.
- White LEDs are usually realized with blue LEDs that shine through a phosphor and partially excite it. Then broadband (about 200nm bandwidth) radiation of low energy is emitted. The blue radiation of the LEDs and the green-red radiation of the phosphor add up to a white light. In the meantime, there are also red phosphors in the plant lighting segment that do not emit green radiation.
- By applying a voltage, particles are excited in a gas mixture, which emit light. The efficiency of high-pressure gas discharge lamps is max. approx. 25% (Cf. LED approx. 40-45%)
- The light spectrum is determined by the gas mixture and can not be determined as easily as with LEDs.
- As a result, the efficiency of the gas discharge lamps (yield per watt) is significantly lower than with LEDs.