Artificial sunlight is the use of a

light source Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terah ...

to simulate sunlight where the unique characteristics of sunlight are needed, but where sufficient natural sunlight is unavailable or infeasible. A device used to simulate sunlight is a solar simulator.

Composition of natural sunlight

The spectrum of

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...

striking the

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...

is 100 to 1,000,000 nanometers (nm). This can be divided into five regions in increasing order of

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

s: *

Ultraviolet C Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...

(UVC) range: 100–290 nm *

Ultraviolet B Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

(UVB) range: 290–320 nm *

Ultraviolet A Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

(UVA) range: 320–400 nm * Visible range or

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

: 400–700 nm *

Infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

range. It is further divided into three types on the basis of wavelength: ** Infrared-A: 700–1,400 nm ** Infrared-B: 1,400–3,000 nm ** Infrared-C: 3,000–1,000,000 nm

Applications

Illumination

It has been claimed that artificial light-sources whose spectra most closely mimic the spectrum of terrestrial sunlight are good for human health and productivity. Such sources give

full-spectrum light Full-spectrum light is light that covers the electromagnetic spectrum from infrared to near-ultraviolet, or all wavelengths that are useful to plant or animal life; in particular, sunlight is considered full spectrum, even though the solar spectral ...

Light therapy

Artificial sunlight is useful in treating and preventing

seasonal affective disorder Seasonal affective disorder (SAD) is a mood disorder subset, in which people who have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year. Common symptoms include sleeping too much, having li ...

(also known as ''winter depression'', which causes depression symptoms specifically in winter), and

delayed sleep phase syndrome Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is a delaying of a person's circadian rhythm (biological clock) compared to those of societal norms. The diso ...

, in which the circadian rhythm (the rhythmic alternation between daylight and nighttime behavior and bodily states) is disturbed and the person falls asleep much later than he or she wants. Artificial sunlight may also be useful in reducing the severity of

jet lag Jet lag is a physiological condition that results from alterations to the body's circadian rhythms caused by rapid long-distance trans-meridian (east–west or west–east) travel. For example, someone flying from New York to London, i.e. from ...

Aquarium lighting

Different

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s in a

reef aquarium A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical coral reef environment. A reef aquarium requires appropriatel ...

require different lighting conditions. Most corals depend

symbiotically Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''S ...

, a type of

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

. The zooxanthellae require light to perform photosynthesis, and they provide the coral

polyps A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end i ...

with

simple carbohydrates Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. They are usually colorless, water-solub ...

. A technique employing light-emitting diodes (LEDs) allows

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

control of the parameters of lighting, such as warmth and coolness of color, which facilitates the simulation of daybreak, sunset, and

lunar phases Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...

. Some animals, such as the

red-eared slider The red-eared slider or red-eared terrapin (''Trachemys scripta elegans'') is a subspecies of the pond slider (''Trachemys scripta''), a semiaquatic turtle belonging to the family Emydidae. It is the most popular pet turtle in the United States, ...

turtle, also benefit from such aquarium lights.

Product testing

Testing the efficacy of sunscreens requires the use of solar simulators. Manufacturers of

solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.

s must test the overall efficiency of the cells. They require to be tested indoors, which has traditionally been performed using mostly Sulphur plasma lamps or

xenon arc lamp A xenon arc lamp is a highly specialized type of gas discharge lamp, an electric light that produces light by passing electricity through ionized xenon gas at high pressure. It produces a bright white light to simulate sunlight, with application ...

. Within the automotive industry, solar simulation tests are used to ensure automotive system reliability and functionality. Artificial sunlight (solar simulators) are also used for sun light exposure testing and of ''color fastness'' and ''material stability'' for textile, plastics and paints.

References

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