Infrared (IR) light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 0.74 micrometres (µm) to 300 µm. This range of wavelengths corresponds to a frequency range of approximately 1 to 400 THz, and includes most of the thermal radiation emitted by objects near room temperature. Infrared light is emitted or absorbed by molecules when they change their rotational-vibrational movements.
The existence of infrared radiation was first discovered in 1800 by astronomer William Herschel. He made an instrument called a spectrometer to measure the magnitude of radiant power at different wavelengths. This instrument was made from three pieces. The first was a prism to catch the sunlight and direct and disperse the colors down onto a table, the second was a small panel of cardboard with a slit wide enough for only a single color to pass through it and finally, three mercury-in-glass thermometers. Through his experiment Herschel found that red light had the highest degree of temperature change in the light spectrum, however, infrared heating was not commonly used until World War II. During World War II infrared heating became more widely used and recognized. The main applications were in the metal finishing fields, particularly in the curing and drying of paints and lacquers on military equipment. Banks of lamp bulbs were used very successfully but by today’s standards, the power intensities were very low. The technique offered much faster drying times than the fuel convection ovens of the time. Production bottlenecks were mitigated and military supplies to the armed forces were maintained. After World War II the adoption of infrared heating techniques continued but on a much slower basis. In the mid 1950s the motor vehicle industry began to show interest in the capabilities of infrared for paint curing and a number of production line infrared tunnels came into use.
Properties of infrared rays and the infrared light
Much of the energy from the Sun arrives on Earth in the form of infrared radiation. Sunlight at zenith provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation. The balance between absorbed and emitted infrared radiation has a critical effect on the Earth’s climate. Infrared light is used in industrial, scientific, and medical applications. Night-vision devices using infrared illumination allow people or animals to be observed without the observer being detected. In astronomy, imaging at infrared wavelengths allows observation of objects obscured by interstellar dust. Infrared imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatus. Infrared imaging is used extensively for military and civilian purposes.
Military applications include target acquisition, surveillance, night vision, homing and tracking. Non-military uses include thermal efficiency analysis, environmental monitoring, industrial facility inspections, remote temperature sensing, short-ranged wireless communication, spectroscopy, and weather forecasting. Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space, such as molecular clouds; detect objects such as planets, and to view highly red-shifted objects from the early days of the universe. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm (micrometers), as shown by Wien’s displacement law. At the atomic level, infrared energy elicits vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared energy range, based on their frequency and intensity.
Curative effect of infrared rays
- help for normalization of high blood pressure, improve and stabilize blood circulation; a beneficial effect on pain in dorsal area and muscles, studs, bronchitis, asthmatic disorders;
- help with colds, fatigue and exhaustion of the human body;
- useful in inflammation of ears, nose and throat;
- reduce pain in arthritic and rheumatic diseases, in herniated disc too;
- facilitate kidney function;
- in stress situations;
- in procedures for the reduction of cellulite and fat digestion;
Areas of Use
Infrared radiation can be used as a heating source. Several studies have looked at using infrared saunas in the treatment of chronic health problems, such as high blood pressure, congestive heart failure and rheumatoid arthritis, and found some evidence of benefit. For example it is used in infrared saunas to heat the occupants, and also to remove ice from the wings of aircraft (de-icing). Far infrared is also gaining popularity as a safe heat therapy method of natural health care and physiotherapy. Infrared can be used in cooking and heating food as it predominantly heats the opaque, absorbent objects, rather than the air around them. Infrared heating is also becoming more popular in industrial manufacturing processes, e.g. curing of coatings, forming of plastics, annealing, plastic welding, print drying. In these applications, infrared heaters replace convection ovens and contact heating. Infrared heaters produce heat that is a product of invisible light and they consist of three parts: infrared light bulbs, a heat exchanger and a fan that blows air onto the exchanger to disperse the heat. Efficiency is achieved by matching the wavelength of the infrared heater to the absorption characteristics of the material. Infrared heaters are commonly used in infrared modules (or emitter banks) combining several heaters to achieve larger heated areas. Infrared heaters are usually classified by the wavelength they emit: Near infrared (NIR) or short-wave infrared heaters operate at high filament temperatures above 1800 °C and when arranged in a field reach high power densities of some hundreds of kW/m2. Their peak wavelength is well below the absorption spectrum for water, making them unsuitable for many drying applications. They are well suited for heating of silica where a deep penetration is needed. Medium-wave and carbon (CIR) infrared heaters operate at filament temperatures of around 1000 °C. They reach maximum power densities of up to 60 kW/m2 (medium-wave) and 150 kW/m2 (CIR). Far infrared emitters (FIR) are typically used in the so-called low-temperature far infrared saunas. These constitute only the higher and more expensive range of the market of infrared sauna. Instead of using carbon, quartz or high watt ceramic emitters, which emit near and medium infrared radiation, heat and light, far infrared emitters use low watt ceramic plates that remain cold, while still emitting far infrared radiation.
Infrared rays penetrate the skin up to 3-4 mm, they warm human body and mainly the skin by stimulating blood circulation, consequently the supply of nutrients and oxygen to the skin cells improves significantly hence the overall condition of the skin. By warming skin deep, increases the secretion of sweat. As a result of this process accelerates the release of dead cells appear to harmful toxins from the body, helps in weight loss, improves ease of digestion of fatty tissue, skin pores open and purify many easier and faster, and acquires increased skin elasticity and smoothness. Under constant exposure to infrared radiation largely reducing the occurrence of various skin problems, such as dandruff, acne, blackheads, etc. Infrared rays procedures are applied in a treatment of psoriasis, eczema, smoothing of wrinkles, joint diseases, skin injuries, etc.
Infrared rays and massage
In massage is often used initially warming with infrared heat. The infrared rays warm skin directly and relax the muscles, which favors quality massage. Warmed muscle and tissue lead to relaxation of the body and this kind of massage has a lasting and effective effect. Thanks to the massage blood circulation improves, stress and fatigue reduce, concentration increases, all processes in the body accelerate = improved health.
IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants. These devices usually conform to standards published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for remote controls to command appliances. Infrared remote control protocols like RC-5, SIRC, are used to communicate with infrared.
In infrared photography, infrared filters are used to capture the near-infrared spectrum. Digital cameras often use infrared blockers. Cheaper digital cameras and camera phones have less effective filters and can “see” intense near-infrared, appearing as a bright purple-white color. This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image. There is also a technique called ‘T-ray’ imaging, which is imaging using far-infrared or terahertz radiation. Lack of bright sources makes terahertz photography technically more challenging than most other infrared imaging techniques. Recently T-ray imaging has been of considerable interest due to a number of new developments such as terahertz time-domain spectroscopy.
Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of optical astronomy. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium.