Krypton

Krypton is a colourless, odourless, and tasteless noble gas that occupies Group 18 of the periodic table. It is chemically inert under standard conditions and occurs in trace amounts in the Earth’s atmosphere. Though relatively rare, krypton possesses unique physical and spectroscopic properties that have enabled its use in lighting, imaging, and scientific research. While it is not a common household substance, its applications in industry, technology, and science are notable for their precision and effectiveness.

Physical and Chemical Characteristics

Krypton (chemical symbol Kr, atomic number 36) was discovered in 1898 by British chemists Sir William Ramsay and Morris Travers during their investigations into liquefied air. It was identified as one of the noble gases, extracted through fractional distillation of liquid air. The gas has a density approximately three times that of air and a boiling point of −153.4 °C, which makes it easily separable from other atmospheric components under cryogenic conditions.
Chemically, krypton is largely inert due to its complete valence electron shell. However, under extreme conditions, it can form a few stable compounds, such as krypton difluoride (KrF₂), discovered in 1963. This mild reactivity distinguishes it slightly from lighter noble gases like helium and neon. Krypton also emits a distinctive whitish-blue light when subjected to electrical discharge, a property that underpins many of its practical applications.

Discovery and Natural Occurrence

The discovery of krypton was part of the broader exploration of atmospheric gases in the late nineteenth century. Ramsay and Travers isolated it after evaporating almost all components of liquid air, noticing a faint spectral line that revealed the presence of a previously unknown element. The name “krypton” originates from the Greek word kryptos, meaning “hidden,” reflecting its elusive presence in the atmosphere.
Krypton constitutes about 1 part per million (ppm) of the Earth’s atmosphere. It is commercially obtained by the fractional distillation of liquid air, alongside other noble gases such as neon, argon, and xenon. Although present in minute quantities, modern cryogenic separation techniques have made large-scale production feasible, particularly for industrial and scientific purposes.

Everyday and Consumer Applications

In everyday life, krypton is most commonly encountered through its use in lighting. Krypton gas is used in certain high-performance light bulbs, such as krypton-filled incandescent lamps and flash photography bulbs, where it helps to prolong filament life and enhance luminous efficiency. Compared with argon, krypton’s lower thermal conductivity allows for a smaller filament and brighter light output, resulting in more efficient bulbs.
Krypton arc lamps are employed in film projectors, slide projectors, and high-intensity searchlights due to their bright white light that closely resembles natural daylight. Similarly, krypton fluorescent lamps are used in areas where accurate colour rendering is essential, such as in photography studios and scientific laboratories.
In combination with halogen gases, krypton contributes to the production of krypton-halogen bulbs, widely used in vehicle headlamps, stage lighting, and portable torches. These lamps produce bright, focused beams and have longer lifespans than traditional incandescent bulbs, improving energy efficiency and visual performance.

Industrial and Technological Applications

Krypton plays a valuable role in a number of specialised industrial and scientific applications. Its stable and inert properties make it ideal for use in controlled environments and high-precision instruments.
One of the most important industrial uses of krypton lies in laser technology. Krypton is a component of krypton-ion lasers, which emit visible light across multiple wavelengths, notably red and green. These lasers are used in holography, spectroscopy, and laser displays, as well as in medical treatments such as retinal photocoagulation for repairing detached retinas. The krypton fluoride (KrF) excimer laser, in particular, has found significant applications in semiconductor manufacturing and refractive eye surgery (LASIK) due to its ultraviolet emission at 248 nanometres.
In the window and insulation industry, krypton gas is employed as a filling material between panes of high-performance double or triple-glazed windows. Its low thermal conductivity reduces heat transfer more effectively than air or argon, improving energy efficiency in buildings. Krypton-filled glazing units are particularly used in climates with extreme temperatures and in architectural designs prioritising insulation and energy conservation.
In scientific measurement, krypton once served as the standard for the definition of the metre. Between 1960 and 1983, the metre was defined in terms of the wavelength of radiation emitted by the isotope krypton-86. Although later replaced by a definition based on the speed of light, this historical role underscores krypton’s importance in precision metrology.

Economic Significance and Market Factors

The global market for krypton is relatively small compared to other industrial gases, owing to its rarity and specialised applications. Nevertheless, its economic value is high because of the limited availability and the technical sophistication of its uses. Krypton is mainly produced as a by-product in large-scale air separation plants that also generate oxygen, nitrogen, and argon.
The price of krypton fluctuates depending on demand from sectors such as lighting, aerospace, and electronics. With the growing shift from conventional lighting to energy-efficient LED and laser systems, demand for krypton in traditional lamp manufacturing has declined. However, its continued use in high-end optical, medical, and scientific equipment maintains its market relevance.
Countries with major industrial gas production facilities—such as the United States, Russia, and China—dominate krypton supply. Recycling and recovery of krypton from manufacturing processes have become increasingly important in reducing costs and ensuring supply stability.

Environmental and Safety Considerations

Krypton is non-toxic, non-flammable, and chemically inert, posing minimal direct health or environmental hazards. In enclosed environments, however, it can displace oxygen, potentially causing asphyxiation if leaks occur in confined spaces—though such risks are uncommon and easily managed with standard ventilation practices.
The environmental footprint of krypton extraction primarily arises from the energy-intensive nature of cryogenic distillation used to separate atmospheric gases. Nonetheless, improvements in industrial efficiency and gas recovery systems have mitigated these impacts. Krypton does not contribute to atmospheric pollution, ozone depletion, or global warming.

Advanced and Emerging Applications

Krypton’s use continues to evolve with technological progress. In advanced aerospace propulsion systems, krypton is being explored as an alternative propellant for ion thrusters, particularly in low-cost satellite missions. Though xenon is more efficient, krypton offers a less expensive option with sufficient performance for small satellite applications.
In scientific research, krypton isotopes play a role in nuclear and environmental studies. Krypton-85, a radioactive isotope, is used as a tracer for monitoring air and water movement and detecting nuclear fuel reprocessing activities. Stable isotopes of krypton assist in dating ancient groundwater and ice cores, providing valuable insights into climate change and geological processes.

Overall Significance

Although krypton is a rare and largely invisible component of the atmosphere, its influence extends across lighting, energy conservation, precision measurement, and cutting-edge technology. From the glow of camera flashes to the precision of laser surgery and satellite propulsion, krypton’s applications highlight the enduring importance of rare gases in modern industrial and scientific advancement. Its combination of inertness, luminosity, and thermal properties ensures that krypton, though hidden by nature, continues to illuminate and enhance human innovation.