Luminous paint
As a luminous color is defined as a coating , the more visible light emits, as incident from the outside, that is, more than by directional or diffuse reflection as for reflectors would be possible. Luminous colors are colored with luminous pigments .
The energy required for this can be provided based on various physical principles:
- Fluorescent paint converts invisible UV light into visible light
- Afterglow paint stores energy that was absorbed during lighting and releases it again with a time delay
- Radioactive luminous paint , in which the energy comes directly or indirectly from the radioactive decay of a substance
Daylight colors
Daylight colors ( neon colors ) use fluorescence to convert the blue and near UV range of daylight into light of greater wavelength (blue-green, yellow and red are typical). Yellow and red are perceived much brighter by the eye with the same light intensity ( V-lambda curve of the sense of sight). In this way, a significant increase in contrast is achieved, especially in cloudy weather and at dusk (higher proportion of blue in daylight). The substances or effects used for this purpose are with the optical brighteners , as they are z. B. are found in detergents in a slightly lower proportion, identical.
Fluorescent colors are used in highlighters to highlight text passages on paper and as signal colors , for example in safety vests or warning surfaces on emergency services vehicles.
Fluorescent colors not only shine in daylight, but also especially under black light .
Afterglow colors
Afterglow colors (but not: "After t luminous colors") store incident light in the form of excitation energy and give it off with a time delay ( phosphorescence ). Most of these colors consist of alkaline earth sulfides (CaS, SrS or BaS) annealed in a reducing atmosphere with small amounts of foreign metals such as manganese.
Such afterglow inks are used to mark emergency exits and for various items of jewelery and decorative items (" glow-in-the-dark " products).
Radioactive luminous colors
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A radioactive luminescent paint always consists of a radioactive substance, previously mostly radium salt , later until a few years ago either a tritium compound or promethium salt , and a fluorescent substance such as zinc sulfide . The ionizing radiation stimulates the fluorescent substance ( luminescence ) .
The fluorescent substances used or other additional substances are often also capable of phosphorescence. Therefore - apart from permanent glow - after exposure to light a strong afterglow that decreases within seconds can be observed.
The direct radiation of the radioactive substances used today for luminous colors has a range of only a few centimeters in air, since only alpha emitters and low-energy beta emitters are used. Shielding is already achieved by a transparent cover. However, fluorescent paints can pose a risk of radiation if they crumble because the radioactive substance can then be incorporated . Older clock luminescent hands, dials and scales sometimes also contained radioactive substances with far-reaching radiation. These are particularly dangerous if the objects are constantly carried on the body.
In the past, the workers who painted the dials and moistened the brush with their mouths ( Radium Girls ) were particularly at risk . Cancer of the tongue and mandible was a widespread occupational disease among these workers, which eventually led to the awareness of the dangers of radiation.
In the second half of the 20th century, radioactive, radium-containing luminescent paint was used on a large scale by the military to make switches and controls recognizable in the dark. When health damage caused by military radar systems was publicized and investigated at the beginning of the 2000s , potential cancer diseases caused by luminous paints also came up for discussion in the German armed forces.
Similar techniques
- Retroreflection ( cat's eyes , reflector , reflector foil )
- Tritium gas light source - special light sources that glow for years without any energy supply
Web links
Individual evidence
- ↑ Damage to health from luminous paint. Der Spiegel, 32/2004.