Luminous paint
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Luminous paint (or luminescent paint) is paint that emits visible light through fluorescence, phosphorescence, or radioluminescence.
Fluorescent paint
The fluorescent chemicals in fluorescent paint absorb the invisible UV radiation, then emit the energy as longer
Fluorescent paints are made in both 'visible' and 'invisible' types. Visible fluorescent paint also has ordinary visible light pigments, so under white light it appears a particular color, and the color just appears enhanced brilliantly under black lights. Invisible fluorescent paints appear transparent or pale under daytime lighting, but will glow under UV light. Since patterns painted with this type are invisible under ordinary visible light, they can be used to create a variety of clever effects.
Both types of fluorescent painting benefit when used within a contrasting ambiance of clean, matte-black backgrounds and borders. Such a "black out" effect will minimize other awareness, so cultivating the peculiar luminescence of UV fluorescence. Both types of paints have extensive application where artistic lighting effects are desired, particularly in "black box" entertainments and environments such as theaters, bars, shrines, etc. The effective wattage needed to light larger empty spaces increases, with narrow-band light such as UV wavelengths being rapidly scattered in outdoor environments.
Phosphorescent paint
, and typically glows a pale green to greenish-blue color. The mechanism for producing light is similar to that of fluorescent paint, but the emission of visible light persists long after it has been exposed to light. Phosphorescent paints have a sustained glow which lasts for up to 12 hours after exposure to light, fading over time.This type of paint has been used to mark escape paths in aircraft and for decorative use such as "stars" applied to walls and ceilings. It is an alternative to radioluminescent paint.
When applied as a paint or a more sophisticated coating (e.g. a thermal barrier coating), phosphorescence can be used for temperature detection or degradation measurements known as phosphor thermometry.
Radioluminescent paint
Radioluminescent paint is a self-luminous paint that consists of a small amount of a
Because of safety concerns and tighter regulation, consumer products such as clocks and watches now increasingly use phosphorescent rather than radioluminescent substances. Previously radioluminicesent paints were used extensively on watch and clock dials and known colloquially to watchmakers as "clunk".[1] Radioluminescent paint may still be preferred in specialist applications, such as diving watches.[2]
Radium
Radioluminescent paint was invented in 1908 by
Radium paint used zinc sulfide phosphor, usually trace metal doped with an activator, such as copper (for green light), silver (blue-green), and more rarely copper-magnesium (for yellow-orange light). The phosphor degrades relatively fast and the dials lose luminosity in several years to a few decades; clocks and other devices available from antique shops and other sources therefore are not luminous any more. However, due to the long 1600 year half-life of the Ra-226 isotope they are still radioactive and can be identified with a Geiger counter.
The dials can be renovated by application of a very thin layer of fresh phosphor, without the radium content (with the original material still acting as the energy source); the phosphor layer has to be thin due to the light self-absorption in the material.
Promethium
In the second half of the 20th century, radium was progressively replaced with promethium-147. Promethium is only a relatively low-energy beta-emitter, which, unlike alpha emitters, does not degrade the phosphor lattice and the luminosity of the material does not degrade as fast. Promethium-based paints are significantly safer than radium, but the half-life of 147Pm is only 2.62 years and therefore it is not suitable for long-life applications.
Promethium-based paint was used to illuminate Apollo Lunar Module electrical switch tips, the Apollo command and service module hatch and EVA handles, and control panels of the Lunar Roving Vehicle.[4][5]
Tritium
The latest generation of the radioluminescent materials is based on
Tritium light sources are most often seen as "permanent" illumination for the hands of
Tritium lights are also found in some old rotary dial telephones, though due to their age they no longer produce a useful amount of light.
See also
- ChromaFlair
- Bioluminescence
- Chemiluminescence
- Historical aspects of luminous paint, Scientific American, "Luminous Paint", 10-Dec-1881, pp.368
References
- ^ "Radioactive luminous radium paint".
- ^ Hazards from luminised timepieces in watch/clock repair Archived 2011-07-04 at the Wayback Machine, UK Health and Safety Executive
- ^ a b "Radium paint takes its inventor's life; Dr. Sabin A. von Sochocky Ill a Long Time, Poisoned by Watch Dial Luminant. 13 Blood Transfusions. Death Due to Aplastic Anemia-- Women Workers Who Were Stricken Sued Company". The New York Times. 15 November 1928.
- ^ "Apollo Experience Report – Protection Against Radiation" (PDF). NASA. Archived from the original (PDF) on 14 November 2014. Retrieved 9 December 2011.
- ^ "CSM/LM Lighting" (PDF). NASA. Retrieved 11 April 2022.