Lightstick
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A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. The outer plastic tube contains one part of the chemical mixture, and the inner compartment is a glass or brittle plastic tube containing the second mixture. If the lightstick is bent, the inner tube breaks and the chemicals mix, resulting in a reaction that emits light but not necessarily heat. This phenomenon is called chemoluminescence.
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[edit] Usage
Lightsticks have various purposes: they are used in the military, by recreational divers doing night diving, by marching band conductors for night time performances, and also used for entertainment at parties (especially raves), concerts, and dance clubs. Glowsticking refers to the use of glowsticks in dancing. A further application are light effects, especially balloon-carried light effects.
By adjusting the concentrations of the two chemicals, manufacturers can produce lightsticks that either glow brightly for a short amount of time, or glow more dimly for a much longer amount of time. At maximum concentration (typically only found in laboratory settings), mixing the chemicals results in a furious reaction, producing large amounts of light for only a few seconds.
Heating a lightstick causes the reaction to proceed faster and the lightstick to glow brighter, but for a shorter period of time. Cooling a lightstick slows the reaction and causes it to last longer, but the light is dimmer. This can be demonstrated by refrigerating or freezing an active glowstick; when it warms up again, it will resume glowing .
When punctured, glowsticks can also be used as pens to write messages that can only be seen in the dark.
[edit] Chemistry
The light stick contains two chemicals and a suitable fluorescent dye (sensitizer, or fluorophor). The chemicals in the plastic tube are a mixture of the dye and a derivate of phenyl oxalate ester (also called Cyalume). The chemical inside the glass vial is concentrated (about 35%) hydrogen peroxide. By mixing the peroxide with the phenyl oxalate ester, a chemical reaction takes place; the ester is oxidized, yielding two molecules of phenol and one molecule of peroxyacid ester. The peroxyacid decomposes spontaneously to carbon dioxide, releasing energy that excites the dye, which then deexcites by releasing a photon. The wavelength of the photon depends on the structure of the dye; eg. 9,10-bis(phenylethynyl)anthracene gives green light, 9,10-diphenylanthracene yields blue light, 5,6,11,12-tetraphenylnaphthacene yields red light. Other colors can be made of combination of dyes, eg. purple requires three dyes.
Other chemicals are usually present in the mixture as well; eg. sodium salicylate as a catalyst, and Bis(2-ethylhexyl) phthalate (DEHP) as a solvent.
Instead of cyalume, bis(2,4,5-trichlorophenyl-6-carbopentoxyphenyl)oxalate (CPPO) is used in practical formulations, as it gives significantly better quantum yield.
A similar reaction can be achieved with bis(2,4,6-trichlorophenyl)oxalate (TCPO).
The dyes used in lightsticks usually exhibit fluorescence when exposed to ultraviolet radiation. Therefore even a spent lightstick will shine under a black light.
[edit] Fluorophors used
- 9,10-diphenylanthracene (DPA) emits blue light
- 1-chloro-9,10-diphenylanthracene (1-chloro(DPA)) and 1-chloro-9,10-diphenylanthracene (2-chloro(DPA)) emit blue-green light with higher efficiency than unsubstituted DPA, dihydro(DPA) is purple [1]
- 9,10-bis(phenylethynyl)anthracene (BPEA) emits green light
- 1-chloro-9,10-bis(phenylethynyl)anthracene emits yellow-green light, used in 30-minute high-intensity Cyalume sticks
- 2-chloro-9,10-bis(phenylethynyl)anthracene emits green light, used in 12-hour low-intensity Cyalume sticks
- 1,8-dichloro-9,10-bis(phenylethynyl)anthracene emits yellow light, used in Cyalume sticks
- Rubrene emits orange-red light.
- 2,4-di-tert-butylphenyl 1,4,5,8-tetracarboxynaphthalene diamide emits deep red light, together with DPA is used to produce white or hot-pink light, depending on their ratio
 9,10-diphenylanthracene yields blue light |
 9,10-bis(phenylethynyl) anthracene yields green light |
 1-chloro- 9,10-bis(phenylethynyl) anthracene yields yellow light |
 rubrene (5,6,11,12-tetraphenyl naphthacene) yields yellow light |
 5,12-bis(phenylethynyl) naphthacene yields orange light |
 Rhodamine 6G yields orange light |
 Rhodamine B yields red light |
[edit] History
Cyalume was invented by Michael M. Rauhut and Laszlo J. Bollyky of American Cyanamid based on work by Edwin A. Chandross of Bell Labs. 1
Other early work on chemoluminescence was carried out at the same time, by researchers under Herbert Richter at China Lake Naval Weapons Center. 2 3
[edit] See also
[edit] External links
| Lighting and Lamps
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|---|---|---|
| Incandescent: | Conventional - Halogen - Parabolic aluminized reflector (PAR) |  |
| Fluorescent: | Compact fluorescent (CFL) - Linear fluorescent - Induction lamp | |
| Gas discharge: | High-intensity discharge (HID) - Mercury-vapor - Metal-halide - Neon - Sodium vapor | |
| Electric arc: | Arc lamp - HMI - Xenon arc - Yablochkov candle | |
| Combustion: | Acetylene/Carbide - Candle - Gas lighting - Kerosene lamp - Limelight - Oil lamp - Safety lamp | |
| Other types: | Sulfur lamp - Light-emitting diode (LED) - Fiber optics - Plasma | |
