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Artificial white light may become eye-friendly

Oct. 6, 2010
Courtesy of the Institute of Physical Chemistry 
of the Polish Academy of Sciences
and World Science staff

The harsh, ar­ti­fi­cial-looking light of to­day’s energy-ef­fi­cient light bulbs could be­come a thing of the past—re­placed by nat­u­ral-looking light, a group of sci­en­tists says.

The Pol­ish chem­ists claim to have found a class of sub­stances that make light which mim­ics sun­light in that its spec­trum fea­tures a con­tin­u­ous blend of al­most all vis­i­ble col­ors. This is si­m­i­lar to the way sun­light is formed. In con­trast, con­ven­tion­al energy-ef­fi­cient bulbs such as flu­o­res­cent lamps and LED’s emit on­ly a hand­ful of spe­cif­ic col­ors. 

Bottles of a newly de­scribed, light-emitting sub­stance next to a small toy. Pol­ish chem­ists claim to have found a class of com­pounds that make light which mim­ics sun­light in that its spec­trum fea­tures a con­tin­u­ous blend of al­most all vis­i­ble col­ors. How­ever, the light emitted is not in­tense en­ough to be use­ful in every­day products yet, they say. (Im­age cou­rtesy IPC PAS, Grze­gorz Krzy­zew­ski)
Ei­ther way, the col­ors com­bine to cre­ate white or whit­ish light, but in the sec­ond case the far more lim­it­ed range of col­ors leads to a deader qual­ity.

The new dis­cov­ery in­volves “a class of or­gan­ic mol­e­cules emitting white light with con­tin­u­ous spec­trum cov­er­ing al­most the en­tire vis­i­ble [col­or] range,” ex­plained Jer­zy Kar­piuk of the Pol­ish Acad­e­my of Sci­ences’ In­sti­tute of Phys­i­cal Chem­is­try, who heads the re­search team.

Karpiuk stressed that it may be a long time be­fore the find­ings lead to a use­ful prod­uct, part­ly be­cause the light pro­duced is weak. None­the­less, the fact that it took on­ly one, sim­ple chem­i­cal to gen­er­ate the white light is en­cour­ag­ing, he added.

White is a spe­cial col­or cre­ated as a re­sult of mix­ing of light waves of all col­ors, or in sci­en­tif­ic par­lance, wave­lengths. “Wave­length” lit­er­al­ly means the length of the light wave re­quired to cre­ate each spe­cif­ic col­or—the dis­tance be­tween neigh­bor­ing wave peaks. Vis­i­ble light comes from col­ors in the wave­length range from about 420 to 730 mil­lionths of a mil­li­me­ter.

The white from flu­o­res­cent lamps and si­m­i­lar ar­ti­fi­cial sources is cre­ated by the mix­ture of three col­ors: red, green and blue. These come main­ly from emis­sions of spe­cif­ic hues from sub­stances known as lu­min­o­phores. It takes sev­er­al sub­stances to ge­ner­ate the light, mak­ing the prod­ucts less ef­fi­cient and harder to pro­duce, ac­cord­ing to Karpiuk and col­leagues.

Karpiuk’s group worked with crys­tal vi­o­let lac­tone, a sub­stance pro­duced in mass quan­ti­ties and used in copy pa­per as a so-called dye pre­cur­sor. A mol­e­cule of it in­cludes two struc­tures called flu­o­ro­phores that emit light: one blue, the oth­er or­ange. But mem­bers of the re­search team found that by mod­i­fy­ing the way that the mol­e­cule is en­er­get­ic­al­ly stim­u­lat­ed, var­y­ing hues can be emitted, to the point that a con­tin­u­ous spec­trum and white light emerges.

Yet crys­tal vi­o­late lac­tone al­so has prop­er­ties that make it un­ suit­a­ble for real-life use as a light source, the re­search­ers said: the light is weak and light sources based on the mol­e­cule probab­ly can’t be ef­fi­cient­ly mass-pro­duced. 

“How­ever, the most im­por­tant thing is that we man­aged to show that a cer­tain con­cept works in prac­tice,” Kar­piuk said; it’s “on­ly a mat­ter of time be­fore light sources recre­at­ing nat­u­ral white light will be con­struct­ed.” The find­ings are pub­lished in the re­search jour­nal Phys­i­cal Chem­is­try Chem­i­cal Phys­ics.

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The harsh, artificial-looking light of today’s energy-efficient light bulbs could become a thing of the past—replaced by natural-looking light from similar ly efficient lamps, a group of scientists said. The Polish chemists claim to have found a class of substances that make light which mimics sunlight in that its spectrum features a continuous blend of almost all visible colors. This is similar to the way sunlight is formed. In contrast, conventional energy-efficient bulbs such as fluorescent lamps and LED’s emit on ly a handful of specific colors. Either way, the colors combine to create white or whitish light, but in the second case the far more limited range of colors leads to a deader quality. The new discovery involves “a class of organic molecules emitting white light with continuous spectrum covering almost the entire visible [color] range,” explained Jerzy Karpiuk of the Polish Academy of Sciences’ Institute of Physical Chemistry, who heads the research team. Karpiuk stressed that it may be a long time before the findings lead to a useful product, part ly because the light produced is weak. Nonetheless, the fact that it took on ly one, simple chemical to generate the white light is encouraging, he added. White is a special color created as a result of mixing of light waves of all colors, or in scientific parlance, wavelengths. “Wavelength” literal ly refers to the length of the light wave required to create each specific color—the distance between neighboring wave peaks. Visible light comes from colors in the wavelength range from about 420 to 730 nanometres, one nanometer being a millionth of a millimeter. The white from fluorescent lamps and similar artificial sources is created by the mixture of on ly three colours: red, green and blue. These come main ly from emissions of very specific hues from substances known as luminophores. It takes several substances to produce the light, making the products less efficient and harder to produce, according to Karpiuk and colleagues. Karpiuk’s group worked with crystal violet lactone, a substance produced in mass quanti ties and used in copy paper as a so-called dye precursor. A molecule of it includes two structures called fluorophores that emit light: one blue, the other orange. But members of the research team found that by modifying the way that the molecule is energetic al ly stimulated, varying hues can be emitted, to the point that a continuous spectrum and white light emerges. Yet crystal violate lactone also has properties that make it un suitable for real-life use as a light source, the researchers said: the light is weak and light sources based on the molecule probab ly can’t be efficient ly mass-produced. “However, the most important thing is that we managed to show that a certain concept works in practice,” Karpiuk said. “Now we are sure that it is on ly a matter of time before light sources recreating natural white light will be constructed.” The findings are publisheed in the research journal Physical Chemistry Chemical Physics.