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New glass lets in light not heat
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Does your office feel like a greenhouse in summer? Take heart: researchers in Australia are developing a new kind of glass that lets sunlight through but blocks much of its heat.
Stefan Schelm and Geoff Smith of the University of Technology in Sydney have developed a cheap polymer that, laminated between glass sheets, cuts out the warming wavelengths, which are just below that of red light1. Viewed at an oblique angle, it has a slight bluish haze. Otherwise, it appears transparent, with a hint of green.
Existing solar-control glazing is either expensive or unsatisfactory in appearance. Costly versions contain layers of ultrathin silver, which absorbs infrared. Cheaper alternatives feature infrared-absorbing pigments or dyes that get broken down by strong sunlight or scatter light, giving laminated glass a smoky haze.
The new laminate's key ingredient is a compound called lanthanum hexaboride, denoted LaB6, which absorbs near-infrared radiation. Grains of LaB6 just 20-200 millionths of a millimetre across are dispersed in plastic sheeting that is sandwiched in glass.
The particles, being smaller than the wavelength of visible light, don't scatter sunlight strongly. Moreover, they are sprinkled very sparsely within the plastic, leaving it highly transparent.
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June 30th, 2003
Source: Nature.com |
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