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Engineering Materials
Published in Leo Alting, Geoffrey Boothroyd, Manufacturing Engineering Processes, 2020
Leo Alting, Geoffrey Boothroyd
Glasses are generally based on silica (SiO2) with additives that alter the structure or reduce the melting point. Presently there are some 750 different types of commercially available glasses, ranging from window glass, bottles, and cookware to types with special mechanical, electrical, high-temperature, chemical, or optical characteristics. All glasses contain at least 50% silica, known as a glass former. By adding oxides of aluminum, sodium, calcium, barium, and so on, properties, with the exception of strength, can be modified greatly.
Vision
Published in Anne McLaughlin, Richard Pak, Designing Displays for Older Adults, 2020
Most people are already familiar with the effects of aging on vision. We may have an older relative or parent who is experiencing difficulties or we may have experienced them ourselves. The most familiar stereotype of an older person is one who wears bifocal glasses. Bifocal glasses contain two levels of correction; one for near and one for far vision. The need to wear bifocals, triggered by the gradual loss in the ability to alter the shape of the intraocular lens for different distances (“presbyopia”), may be the most easily recognizable age-related visual change; however, there are other, more subtle changes that affect a user’s ability to read a display.
Optical Materials
Published in Christoph Gerhard, Optics Manufacturing, 2018
As already mentioned above, there are two main types of optical glasses, crown glass and flint glass. The classification is based on the Abbe number. Crown glasses feature an Abbe number higher than 50 (Ve > 50 → crown glasses) whereas the Abbe number of flint glasses is lower than 50 (Ve < 50 → flint glasses). The classification of optical glasses is usually visualized and identified by the so-called Abbe diagram (glass map or “n vs. V diagram”). Here, the index of refraction (nd or ne, respectively) is plotted vs. the Abbe number (Vd or Ve, respectively) as shown in Figure 3.11.
Photobiology eye safety for horticultural LED lighting: Transmittance performance of eyewear protection using high-irradiant monochromatic LEDs
Published in Journal of Occupational and Environmental Hygiene, 2018
The transmittance performances of the tested eyewear protections at an irradiance level of 1000 W·m−2 using monochromatic LED assemblies (Experiment 1) are shown in Table 2 and Figure 5. Overall, each type of tested eyewear protection exhibited distinct transmittance performances. The mean transmittance percentage was 1.77% for the welding glasses, 13.12% for the polarized glasses, 15.27% for the safety goggles, and 27.65% for the sunglasses. The welding goggles had the lowest transmittance percentages among all the tested glasses in this study, which were approximately between 0.1 and 9.5% (Table 2). The percent light-reductions of the welding goggles were at least 95%, except the welding goggles (sample 1 from Table 1) under the 735 nm LED assembly, which was around 90%. Note that the transmittance data examined using the 405 and 447.5 nm LED assemblies are not shown in Table 2 since the irradiance levels penetrating the glasses were detected as zero by the pyranometer. As for the sunglasses and polarized glasses, they both had low UV light transmittance (< 10%) but the polarized glasses had better light-reduction performance than the sunglasses for the rest of the tested wavelengths (447–735 nm), especially under the 735 nm LED light. With the 405 nm LED light, the percentage transmittance for both types of glasses was between 0.1–10%. The mean transmittance percentages were 15 and 30% for the sunglasses and polarized glasses, respectively, between 447 and 655 nm. For the 735 nm LED light, the transmittance percentages were ∼35% for the polarized glasses and ∼90% for the sunglasses.