Abstract: A system may include one or both of a light emitter and a light receiver. The system may include an optical filter adjacent one or both of the light emitter or the light receiver. The optical filter includes a wavelength selective scattering layer. The wavelength selective scattering layer may have a near-infrared scattering ratio of less than about 0.9. The filter may have a visible reflective haze ratio of greater than about 0.5. A method may include disposing the wavelength selective scattering layer adjacent one or both of the light emitter and the light receiver. An article may include the optical filter. The wavelength selective scattering layer may have an average near-infrared scattering of less than 60%, an average visible scattering of greater than 10%, and a difference between the % total visible reflectance and the % diffuse visible reflectance of less than 20.

Abstract: A respiratory mask assembly (10), adapted to be placed over the nose and mouth of the face of a wearer. The mask assembly includes a base mask (12), defining a set of openings; a filter (30), detachably supported by the base mask and covering the openings; and a source of electricity (60). Also, an air exit valve (34) is positioned over one of the openings of the base mask and releases air from inside the mask to the outside when pressure inside is greater than air pressure outside. Finally, a centrifugal fan (22) is electrically connected to the source of electricity and is positioned in one of the openings of the base mask so as to draw air through the filter to the inside. This fan blows air into the inside in a direction that misses the wearer's face.

Abstract: A respiratory mask assembly (10), adapted to be placed over the nose and mouth of the face of a wearer. The mask assembly includes a base mask (12), defining a set of openings; a filter (30), detachably supported by the base mask and covering the openings; and a source of electricity (60). Also, an air exit valve (34) is positioned over one of the openings of the base mask and releases air from inside the mask to the outside when pressure inside is greater than air pressure outside. Finally, a centrifugal fan (22) is electrically connected to the source of electricity and is positioned in one of the openings of the base mask so as to draw air through the filter to the inside. This fan blows air into the inside in a direction that misses the wearer's face.

Abstract: A respiratory mask assembly (10), adapted to be placed over the nose and mouth of the face of a wearer. The mask assembly includes a base mask (12), defining a set of openings; a filter (30), detachably supported by the base mask and covering the openings; and a source of electricity (60). Also, an air exit valve (34) is positioned over one of the openings of the base mask and releases air from inside the mask to the outside when pressure inside is greater than air pressure outside. Finally, a centrifugal fan (22) is electrically connected to the source of electricity and is positioned in one of the openings of the base mask so as to draw air through the filter to the inside. This fan blows air into the inside in a direction that misses the wearer's face.