Abstract: In anti-glare spectacles comprising a frame and a pair of lenses, each lens comprises a substantially circular central zone of substantially complete transparency and an adjoining light-absorbing annular zone over an angular range of substantially 45.degree. in which the light absorption increases sharply from the inside of the annulus and drops towards the outside of the annulus by the square of the angle. An outer zone of each lens has a low absorption.

Abstract: A tubular measuring chamber (3) is described for temporarily holding alveolar breath for determining the quantity of alcohol in the breath of infra red radiation absorption. The radiation path length between an I.R. source (1, 2) and a condenser lens (7) and detector (8) is made a multiple of the actual length of the tube by bending the tube in any convenient way e.g. a helix (FIG. 1 and FIG. 3), a serpentine (FIG. 2), or meanderingly with definite bends (FIGS. 4-7).The internal surface of the tube (3) is made highly reflective to I.R. and plane reflectors (10) are located at definite bends in the tube or between different sections of tube (see FIGS. 4-7), to deflect radiation from one tube section to the next.A saliva trap and mouthpiece (6) to receive the breath is connected mid-way along the tube (3) between the radiation source (1, 2) and condenser (7).

Abstract: A device for measuring concentration of a gas adapted to be used for measuring the concentration of alcohol molecules in exhaled breath. The device relies for its operation on the known phenomenon that radiation is absorbed by different materials at different characteristic wavelengths. Radiation of a wavelength which will be absorbed by the gas to be tested is focused into the end of a tube the internal surface of which is highly polished or formed with a layer of material which is totally internally reflecting at the wavelength used and a radiation detector is located at the opposite end of the tube.Partly to increase the path length by causing many internal reflections to occur and partly to reduce the overall size of the device, the tube is curved either in the form of a helix with constant or varying radius of curvature or is curved first one and then the next in a serpentine fashion.

Abstract: A device as described whereby the concentration of a gas such as alcohol vapor can be measured using radiation absorption techniques in a chamber. The chamber is an elongated tube having a window at one end through which infra red radiation can pass with an optical reflector at the two ends of the tube and at least one other reflector for causing the reflected radiation to leave the tube through a second window in the side of the tube, from where it passes to a detector.Sensitivity is increased by passing the radiation in series through a number of parallel arranged chambers which conveniently are located within a common housing.