DEVICE FOR ALERTING A MOTORIST TO THE DANGER OF ICED ROADS

摘要

1134026 Temperature indicators W DABISCH 17 May 1967 [17 May 1966] 23001/67 Heading G1D [Also in Division G2] An ice warning device for road safety purposes comprises Christiansen optical filter 1, the colour of the spectral transmission of which changes within the region of the freezing point of water and a reflector 2 for light from vehicle headlights, which has passed through the filter. The Christiansen filter comprises powdered glass disposed in a fluid medium and this acts as a dispersion filter unless the filter is at the temperature at which the refractive indices of the glass and the fluid are the same when coloured light having a certain bandwidth in the spectrum will pass through the filter. The colour of this light changes over a temperature range around the above mentioned temperature. Sintable materials for the filter are given as examples in the Specification and the arrangement is such that the spectral transmission of the filter and therefore the colour of light reflected, after passage through the filter, back to the driver of the vehicle at the freezing point of water, is of a distinctive colour which is recognizable by the driver. A glass filter 3 may be disposed in front of the filter 1 and this is arranged to be of the same colour as that of the light transmitted by the filter 1 at the freezing point. In this case the filter will appear black at all temperatures other than at the ice point. Coloured glass may be arranged around the filter 1 to present a distinctive pattern or even wording to the driver of a vehicle under icing conditions. The reflector 2 may be of the kind normally used in vehicle reflectors as shown or may be a convex mirror disposed to reflect a divergent beam back towards the vehicle, or two plane mirrors at right angles giving a horizontal reflected beam. These plane mirrors may also be replaced by convex mirrors if desired.