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Summary:A required visual signal for direct observation is produced from a first source of light (4) in the presence of a second source of light, such as ambient light. Light is transmitted from the first source to a defined surface (10) or defined region distant from the first source (4). A means (10) for modulating light is operated between at least a first mode and a second mode. This operation is synchronised with a varying of the intensity of at least one of the sources of light at or above a given frequency equal to or greater than the critical fusion frequency for the size and luminance of the required visual signal. When the modulating means (10) is in the first mode, this allows the required visual signal to be directly observed on the defined surface or in the defined region. When the modulating means (10) is in the second mode, this allows the effect produced by any light from the second source incident on the defined surface or in the defined region to be reduced.
Bibliography:Application Number: AT19890310225T