Donnelly Corporation

Edward A Gahan

Kenneth Schofield

Keith W Molyneux

The specification discloses an automatic rearview mirror which more accurately responds to the glare-reduction needs of the vehicle operator. The mirror includes a reflective element, a light sensor, and a control circuit for regulating the reflective state of the mirror in response to the light sensor. The light sensor includes a detector responsive to electromagnetic wavelengths and a filter for filtering the wavelengths received by the detector so that the spectral response of the light sensor approximates the spectral response of the human eye or standard C.I.E. observer. The light sensor therefore detects the same wavelength intensities as does the vehicle operator.

Automatic rearview mirror with filtered light sensors

The specification discloses an automatic rearview mirror control circuit which models the physiological response of the human eye to fluctuating light levels as observed in typical driving conditions. The control circuit calculates an ambient light signal representative of light levels within the driver's field of view and a rear light signal representative of light levels in a direction generally incident to the reflective element. The reflectivity of the reflective element is controlled to optimize rear image information while minimizing on rear image glare at the driver's eyes. The control circuit includes a multiple-rate filter for time-averaging an ambient light signal over a shorter time period during increasing ambient light intensities than during decreasing ambient light intensities to simulate the more rapid adaptation of the human eye to increasing light intensities than to decreasing light intensities. The control circuit automatically alters or adjusts the sensitivity of the mirror to rear light based on the ambient light level. The mirror is more sensitive to rear light in relatively low ambient light, such as experienced on rural highways, than in relatively high ambient light, such as is experienced on urban highways. The control circuit calculates ambient light within the driver' s field of view. The calculation takes into account the forward light, rear light reflected from the interior rearview mirror, and/or rear light reflected from the windshield, pillars, headliner, and exterior rearview mirrors.

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Holland, MI, United States of America

Edward A Gahan