Method and apparatus for the measurement of rapid light variation superimposed on a slowly changing background light intensity

A device for the measurement of variations in incident light, where the incident light is composed of background light, changing relatively slowly, and rapidly changing light variations, comprising a light sensitive element producing a signal, indicative of the incident light,

• wherein a separate first light emitting element is arranged to emit extra light into said light sensitive element, this first light emitting element being located in such a way that the extra light will pass directly to the surface of the light sensitive element and is not disturbed by any objects in the neighborhood, and
• the amount of said extra light emitted from said first light emitting element is controlled to cause the sum of said extra light and said background light, incident upon said light sensitive element, to be substantially constant.

A process for the measurement of variations in incident light, comprising the steps of:

• deriving the incident light source and wherein said incident light is comprised of background light, which changes relatively slowly, and rapidly changing light variations,
• producing a signal from a light sensitive element indicative of the incident light;
• arranging a first light emitting element to emit extra light into said light sensitive element, the amount of said extra light emitted from said light emitting element being controlled to cause the sum of said extra light and said background light, incident upon said light sensitive element, to correspond to an amount of light, which is located on a substantially linear portion of the characteristic curve of the light sensitive element.

A device for the measurement of variations in incident light, where the incident light is composed of background light, changing relatively slowly, and rapidly changing light variations, comprising a light sensitive element producing a signal, indicative of the incident light,

• wherein a first light emitting element is arranged to emit extra light into said light sensitive element, this first light emitting element being located in such a way that the extra light will pass directly to the surface of the light sensitive element and is not disturbed by any objects in the neighborhood, and
• the amount of said extra light emitted from said first light emitting element is controlled to cause the sum of said extra light and said background light, incident upon said light sensitive element, to correspond to an amount of light, which is located on a substantially linear portion of the characteristic carve of the light sensitive element.