OPT4001/OPT4001-Q1 Digital Ambient Light Sensor Texas Instruments OPT4001/OPT4001-Q1 Digital Ambient Light Sensor (ALS) is a light-to-digital sensor that measures the intensity of visible light. The sensor's spectral response tightly matches the human eye's photopic response. A specially engineered filter on the device rejects near-infrared components from the common light sources to measure accurate light intensity.