Characterization of a smartphone camera's response to ultraviolet A radiation

Abstract

As part of a wider study into the use of smartphones as solar ultraviolet radiation monitors, this article characterizes the ultraviolet A (UVA; 320-400 nm) response of a consumer complementary metal oxide semiconductor (CMOS)-based smartphone image sensor in a controlled laboratory environment. The CMOS image sensor in the camera possesses inherent sensitivity to UVA, and despite the attenuation due to the lens and neutral density and wavelength-specific bandpass filters, the measured relative UVA irradiances relative to the incident irradiances range from 0.0065% at 380 nm to 0.0051% at 340 nm. In addition, the sensor demonstrates a predictable response to low-intensity discrete UVA stimuli that can be modelled using the ratio of recorded digital values to the incident UVA irradiance for a given automatic exposure time, and resulting in measurement errors that are typically less than 5%. Our results support the idea that smartphones can be used for scientific monitoring of UVA radiation. A smartphone camera image of an ultraviolet-A (UV-A) beam from an irradiation monochromator. The smartphone camera CMOS sensor can detect the UV-A irradiance, providing measurable responses from the red, green and blue pixels. The addition of neutral density and narrow bandpass filters ensure that the UV irradiance do not cause saturation within the smartphone image sensor.