- on Test & Measurement
- Published in issue 7/2004 on page 0
Light Sensor Technology
measuring daylight using LEDs
Light-sensitive sensors with characteristics similar to those of the human eye are most often implemented using photoresistors or special (and thus expensive) photosensors. Few people realise that normal LEDs can also be used as optical sensors that respond the same as the human eye.Photodetectors for visible light are most often built using light-dependent resistors (LDRs), which are well-known components. Their spectral sensitivity is similar to that of the human eye. In the SMD age, their ‘pros and cons’ are their large package sizes, large tolerances, large temperature dependence and large sensor currents, besides which they are expensive and very slow. The speed at which LDRs respond to varying light levels is similar to that of the human eye, with resistance changes occurring in the range of seconds.