The HOBO Light On/Off data logger monitors indoor light changes with an internal sensor and records light on and off conditions, making it ideal for building energy audits and light usage analysis. The HOBO UX90-002 Light On/Off Data Logger is available in a standard 128 KB memory model (UX90-002) capable of 84,650 measurements and an expanded 512KB memory version (UX90-002M) capable of over 346,795 measurements.