The sensor of the testo 540 is similar to the spectral sensitivity of your eye which makes it ideal for measuring actual light intensity. The 540 features a convenient hold function and displays max/min values on a large backlit display. It's a handy, strong and easy to operate little meter. Hold function and maximum/minimum values. Incl. calibration certificate. Protective cap for safe storage. Including wrist strap and belt clip. Sensor comparable to spectral sensitivity of the human eye. Display light. 32 to 122 degree F operating temperature. 2 AAA battery. 200 hours of battery life. Measures 5" length by 1.7" width by 1" height. Probe type Lux. Measuring range 0 to 99.999 Lux. Accuracy: +/- 3 Lux or 3 percent of reading (compared to reference). Resolution: 1 Lux (0 to 19.999 Lux). 10 Lux (remaining range).