A lux meter works on the principle of photometry by using a photosensitive sensor, typically a photodiode or phototransistor, to convert incident light into an electrical signal, usually a proportional electrical current or voltage.

 A lux meter works on the principle of photometry by using a photosensitive sensor, typically a photodiode or phototransistor, to convert incident light into an electrical signal, usually a proportional electrical current or voltage. This electrical signal is then processed and calibrated to display the illuminance (light intensity) of a surface in units of lux (lumens per square meter), indicating how much light is falling on that specific area.  

Here's a breakdown of the principles:

1. 1. Photometric Sensitivity:

   The core principle is photometry, the science of measuring visible light in a way that accounts for the human eye's varying sensitivity to different wavelengths. 
2. 2. Photoelectric Conversion:

   A photocell (like a silicon photodiode) acts as the light sensor. When photons from light strike this semiconductor material, they create electron-hole pairs, which alters the electrical characteristics of the sensor. 
3. 3. Electrical Signal Generation:

   This change in the sensor's electrical properties generates an electrical current or voltage proportional to the intensity of the light that has hit the sensor. 
4. 4. Signal Processing and Calibration:

   The electrical signal is then processed by internal circuitry. The device is calibrated to convert this electrical output into a measurement of illuminance, displaying the value in lux on its screen. 
5. 5. Illuminance Calculation:

   One lux is equivalent to one lumen of luminous flux falling on one square meter of a surface. Therefore, the lux meter effectively calculates the density of light on the surface it is measuring.