This part is a kind of semiconductor called GL5549.
Function of this product has (GL5516 - GL5659D) PHOTO CONDUCTIVE CELL.
Manufacturers : ETC
Image and pinout :
Some of the text within the PDF file :
PHOTO CONDUCTIVE CELL Features ■ Epoxy Encapsulated ■ Smali Size ■ Quick Response ■ Reliable Performance ■ High Sensitivity ■ Good Characteristic of Spectrum Applications ■ Auto Flash For Cameras ■ Room Light Control ■ Photolamp ■ Industrial control ■ Photoelectric Control ■ Annunciator ■ Photoswitch ■ Electronic Toys Measuring Conditions 1. Light resistance: Measured at 10 Lux with standard light A (2854k color temperature) and 2 hours illumination at 400-600 lux prior testing. 2. Dark Resistance: Measured 10 seconds after closed 10 lux. 3. Gamma Characteristic: The relation betweem the rate of change of resistance and the variation of incident ray may be calculated through the formula noted below: R10.R100 Cell resistance at 10 lux and 100 lux,The error of is [ ... ]