How long have you been using it ? .... the electroluminescent film does deteriorate over time and will eventually dim out and cease to work.
My local hobby shop had one on display, operating 12 hours a day for about a year and a half before it finally died out.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ