If you are seeing it across a lot of the matrix, that is not likely just one or two simple causes such as a failed LED. In some cases, using anti-ghosting design LEDs can alleviate the problem...but not always. For WPC based games, there are some specific "fixes" you might look into. Some info here: http://www.edcheung.com/album/album07/Pinball/WPC_Ghost_Busting.pdf

I'm not well versed in WPC ghosting but I can tell you ghosting problems can vary from game to game, and can vary depending on the LEDs used. My Williams System 11 Taxi ghosted terribly on almost all lamps with standard CTs, the only fix for me was to remove them - while on other games I didn't have the problem. F-14 Tomcat worked flawlessly with the CT premiums. Just my personal observations.

For really obnoxious locales, another option is to try using a bulb cap over the LED to cut intensity down.

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