Response to Hi, CJ. This LED Bulb - PL5815 is NOT compatible with the Amerlite - 78458100 fixture, you will need the 120V 18W - PL5814 or 120V 35W - PL5809. You will also need to replace the Lens Gasket - 79101600 (OEM), PL5851(Generic), LPL-G-P (Heavy Duty). 

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