I need to change the bulb on my spa light. It is a pentair light and calls for an r20 bulb. I would like to put in a colored bulb but the three that I have bought are all a centimeter or two longer than the one in there. I would have thought all r20 bulbs were a standard length?? The r20 is a medium width base bulb. Can I take say a different medium width base bulb, say a PAR20, of the the same or lower watts and came volts and replace it with that?