I have an electrical related to my pool lights. I have a pentair spa light that bulb needs to be changed. It is a 100W fixture, R20 medium base bulb. I would like to replace it with a colored bulb. I found a few R20 colored bulbs but all are about 2 cm longer than the bulb in there and don't fit. I would have thought all R20 bulbs would be the same size. Since I can't fins an appropriate size R20 could I put in a different bulb say a PAR20 medium base bulb equal to or less than 100W? Does the shape of the bulb matter or type of bulb?