If they both have a medium base why do they have different base numbers? Bought 40W LED bulbs for my outside door lights for my house. One had a A15 base with lower lumins than the bulbs with a A19 base. They both fit in the outdoor light sockets. If they're both medium base, then they should have the same base number, but they don't. Can I use either one in my outdoor light socket with no problems? Thanks, Ken

The A15 and the A19 number is the designation of the bulb size, not the medium base. Bases or socket numbers begin with "E". The diameter of lamps is measured in 1/18ths of an inch, so the A15 lamp is 1.875 or 1-7/8ths inch diameter, and the A19 lamp is 2.375" or 2-3/8ths inch diameter. This is a carryover from glass manufacturing. Lamps will have several specifications: type of base- E26 is for medium base, shape of bulb, "A" in your case, size of bulb - 15 & 19 in your case, wattage, lumens, and color temperature. Clear as mud?