Lightbulbs are hella confusing. LED-A19-E26. What in the world does that mean?! I don't speak that language!
Luckily it actually isn't tooooo bad. I'm going to throw together a few charts, tips, and tricks, and pretty soon you will be speaking lightbulbs like a pro :)
First, lets talk about the bulb shape. This is denoted by a letter and a number. Generally the letter refers to the bulb shape (A for arbitrary, C for candle, G for globe and so on).
Pretty simple, right? The majority of the lights I make for Rough Luck Studio are able to incorporate a variety of bulb shapes. When I photograph a fixture that the bulb is exposed I'll usually use a G25, just for consistency. A lot of the fixtures look great with different shaped bulbs. I love the look in this client photo that features a double-Lillian sconce with T10 bulbs.
Play around with it! Changing the bulb shape is a great way to alter the architectural look of a fixture and also to modify the texture and quality of the light that it'll throw. As Miss Frizzle once said, "Take chances, make mistages, get messy!"