If you have an incandescent lamp determine the wattage of your bulb and write it down. Then, find the bulb to the right which most looks like the bulb you are searching for. Make a note of the letter(s) which identify your bulb's wattage and shape before going forward.
The number behind the letter refers to the diameter of the bulb (or the Eighths Number which we will find in Step 2). The number next to the bulb in these pictures may not be the correct number for your bulb. The letter is what you're interested in finding in this step.
If you do have a fluorescent lamp, go to the next step to find your bulb shape.