Often, when it is time to replace a light bulb the easiest course of action to take is to look at the bulb that you take out and simply replace it. What if you want to understand what you have so you know how to search for a replacement? The numbers and letters are abbreviations and with the knowledge of what they mean you can easily look for the light bulb you want.

Wattage:

Wattage is the amount of energy the light uses per hour. In the same family of light bulbs (like incandescents) the higher the wattage the brighter the light is. The disadvantage is that you use more energy. So, if a light bulb is 100 watts, you are using 100 watts of energy per hour. You'll often see this shortened and will see the abbreviation look like this: 100W or 100w. If you are using a compact fluorescent the number will be more like 16w.

Bulb Shape:

With Philips Lighting, for example, there are at least 50 bulb shapes in incandescent light bulbs. With halogen and halogena' you will find at least 32 bulb shapes. In Philips Fluorescent and Compact Fluorescent groups there are at least 38 bulb shapes. And lastly with HID, Specialty and LED light Bulbs there are over 50 bulb shapes.

If you are using a PAR38 in your recessed lighting, that same bulb shape is available in an incandescent, halogen, compact fluorescent or metal halide. The overall length may vary a little but the basic shape of the light bulb will be the same.

How do you know what bulb shape you have? The letters used aren’t really abbreviations. Examples of bulb shapes: BT15, BR40, PAR38, T4, G25, A19 and so on. A19 is your common incandescent light bulb often used in table lamps. F, B & BA Shapes are used generally in chandeliers and sconces. BR, ER, PAR, R and others are used in recessed lighting and some outdoor lighting. G are globe light bulbs commonly used in vanity lighting. This is not all the shapes but you get the idea.

If you live in California, you might be surprised to know that the state requires contractors of new construction to insert certain fixtures that only use compact fluorescents. These will often take PL bulbs shapes. They are PL-H, PL-S, PL-C, PL-L and PL-T. They vary in regards to base style and length and number of tubes you see on the bulb.

Base Type:

The most common base types are Medium base and Candelabra base. Medium base is the regular size that is roughly 1" in diameter. Candelabra base is the much smaller base that is used mainly in sconces, chandeliers and some small portable lamps.

In California the base types of the plug in light bulbs are written like this: G24d-3, G23, 2G8-1, G24q-1 or something in a similar sequence.

Voltage:

Voltage should be chosen based on the voltage of power that is coming into your home. This is indicated in either 120V or 130V. If you have put a 120V light bulb in a table lamp and you’ve blown a couple pretty quickly, you most likely need a 130V light bulb.

Low voltage lighting is 12 volts or 12v and is generally halogen light bulbs.

Spot Vs Flood:

Spot or a flood often used in recessed cans each have varying degrees of swath of light. It might be 10(degrees), 25, 32 or 40 or any number around this range. Spots are a narrower beam and flood light bulbs have a larger beam of light.

Color:

Sometimes you will see on your bulb a number like 827, 830, 835 or 841. All of these numbers are the different colors that Philips compact fluorescent plug ins come in. Other light bulbs may come in varying colors as well.

By grasping these simple indicators, most will be able to figure out what kind of light bulb they are holding. Good luck to you.