Before you take a walk down the bulb aisle of a home improvement store, let us help you navigate the choices. There are common terms and descriptions for bulb shapes, base types, and light sources to help ensure you buy the right bulb for the job.
Selecting a light source is an excellent place to start. What source is the bulb you are replacing or if your search is to outfit a new fixture, does the manufacturer give you a recommendation? Most likely you will be reaching for LED, and here’s why…
The light source familiar to many people is incandescent; it’s also the least efficient and limited in the bulb “shapes” and “bases” that are available. Since incandescent works or lights up by electricity running through a filament, it creates a lot of heat and uses a lot of wattages (electricity). They also don’t last very long due to the stress of heating and cooling the metal filament inside the glass. Thus, the U.S. government has moved to minimize the bulb shapes and bases that are available as incandescent.
The twist, spiral or ice cream cone bulb – whatever you call it – remains, but its popularity has waned. This light source illuminates by exciting mercury vapor with an electrical charge that in turn makes a phosphor coating inside the tube (long or twisted) glow. Fluorescent bulbs are modestly priced and use less than half the wattage of incandescent to create the same light output, but the look of the bulb and the fact that they contain mercury, has made them an undesirable option for many people.
There’s a lot to like about LED. As a light source it uses semiconductors (materials that conduct electricity) to produce electroluminescence. Say what? We are talking photons, atoms, and electrons here. The important part is that LED uses a lot less electricity than incandescent, up to 80% less and last a lot longer. A quality LED bulb can last up to 15 years, and that’s a small investment worth making. Bulb manufacturers are also now producing most bulb shapes in LED so finding what you need or want is pretty easy.
Here's a comparison of how the different light sources stack up
The shape of bulb you select is determined either by a constraint of the fixture it is going into or how it looks. Will it “look right” with the style of the fixture.
The six most common bulb shapes and their names are
A (Arbitrary) – the bulb shape most people are familiar with
Candle – shaped like the illuminated aura around the flame when you burn a candle. This shape is also available with a twist or flourishes at the top.
Globe - A sphere-shaped bulb offered in multiple base sizes depending on fixture needs.
Par – resembling a cone, these bulbs are used for directional illumination such as for track, flood or landscape lighting.
CFL, Twist or Spiral - developed to create a shorter overall length alternative to 120V screw base incandescent.
T - Tube bulbs are longer than they are wide and come in a variety of bases. T8 or T12 bulbs fall in this category and usually have a medium bi-pin base to fit into shop lights, clouds or troffer type of fixtures.
The bulb base you need to buy is entirely dictated by what the socket of the fixture accepts and should be noted on the fixture box or the socket. And, gulp; there are hundreds of different types. We are only sharing the most popular ones here. Most bulb bases are named primarily with a letter followed by a number that describes a physical attribute of the bulb, and the most common ones have “nicknames” which also helps. You’ll see what we mean here:
- E stands for Edison, and the number is the diameter of the base measured in millimeters. The base is threaded and screws into the socket.
- E12 or sometimes called chandelier, candelabra or c type
- E17 or often called appliance bulbs
- E26 or medium based, this is the most common bulb base type
- G bulbs were initiated by the U.S. EPA and Lighting Research Center in 2004 for the introduction of CFL bulbs. The number in this bulb description refers to the distance between the pins measured in millimeters. There are over 75 types of G bulbs, but the GU10 and GU24 are the most common ones and are used primarily by hotels. To install you push the pins of the base into the socket and twist to lock in place.
- B (all #’s) or bayonet bulbs are the bulb base found most commonly in the U.K. To install you push it into the socket and twist. They are also sometimes used for automotive bulbs in the U.S. The number associated with a B bulb refers to the diameter of the base in millimeters.
Most importantly when it comes to bulb bases always use the base type noted by the manufacturer for the fixture. This recommendation is what the fixture was designed to accept, safety tested with, looks best, and appropriately fits within all the components of the fixture.
General Need to Know Bulb Facts
All bulbs sold in the U.S. are required to include "Bulb Facts" on the label to inform consumers of exactly what they are purchasing and the results they can expect. These facts include:
- Light output in Lumens
- Lumens per Watt or Efficacy
- Color Accuracy or Color Rendering Index (CRI)
- The Light Color or Correlated Color Temperature (CCT)
- CCT is measured in degrees Kelvin