The Ultimate Guide to Light Bulbs

Last Updated

While light bulbs seem like a simple product, they can be more complicated than you think. What’s a PAR? What is the difference between PAR and MR? In this article we’ll look at everything you could ever need to know about light bulbs so you’re not left in the dark.  

Light bulb codes are made up of letters and numbers. The letters refer to the shape of the bulb, where the numbers refer to the base type. However, helpfully, light bulb base types also include letters, so these will need to be read separately.

Light Bulb Shape Codes



Arbitrary/Standard household GLS (General Lamp Service)
B Blunt/Bullet Often used interchangeably with C
BR Bulged reflector Often used interchangeably with R
C Candle/Conical
G Globe Golf Ball
T Tube/Tubular
R Reflector
PAR Parabolic Aluminized Reflectors
MR Multifaceted Reflector


Light Bulb Base Codes

The letter in light bulb base codes refers to the type of base, whereas the number typically refer to the size of the base itself. For example E10 is a 10mm screw base, whereas an E11 is an 11mm screw base. For this reason, there are a lot of base codes, so we’ll just look at the most popular bases we sell here at LED Bulbs.

Screw base

Screw bases will generally start with an E as they are technically called Edison base bulbs.

 E27 Base E14 Base
E27 E14



Bayonet bases are easier, called B for Bayonet.

 B22 Base B15 Base
B22 B15



Spotlights will typically use GU bases, which stands for General Use. GU5.3 bulbs are often called MR16, but the MR refers to the bulb shape, not the base.

 GU10 GU4 GU5.3
GU10 GU4 GU5.3