GU10 vs MR16 bulbs

GU10 and MR16 light bulbs
GE10 light bulb with round feet and MR16 with prongs


In this post I answer the question of what are GU10 vs MR16 light bulbs.

GU10 is a connector

Lets start with what GU10 is not. It is not a definition of the light bulb. Rather it defines the connector at the bottom of the bulb. GU stands for General Usage and the 10 is the distance between the connectors. That is 10mm or 0.04 inches.

MR16 is a bulb shape

On the other hand MR16 is a descriptor of the bulb type. MR stands for multifaceted reflector with a maximum diameter of 16/8th of an inch. So 2 inches or 5cms. Also, MR16 bulbs use a 2-prong connectors, called a GU5.3.

They run on different voltages.

So far so relatively straight forward. To confuse things more MR16 bulbs run on 12 volts. As we have 120 volts here in the United States they need to have a step-down transformer in the fixture. In brief a step-down transformer changes the voltage downwards. In this case from 120 to 12 volts.

Additionally both bulbs (even though GU10 is not a bulb) are used in the same fixtures. Namely track lighting and recessed ceiling lighting.

Add to this the fact that the light bulbs used with GU10 connectors are actually MR16 shaped. And that MR16 normally defines a bulb that runs on 12 volts. End product a whole heap of confusion.

For example I have seen packaging that says an MR16 light bulb with a GU10 connector. Which is sort of correct but also confusing. Let me explain how the issue came about.

So how did the problem occur?

Effectively both type of light bulbs are MR16 shaped bulbs. And both have GU connectors. What happened is people started calling the ones with the smaller pin connectors MR16. While calling the ones with GU10 connectors GU10.

So really we have one bulb type and two different connectors:

  • MR16 type bulbs with GU10 connectors. These run on 120 volts.
  • MR16 type bulbs with GU5.3 connectors. Running on 12 volts.

Do I need a GU10 or MR16 light bulb?

So, to check if you need a GU10 vs a MR16 light bulb.

  1. Look at the connectors on the old bulb
    • If they are little t-shaped circles then you need a GU10 bulb
    • If they are straight pins you need a MR16
  2. Check the power requirements
    • GU10 bulbs use 120volts
    • MR16 bulbs use 12volts

In conclusion

Hopefully this has gone some way to explaining how GU10 vs MR16 light bulbs differ. If you are interested in buying these bulbs why not check out our best of articles here.

Also both types of bulbs are readily available at Amazon and big-box stores such as Home Depot and Lowes.

The video below gives details on changing either of these bulbs.