What is the Difference Between E39 and EX39?

When we enter the realm of lighting fixtures, it’s common to stumble across jargons and codes that might seem like cryptic puzzles. It’s especially true when examining bulb bases and socket sizes. The difference between E39 and EX39 may sound subtle, but it holds significance in the realm of commercial lighting. These designations relate to the base design and dimensions of certain light bulbs, and understanding them can be crucial to ensuring you choose the right product.

E39 E40 Mogul Edison Screw Ceramic Lamp Holder Socket with Mounting Bracket

As a part of James Lighting, I’ve encountered numerous scenarios where this knowledge made all the difference in product selection. Let’s delve deeper into this topic.

What are E39 and EX39 Anyway?

E39 is commonly referred to as the “mogul” base, primarily used in North America. These bases have a diameter of approximately 39 millimeters. On the other hand, EX39 denotes an extended mogul base.

While both bases serve similar functions, their distinctions lie in their design and application. And trust me, once we’ve sifted through these nuances, you’ll appreciate the depth of detail that goes into lighting design.

How Does the Design Differ?

E39, being a mogul base, is standard in design. It provides a secure connection to the socket. In contrast, the EX39 is an extended version, with the threads of the base positioned slightly higher than the E39.


This extension is not merely for aesthetic appeal. It serves a purpose, particularly when it comes to accommodating certain types of lighting fixtures. When I show clients samples at James Lighting, they often marvel at the thoughtfulness behind such design alterations.

What’s the Purpose of the Extension in EX39?

The extension in EX39 ensures that the base of the bulb does not interfere with certain components of the lamp, particularly in HID fixtures where the ballast or other elements might be in proximity.

Having been involved in countless installations, I’ve witnessed firsthand how this small design tweak can make installation smoother and safer. It’s an insight into how minor changes can substantially influence functionality.

Can I Use E39 and EX39 Interchangeably?

Technically, both E39 and EX39 bulbs can fit into the same mogul socket. However, the EX39 is specifically designed to accommodate fixtures where additional space is required above the socket.


From my experience, it’s essential to be cautious. If a fixture recommends an EX39 bulb, it’s best to adhere to that recommendation. At James Lighting, we always emphasize the importance of compatibility to ensure the longevity and safety of our products.

E39 6KV porcelain light socket ceramic lamp holder UL

How Do I Identify the Right Base?

A simple rule of thumb is to check the fixture’s recommendation. However, it’s also possible to measure the base’s diameter and height to ascertain its type.

Over the years, I’ve often advised our clients to either bring a sample or share detailed specifications. It ensures that when they walk out of James Lighting, they carry the exact product they need.

Are There Specific Applications for Each Base?

Both bases cater to high-wattage lamps often found in commercial and industrial settings. While E39 bases are more generic, EX39 bases cater to specific fixtures where the extended design is necessary.

E39 4KV porcelain light socket ceramic lamp holder UL

It’s like fitting a puzzle piece – every design has its place. As we assist clients in their lighting journey, understanding these applications ensures they get optimal performance from their fixtures.

Why Does This Distinction Matter?

In the grand scheme of things, knowing the difference between E39 and EX39 might seem trivial. However, when dealing with high-wattage systems, every detail matters for safety and efficiency.

At James Lighting, our emphasis has always been on guiding clients to make informed decisions. Knowledge about these bases helps prevent potential malfunctions and ensures the durability of the lighting system.


In conclusion, the world of lighting is brimming with intricate details. The distinction between E39 and EX39 serves as a testament to the industry’s dedication to precision and innovation. Whether you’re a lighting enthusiast or a professional seeking to understand the intricacies, remember that at James Lighting, we’re here to illuminate your path.

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