3157 VS 4157 Bulbs | What’s The Difference?

In this article, we’ll be taking a look at the major differences between 3157 and 4157 bulbs.

Because of their similar naming schemes and design, these two bulbs are often considered to be interchangeable.

While that is true, there are some subtle differences between the two in terms of performance and longevity.

The biggest difference between these two bulbs is lifespan.

Specifically, 4157 bulbs are a newer design that is longer lasting than its 3157 counterparts. Furthermore, 4157 bulbs feature nominally higher brightness output.

Having tested the vast majority of options for both types of bulbs, we can help you make a more informed decision about which one to buy.

Keep reading for more info on the differences between 3157 and 4157 bulbs.

Lifespan of this bulb is shorter Newer, longer lasting bulb design
Does not have Krypton gas in the bulbUses Krypton gas in the bulb
Dimmer bulbSlightly brighter light output
Rated for 27 wattsRated for 29 watts
3157 VS 4157 Bulbs

3157 and 4157 Bulbs Compared

Power rating

There is a slight difference between 3157 and 4157 bulbs when it comes to the power rating and wattage. 3157 bulbs are rated for 27 watts whereas 4157 bulbs are rated for a slightly higher 29 watts.

Day to day, we did not notice the biggest difference in terms of light output or visibility. However, 4157 bulbs do offer a bit more clarity when viewed up close.

Gases used in the bulb

Being a new design of bulb, 4157 bulbs utilize Krypton gas in the bulb which allows for better, more clear light output, and extended lifespan when compared to 3157 bulbs which do not have Krypton gas in the bulb.


Our testing concluded that the difference in brightness between these two bulbs is not that noticeable in the real world. However, there is a difference on paper. 4157 bulbs are rated to produce a couple more lumens than 3157 bulbs.

However, we would like to reiterate that the difference in brightness alone should not influence your buying decision when it comes to these bulbs.


The most noticeable difference, and one that should definitely be under consideration when trying to choose between these two bulbs, are their lifespans.

3157 bulbs are an older design of bulb and do not last as long as 4157 bulbs.

4157 bulbs utilise better materials, which are more resistant to heat and Krypton gas in the bulb which increases bulb longevity.

In fact, 4157 bulbs are rated to last over four times as long as 3157 bulbs.


We tested a number of different options for both 3157 and 4157 bulbs and found them all to be interchangeable. They have the same exact bulb base, albeit made of slightly different materials, and the connectors are shaped the same as well.

As for the slight difference in power rating, you don’t have to worry about blowing a fuse or getting decreased performance if you swap bulbs. The wattage of both bulbs is within allowable tolerances and will not cause any problems.

3157 Bulb Specs

3157 bulbs rank among the most commonly used sizes for turn signal and brake light purposes. Their single filament design is complemented by a unique socket design, facilitating dual functionality – brake/turn and tail light – within a single bulb.

These bulbs are equipped with a W2.5×16q cap, which typically houses two filaments catering to both low and high beam functions. However, dual filament lamps are not utilized for turn signals or brake lights due to their varying light output levels. Notably, the light produced by the brake/turn and tail functions carries an amber hue, while the headlights emit white light.

The bulb’s nominal power specification, 12 V: 27 / 7 W, represents a single-filament 27-watt bulb drawing 7 watts in a 12-volt system. This power specification positions the 3157 bulb as a dual-function – brake/turn and tail light – bulb.

Cars equipped with these bulbs generally have separate filaments for each function. The brighter 27-watt filament is utilized for brake and turn signals, while the tail lights use the 7-watt filament.

Advantages of this lamp include:

  • Its versatility, enabling it to serve as turn signals, brake lights, and tail lights.
  • Its exceptional brightness, making it ideal for turn signal or brake light applications.
  • Its socket design that allows for dual functionality – brake/turn and tail light – within a single bulb.

On the downside:

  • The bulb lacks clear or smoked lens variants, rendering it unfit for backup light applications.
  • The 3157 bulb is not legal in all states. Some jurisdictions require separate bulbs for turn signals and brake lights.

4157 Bulb Specs

4157 bulbs not only boast a longer lifespan compared to standard lightbulbs but also exhibit superior durability against wear and tear. They serve as the perfect choice for both interior and exterior illumination needs of your vehicle.

The 4157 lamp possesses a W2 5x16d base, operates at a voltage of 12V, and utilizes 28.54W of power. This level of nominal power characterizes the bulb as dual-functional, serving both as a turn signal and brake light. The 4157 model measures 2.5 inches in width and 16mm in length.

The design includes two filaments, dedicated to low and high beam functionality. The light produced by the brake/turn and tail functions exhibits an amber hue, while the headlights emit a white light.

Benefits of employing this lamp include:

  • Its color temperature closely mirrors natural sunlight, offering a soothing visual experience.
  • Its impressive lifespan signifies a smart and durable investment.
  • Its versatile usage covers turn signals, brake lights, as well as tail lights.

However, there are a couple of potential downsides to consider:

  • The emitted light is notably bright, which may not be ideal if a subtler illumination effect is desired.
  • The 4157 model doesn’t come with clear or smoked lens options, limiting its utility as a backup light.


So, to sum up, 3157 and 4157 bulbs are quite similar and only differ in a few ways.

After testing most of the options for each bulb, we have concluded that of the two, 4157 bulbs are the superior choice. No matter how small, there is a difference in brightness and power of the bulb.

But what really seals the deal is the difference in longevity. 4157 bulbs feature a four times longer lifespan, compared to 3157 bulbs. That means you will have to replace bulbs less often, while still enjoying as good as, if not better performance than with 3157 bulbs. All said and done, 4157 bulbs offer the best bang for your buck.

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Hi, I'm Graeme, the author and owner of HeadlightReviews.com. Before I started this hobby site, I used to work alongside my 'Pops', helping out as he worked as a mechanic for over 50 years. Twenty-five of those he was running his own Auto Electrician & Body Shop, where I fell in love with vehicle lighting. I've taken all our experience online (that's not his gig)… so it’s safe to say there are very few people on the internet who can match our expertise and deep understanding of vehicle mechanics, repairs, parts, and especially headlights. If you've got a bulb question, contact me here, and read more about me and headlightreviews.com here.

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