Originally Posted by AthenaHolloway

Thanks for sharing it with us, I appreciate you for taking the time to write it.

Originally Posted by lasfit

The 3157 and 3156 are two widely used bulbs for turn signals, brake lights, and taillights. Have you ever learned about these two types of lights when you were picking out LED turn signals for your vehicle? Is there still some confusion about the difference between these two? Are you not sure how to pick the right bulb? This article will introduce you to 3157 and 3156 and hopefully help you out!

What's The Difference Between 3157 And 3156?
The main difference between 3156 and 3157 bulbs lies in the number of filaments. The 3156 bulb has only one filament, while the 3157 bulb has two filaments.

To determine whether it is LED 3157 or LED 3156, the main difference lies in the wiring. The 3156 bulb has only one wire, while the 3157 bulb has two wires.

Installation Position
As for the installation position, due to the dual filaments of the LED 3157 bulb, it has both high and low brightness, making it a dual-function bulb. When used as a front turn signal, the 3157 bulb can simultaneously function as a turn signal and daytime running light (DRL). When you activate the front turn signal, the high brightness of the bulb serves as the turn signal. In contrast, low brightness is usually used for DRL or parking lights. Additionally, the 3157 bulbs can also be used as side marker lights on some trucks.
When installed in the rear lights, the 3157 bulb is typically used as a tail light and brake light. Some American trucks, like F-150 trucks, may have a combination of tail, brake, and rear turn signal functions using a single 3157 bulb.
On the other hand, the LED 3156 bulb has only one filament, making it a single-function bulb. It has only one brightness level and cannot switch between high and low brightness like the 3157 bulb. It cannot be used simultaneously as a turn signal and DRL.
Due to its attributes, the 3156 bulb is primarily used for front or rear turn signals, reverse lights, and parking lights.
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Are 3157 And 3156 Interchangeable?
When replacing or upgrading the lighting system, ensuring compatibility between the existing socket, wiring, and bulb is crucial.
The base of the 3157 and 3156 bulbs is the same, so the 3157 bulb can be installed in the base of a 3156 bulb, and vice versa. But will they work?
When a 3157 bulb is installed in a 3156 socket, it can still illuminate. One of the two filaments in the 3157 bulb will receive power and light up, allowing it to function similarly to a single-filament 3156 bulb.
On the other hand, if a 3156 bulb is installed in a 3157 socket, it will only produce a fixed level of brightness. The reason is the 3156 bulb is intended for single-filament operation, whereas the 3157 socket is designed for dual-filament bulbs. The different wiring of the two prevents the 3156 bulb from functioning in the same manner as the 3157 bulb within a socket specifically designed for dual-filament bulbs.

How To Pick The Correct LED Bulb?
How do you pick the correct LED bulb model? It depends on the size of your factory halogen bulbs. Here are some tips to assist you in choosing the appropriate LED bulb.
1. Review the user manual
You can consult your vehicle's user manual, which typically provides details about the bulb size of the factory halogen bulbs. Once you have determined the bulb size, you can purchase the corresponding LED bulb based on the information in the manual.
2. Inspect the factory halogen lights
You can remove the factory halogen bulb that requires replacement. Usually, the halogen bulb socket will show the corresponding model number. By identifying the model number, you can purchase an LED light with the same model to ensure compatibility.
However, this method is a bit more cumbersome, some vehicles are not convenient to take out the halogen bulb. additionally, individuals with limited experience in bulb modification might be hesitant to undertake this task, fearing potential damage.
3. Search on the Lasfit website
Another useful resource is the Lasfit website, where you can search for the correct LED bulb model specific to your vehicle's make, model, and year. Our website provides detailed categorization, making it easier for you to locate the appropriate LED bulb. Here is the link for you: LASFIT

Conclusion
The difference between 3157 and 3156 is mainly in the number of filaments.
When choosing between LED 3157 and LED 3156 bulbs, it depends on the factory bulb size of your vehicle.
When a 3157 LED bulb is installed in a 3156 socket, the light will function normally. However, if a 3156 LED bulb is installed in a 3157 socket, only one function will work as the 3156 bulb is a single filament bulb.
Lasfit's upgraded T3 series only offers one model, T3-3157, which is compatible with both 3156 and 3157 bulbs. So, whether your vehicle's bulb size is 3156 or 3157 bulbs, you can purchase our T3-3157. However, please pay attention to the color choice - whether you need red or amber.
Have you ever installed LED 3156 or 3157 for your turn signals? Feel free to share your experience with us in the comments!