Cutoff Line - Crucial Assurance For Nighttime Driving
As night descends, the roads plunge into utter darkness, and the headlights of cars become the driver's best companions. Have you ever wondered why the headlights of some cars project a clear horizontal line onto the ground?
Therefore, let's explore what cutoff line is, its functions, and delve into related Q&A. Understanding this blog will not only help you upgrade to LED headlights but also enhance road safety by reducing glare. Join us in exploring the world of cutoff lines.

What is the cutoff line?

Cutoff line, refers to the edge of the light beam projected onto the road by a vehicle's front headlights, typically appearing as a clear horizontal line. Above this line is the bright area, while below is a relatively darker region. The existence of the cutoff line aims to reduce the glare effect of a vehicle's headlights on the driver of oncoming vehicles. The cutoff line often takes a "Z" shape, effectively directing the light beam onto the road, preventing upward scattering, and minimizing interference with oncoming drivers. This design contributes to enhancing nighttime driving safety and reducing the risk of accidents caused by headlight glare. The presence of the cutoff line is primarily achieved through the design of lenses and reflectors. Some vehicles employ specially designed lenses to control the direction of the light beam based on their shapes. Reflectors help prevent light from scattering upward. This design not only assists drivers in clearer visibility of obstacles on the road but also improves the comfort and visibility of nighttime driving.


Cutoff Line plays a crucial role in the design of a vehicle's front headlights, primarily by guiding and controlling the direction and range of light projection to enhance nighttime driving safety. The following are the key functions of the cutoff line:
  • Reducing Glare: It effectively reduces the glare effect on oncoming drivers and pedestrians. By forming a distinct horizontal line, it prevents the upward scattering of light, minimizing interference with other road users, especially during nighttime or adverse weather conditions.
  • Improving Visibility: The cutoff line contributes to ensuring that the light beam is concentrated on the road, enhancing the driver's visibility of road obstacles. By creating a clear boundary line, it makes it easier for drivers to discern changes and obstacles on the road.

The presence of the cutoff line not only minimizes glare for oncoming traffic but also optimizes the illumination pattern, contributing to a safer and more comfortable driving experience in low-light conditions.

Products Recommended

 1. COLIGHT Y12 Series

Y12 series featured with a perfect cutoff low beam and mini size.
It replace the front reflector housing headlight or fog light. Small size as halogen, won't affect the installation of the dust cover.

  • Tips:
  • Can be only used in Left-Hand-Drive country
  • H4 Bulb: Low beam 60W/6000LM; High beam 80W/8000LM
  • H7/H11/9005/9006 Single beam 60W/6000LM
 2. COLIGHT 7inch J013 Series

Boasting DOT certification and adherence to road traffic regulations, J013 series headlights not only provide a flawless Z-shaped cutoff line that won't blind drivers ahead but also feature yellow and white daytime running lights, adding a touch of personality to your vehicle.
The Z-shaped low-beam cutoff line ensures a clear boundary when the headlights illuminate forward, preventing excessive scattering of light. At the same time, it provides sufficient brightness to ensure the safety of nighttime driving.
Please check product details for applicable car models:

 3. COLIGHT 4x6inch T001 Series

With perfect cutoff low beam and yellow-white DRL, this 4x6 sealed beam T001 series headlight not only provides a brighter lighting effect and wider field of view, but also adds a personalized appearance to the vehicle. Specially provided for classic car enthusiasts, comes with the H4 adapter plugs for plug-and-play. DOT SAE compliant, legal for all 4x6 systems with 12V and 24V compatible.
Beam pattern: high beam(54W/6000 lumens) /low beam(60W/6600 lumens), white DRL, yellow DRL.
Please check product details for applicable car models:


Throughout this blog, we have explored what a cutoff line is, its functions, and the profound impact it has on the safety of nighttime driving. Remember, a clear cutoff line is not just for better illumination but also serves to protect both yourself and others on the road, playing a crucial role in every nighttime journey.
Cutoff line has played a significant role in improving the driving experience and reducing the risk of accidents. We hope that everyone can drive safely at night, recognizing the importance of this critical element in automotive lighting.


1. What are the types of cutoff line shapes?
The shape of the cutoff line can be horizontal, sloping, etc., depending on the design choices of the vehicle manufacturer. Some models adopt special designs such as a Z-shaped or other geometric shapes to optimize lighting effects.
2. Why is the cutoff line in a "Z" shape?
The cutoff line takes a "Z" shape as the light is focused through the reflector cup, directed to the shading plate, and then projected through the lens. This configuration, resembling two lines on a horizontal plane, ensures that it does not obstruct the line of sight of oncoming drivers, while maintaining a normal illumination distance for our side.
3. Why is cutoff line important?
The presence of the cutoff line helps reduce glare during nighttime driving. By confining the light beam to a specific area, the illumination becomes more focused and organized, preventing visual interference for oncoming drivers.
4. How is the cutoff line implemented?
The implementation of the cutoff line is typically achieved through the design of optical components in the vehicle's front headlights, such as lenses and reflectors. These components guide and restrict the light beam in the horizontal direction, forming a clear cutoff line.
5. Is the cutoff line adjustable?
Some vehicle models utilize an automatic adjustment system to alter the position of the cutoff line based on factors such as speed, load, and driving conditions. This helps adapt to different driving scenarios, providing optimal lighting effects.