The diameter of a traffic signal head is chosen by the road class, viewing distance and the type of approach. Compare 200mm (8 inch), 300mm (12 inch) and 400mm (16 inch) LED traffic lights before you commit to a specification.
Size comparison table
| Diameter | Inch equivalent | Typical road class | Visibility distance | Driver decision point | Power per lamp |
|---|---|---|---|---|---|
| 100 mm | 4 inch | Pedestrian, indoor or cycle-path applications: confirm the required indication and approved layout | <50 m | Optional | 3-6 W |
| 200 mm | 8 inch | Side-road, parking or lower-speed urban applications: confirm local design approval | 50-100 m | <60 m | 6-10 W |
| 300 mm | 12 inch | Urban arterial, school zone, intersection | 100-200 m | 60-120 m | 8-15 W |
| 400 mm | 16 inch | Highway, high-speed arterial, fog-prone | 200-300 m+ | 120-200 m | 12-20 W |
1. Why signal head diameter matters
A signal head that is too small is missed at distance. A signal head that is too large is heavy, expensive and hard to mount. The correct diameter matches the legibility distance to the road speed and the approach geometry.
Approach speed, viewing distance, ambient light and background conditions all affect signal selection. Confirm the diameter and optical requirements in the applicable road-authority specification. Product standards and installation rules serve different purposes; a reference to EN12368 or MUTCD does not by itself establish one universal diameter or speed threshold. For projects spanning jurisdictions, obtain acceptance for each proposed configuration rather than choosing solely by size.
2. 200mm / 8 inch: assess pedestrian and lower-speed applications
A 200mm (8 inch) head may be considered for pedestrian, bicycle, parking or lower-speed vehicle applications where the applicable rules permit it. Confirm the required viewing distance, approach conditions, optical performance and mounting arrangement. Diameter alone does not establish a comfortable viewing range or an approved speed band.
A 200mm head may suit a compact or replacement installation when permitted by the approved project requirements. Verify the required indication, viewing conditions, mounting geometry and optical evidence for the chosen model. Check visor and backplate compatibility separately; accessories for one 200mm or 300mm housing need not fit another. Do not assume that a longer arm compensates for a smaller signal face.
3. 300mm / 12 inch: standard urban intersections
A 300mm (12 inch) signal is an option for urban vehicle approaches, but diameter alone does not establish visibility or suitability. Check the approved layout, approach speed, viewing distance, optical performance and background conditions. Confirm the required size with the responsible authority rather than assuming a default for all urban roads.
Consider a 300mm head where it matches the approved road design, required visibility and existing equipment. Urban arterial, collector and mixed vehicle-pedestrian installations require assessment of approach speed, viewing distance and the relevant authority rules, not a universal speed threshold. Arrow, bicycle and pedestrian indications must use the approved symbol and size for the project. Confirm that the housing, optical assembly and mounting hardware suit the specified indication and pole.
4. 400mm / 16 inch: high-speed and long viewing distance
Consider a 400mm (16 inch) signal only where it meets the applicable requirements and approved visibility design. Approach speed, viewing distance, background, mounting and the optical configuration all need review. Do not assume that every highway or high-speed approach requires 400mm, or that nominal diameter guarantees visibility beyond a specified distance.
Consider a 400mm signal where the approved project requires that size or its optical characteristics for the approach and viewing conditions. Confirm the actual assembly mass, wind area, mounting loads and electrical demand for the selected model. Check the pole, arm, brackets and cabinet supply against those values; neither a generic speed threshold nor an assumed head weight is a substitute for the project design.
5. Mixing diameters in one intersection
Using different head diameters at one intersection requires approval under the local design rules. Review each approach’s visibility, indication function and visual consistency; a higher approach speed alone does not establish permission to mix 200mm and 300mm heads. If considering 200mm and 400mm on the same approach, obtain an explicit design review rather than relying on a general rule.
Different signal sizes may appear within one intersection, but the approved layout should define the size, indication and position for each approach and user group. Check the authority’s visibility and installation requirements before combining vehicle and pedestrian heads. Use a consistent equipment schedule and drawing; do not treat an example size combination as automatic approval for another project.
6. How to choose: speed, distance, road type
Use the approach design speed, required viewing distance, road class, mounting position and background conditions when selecting signal diameter. Consider 200mm, 300mm and 400mm options only within the applicable authority requirements and approved design. Do not assign a universal diameter from speed or distance alone. Check the standards relevant to the project: product performance and installation requirements have different scopes. In China, GB14886 addresses signal setting and installation; confirm the applicable edition and the authority-approved configuration. Resolve conflicting requirements with the responsible designer and authority.
7. Other sizes GAOQIAO supplies
GAOQIAO supplies 100mm (4 inch) signal heads for compact installations. Assess the exact model’s optical performance, environmental rating and permitted application before specifying it for parking areas, bicycle routes, pedestrian facilities, garages or tunnels. Small size alone does not establish approval or suitability for a road or indoor location.
Frequently asked questions
What is the most common traffic light size?
200mm (8 inch), 300mm (12 inch) and 400mm (16 inch) are size options to assess against the applicable signal rules and approved design. Do not assume that a diameter is universally standard for pedestrian, bicycle, urban-vehicle or highway use.
Can I use 200mm heads on a main road?
Whether a 200mm signal is acceptable depends on the applicable authority requirements and approved design. Review approach speed, viewing distance, indication type and mounting conditions with the responsible designer. Do not apply a universal 50 km/h threshold or assume that every pedestrian or bicycle installation permits the same size.
What size do I need for a 60 km/h intersection?
For a 60 km/h approach, confirm the required signal visibility and diameter in the approved design. Consider viewing distance, background, geometry and tested optical performance; neither 300mm nor 400mm can be selected from speed or a single distance threshold alone.
Are 400mm heads worth the extra cost?
Where the approved design calls for a 400mm signal, assess its viewing performance, mounting loads, electrical demand and maintenance access. A 300mm signal may be considered where it meets the project’s requirements. Do not select either size from a universal speed, distance or fog threshold; compare compliant configurations and their complete costs.
Can I mix 200mm and 300mm heads?
Mixed signal diameters may be used where the approved layout and applicable authority requirements permit them. Assess visibility, indication consistency, position and mounting loads for each approach. Do not approve a mixed arrangement solely because one approach has a higher speed.
How big are traffic lights in real life?
Choose signal diameter from the applicable authority requirements and approved visibility design. A nominal 300mm or 400mm face size does not by itself establish viewing performance, overall dimensions or structural load. Confirm the optical assembly, housing dimensions and mounting requirements for each proposed option, and have the pole and arm checked for the actual assembly and design loads.
Does the diameter affect power consumption?
Power consumption depends on the selected optical unit and driver, not diameter alone. For a 12-lamp intersection comparison, use the actual input power and operating time of each active indication for the 200mm, 300mm or 400mm options. Check the complete network calculation before claiming an energy saving.
Relevant GAOQIAO products
These public GAOQIAO catalogue pages are related to the guide. Open them for the representative description, then confirm the latest drawing and configuration before ordering.
- 200mm (8 inch) LED traffic lightsCompact heads for pedestrian, bicycle and low-speed urban applications.
- 300mm (12 inch) LED traffic lightsStandard heads for urban arterials and signalised intersections.
- 400mm (16 inch) LED traffic lightsFor highways, motorway approaches or fog-prone sites, confirm signal-head size and visibility requirements in the approved design.
- Full LED traffic signal head collectionAsk about available 100mm, 200mm, 300mm and 400mm configurations and confirm compatible accessories for the selected model.