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(R) Tail Lamp (Rear Position Lamp) for Use on Motor Vehicles Less than, Equal to, or Greater than 2032 mm in Overall Width
The 2023 revision of SAE J585 marks a significant consolidation in automotive lighting standards. By merging the former SAE J2040, this standard now provides a single set of test procedures, requirements, and guidelines for tail lamps (rear position lamps) used on motor vehicles less than, equal to, or greater than 2032 mm in overall width. This merger eliminates redundancy and simplifies compliance for manufacturers serving diverse vehicle segments. 🛠️
Key Takeaway: J585 now covers all three width categories. Always check the “Scope” (Section 1) and the applicable test documents referenced (especially SAE J2139 for vehicles >2032 mm).
Scope and Key Updates
The standard’s scope explicitly includes vehicles of any overall width (≤2032 mm, =2032 mm, or >2032 mm). The Rationale notes that J585 supersedes J585 JUN2014 and merges the content of SAE J2040, which will become obsolete. Among the most important updates:
- New definitions: “Tail light function” (Section 3.1) is now clearly distinguished from “tail lamp” (Section 3.2).
- Lighting identification codes: “T” and “T2” codes (Section 4) differentiate photometric requirements—T2 being for larger lamps with higher performance demands.
- Test references updated: For vehicles >2032 mm, SAE J2139 (Tests for Signal and Marking Devices on Vehicles 2032 mm or More in Overall Width) is now required.
- Harmonization: UN Regulation R148 is added as a related document, aligning SAE with international practices.
⚠️ Common mistake: Assuming J585 still only applies to vehicles <2032 mm. The 2023 version covers all widths. Verify your product’s width class and apply the correct vibration, moisture, dust, and corrosion tests accordingly.
Testing and Performance Requirements
All tail lamps must pass a suite of environmental and photometric tests. The following table summarizes the mandatory tests and their applicable vehicle width scope:
| Test | Applicable Standard/Procedure | Vehicles <2032 mm | Vehicles ≥2032 mm |
|---|---|---|---|
| Vibration | SAE J575 (vehicles <2032 mm) / SAE J2139 (>2032 mm) | ✔ | ✔ (J2139) |
| Moisture, Dust, Corrosion | Per SAE J575 or SAE J2139 as applicable | ✔ | ✔ |
| Photometry (T / T2) | Figures 1, 2, 3 in J585 | ✔ | ✔ |
| Warpage | Section 6.1.6 | ✔ | ✔ |
Color requirements: The tail light function must be red, measured per SAE J578 (Chromaticity Requirements for Ground Vehicle Lamps and Lighting Equipment).
Photometric details: For lamps identified “T”, Figures 2 and 3 set minimum luminous intensity for three size classes, while “T2” lamps follow Figure 1 (with higher minimums). The maximum intensity at any test point is capped at 20 cd or 25 cd depending on the lamp size.
Engineering Design Insight: The new T2 code was introduced specifically for larger lamps (e.g., those on heavy trucks >2032 mm wide). Using the wrong code will lead to photometric non‑compliance because the minimum candela values differ. Always confirm the lamp’s “Lighting Identification Code” during the design phase.
Design and Installation Insights
Beyond testing, J585 provides design constraints and installation guidelines that directly affect vehicle integration:
- Optical area minimum: For T2 lamps, a minimum illuminated surface area is required (Section 6.4.3) to ensure sufficient visibility.
- Visibility zones: Figure 4 defines “unobstructed projected area” and Figure 5 gives luminous intensity guidelines to ensure the tail lamp is visible from the required rearward field.
- Installation location: Section 7.1.1 now clarifies that for vehicles <2032 mm, the lamp must be mounted at a certain height and width (references to “width” removed to align with the broader scope).
- Material durability: Plastic lenses must meet SAE J576, and the light source retention system must satisfy SAE J567 (now referenced in related documents).
Frequently Asked Questions
- 1. What is the difference between “T” and “T2” lighting identification codes?
- T is used for standard tail lamps on vehicles of any width, with size categories (1, 2, 3) setting photometric minimums. T2 is a higher‑output code for lamps that must meet elevated minimum luminous intensities (Figure 1) and a minimum optical area. The choice depends on the lamp’s design and intended vehicle width classification.
- 2. Which test methods apply to tail lamps for vehicles >2032 mm?
- For vehicles greater than 2032 mm, the vibration, moisture, dust, and corrosion tests must be performed per SAE J2139 instead of SAE J575. Photometric tests still follow J585’s figures, but the environmental conditioning is different.
- 3. What color is required for the tail light function?
- The tail light function must be red, with chromaticity tested according to SAE J578. No other color is permitted for the rear position lamp.
- 4. How does the merger of J2040 affect existing certifications?
- Products originally certified to J2040 may need re‑certification to J585 because the test references and some requirements have changed (e.g., addition of T2 code, updated photometric tables). Check with your certifying agency for transition timelines.
By unifying the requirements for all vehicle widths, the new SAE J585 (2023) simplifies compliance and aligns with global regulatory trends. Engineers should pay close attention to the lighting identification code (T vs. T2) and the applicable test standard (J575 vs. J2139) based on the vehicle’s overall width. 📐
