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SAE J593-2021: Enhancing Backup Lamp Photometry for Rear View Camera Systems
The SAE J593 standard for backup (reversing) lamps has been a cornerstone of vehicle lighting since 1947. The 2021 revision introduces critical updates to address the growing reliance on rear view camera systems, ensuring that backup lamps provide adequate illumination for the camera to produce a clear image at night. This article explores the key changes, including new photometric requirements, mounting height considerations, and design guidelines that engineers must understand to comply with modern rear visibility expectations.
Overview and Rationale
The revision was driven by feedback from vehicle manufacturers and the SAE Signaling and Marking Devices (SMD) Committee, which recognized that the existing photometric pattern did not guarantee an optimal nighttime camera image. With rear visibility systems mandated in many markets, the need for backup lamps to illuminate the area immediately behind the vehicle became critical. The task force studied the relationship between mounting height and ground illumination, leading to the introduction of a new photometric table for high-mounted lamps and the retention of the original table for low-mounted or camera-less vehicles.
🛠️ Key Insight: The 750 mm mounting height threshold aligns with other SAE lamp standards (e.g., front/rear turn signals, tail, stop), providing consistency across vehicle lighting systems.
Key Photometric Changes: Zone VII and Mounting Height Threshold
🔍 The most significant change is the addition of Zone VII to Figure 1, covering test points from 10° down to 20° down and 10° left to 10° right. This zone ensures that high-mounted backup lamps (≥750 mm) illuminate the area close to the vehicle, where camera test objects are located (0.3 m, 3.05 m, and 6.1 m behind). For lamps mounted below 750 mm, the original 5° down test points remain sufficient, as they intersect the ground closer to the vehicle.
| Mounting Height | Photometric Table | Key Downward Test Points | Ground Intersect (Example) |
|---|---|---|---|
| Low (< 750 mm) | Original (no Zone VII required) | 5° down (original) | ~4.6 m from vehicle (400 mm height) |
| High (≥ 750 mm) | New (includes Zone VII) | 20° down (Zone VII) | ~3.0 m from vehicle (1100 mm height) |
Note: Footnotes 7 and 8 allow vehicles with low mounting heights or GVWR > 4536 kg to use the original photometric table, even if equipped with a camera.
⚠️ Common Mistake: Using the original 5° down test points for high-mounted backup lamps (e.g., on liftgates) can result in poor illumination of the area immediately behind the vehicle, degrading camera image quality for distances critical to rear visibility compliance.
Design Guidelines and Engineering Insights
The 2021 revision also adds important design recommendations in Section 7.1.1 and 7.1.2:
- Uniformity of Light: Designers should aim for even light distribution on the road surface to avoid dark spots or glare that could impair camera performance.
- Red Light Interference: Red light from tail and stop lamps active during backing can wash out the white backup lamp output, degrading camera image hue and contrast. Engineers must consider the combined photometric effect when tail/stop lamps are illuminated simultaneously.
🛠️ Engineering Design Insight: To balance uniformity and glare, consider the optical design of the backup lamp (reflector, lens, LED arrangement) and its integration with adjacent lamps. Simulation tools should model the 20° down test points for high-mounted installations to ensure compliance with Zone VII. Additionally, the location of tail/stop lamps relative to backup lamps should be evaluated to minimize red light contamination on the camera sensor.
Frequently Asked Questions
1. Why was SAE J593 updated in 2021?
The update addresses inadequate illumination for nighttime rear view camera displays. The existing photometric pattern (5° down) did not sufficiently light the area immediately behind the vehicle for cameras, especially on high-mounted backup lamps.
2. What is the new photometric Zone VII?
Zone VII is a region of test points from 10° down to 20° down and 10° left to 10° right, added for backup lamps mounted 750 mm or more above the road surface. It ensures illumination of the ground close to the vehicle, covering the test object locations used in FMVSS 111 and CMVSS 111 rear visibility evaluations.
3. How does mounting height affect backup lamp performance?
Mounting height determines where the lamp’s downward test points intersect the ground. Lower lamps (< 750 mm) naturally illuminate the area near the vehicle; higher lamps (≥ 750 mm) require additional downward angles (e.g., 20°) to avoid illuminating too far behind the vehicle.
4. What should designers consider regarding red light interference?
When tail/stop lamps emit red light during a backing event, the combined red and white light can distort the camera image, reducing clarity. The standard recommends that vehicle manufacturers evaluate this effect and consider mitigation strategies, such as dimming or shutting off tail/stop lamps during reverse, or optimizing lamp placement.
For detailed photometric tables and installation requirements, refer to the full SAE J593-2021 document. Understanding these updates is essential for ensuring that backup lamps support modern rear visibility systems, improving safety and driver confidence during nighttime reversing maneuvers.
