Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Headlamp Mounting Height for Passenger and Pickup Truck Vehicles: Insights from SAE J2584-2011
Background and Rationale: The Growing Problem of Mirror Glare
In the late 1990s, increased popularity of sport utility vehicles (SUVs) and pickup trucks led to rising public dissatisfaction with glare from high-mounted headlamps. NHTSA received numerous complaints regarding both rear and frontal glare, particularly from side mirrors. Unlike interior rearview mirrors, side mirrors cannot be easily dimmed, making side mirror glare a persistent issue. In response, the SAE Mounting Height Task Force was reconvened in 1999 to evaluate the problem and determine appropriate headlamp mounting heights to control mirror glare for passenger vehicles and pickup trucks—a scope initially omitted from earlier heavy-truck recommendations (SAE J2338).
This technical report, stabilized in 2011, compiles research on discomfort glare and provides a framework for establishing mounting height limits that balance visibility and comfort for all road users.
Discomfort Glare Research and Acceptable Limits
The task force reviewed several pivotal studies to quantify the level of glare that drivers find acceptable. These studies used the De Boer Glare Rating Scale, where 1 = unbearable, 5 = just acceptable, and 9 = just noticeable.
Key findings include:
- Miller et al. (1974) estimated that drivers accept near‑foveal illuminance of 0.4–1.6 lux (after accounting for windshield transmittance). Side mirrors were exposed to 1.9 lux from normally aimed headlamps and up to 11.9 lux when misaimed.
- Olson and Sivak (1984) studied peripheral glare from side mirrors and found that “just acceptable” discomfort (De Boer 5) corresponded to eyepoint illuminance of 2.37–8.61 lux, depending on exposure duration.
- Sivak et al. (1997) determined that for oncoming glare at 3.5°, the just‑admissible level sits at 3–4 lux for short exposures.
- Schmidt‑Clausen and Bindels (1974) established that discomfort glare is inversely proportional to the 0.46 power of the peripheral angle from the point of focus.
| Study | Glare Type | Illuminance Range (lux) | De Boer Level | Key Finding |
|---|---|---|---|---|
| Miller et al. (1974) | Direct (foveal) | 0.4–1.6 | Acceptable | Drivers tolerate near‑foveal glare up to ~1.6 lux |
| Olson & Sivak (1984) | Peripheral (side mirror) | 2.37–8.61 | 5 (just acceptable) | Side mirror glare acceptable at these levels for various durations |
| Sivak et al. (1997) | Oncoming (3.5°) | 3–4 | 5–4 | “Just admissible” level for short exposures |
| Schmidt‑Clausen & Bindels (1974) | Peripheral (variable angle) | Varies with angle | N/A | Discomfort ∝ angle–0.46 |
The task force synthesized these results to define acceptable discomfort limits for side mirror glare. Exposure duration markedly increases discomfort: a 10‑ to 20‑second exposure degrades comfort by about one De Boer unit, and a three‑minute exposure by roughly 2.5 units. Therefore, mounting height recommendations must consider real‑world exposure times typical of nighttime driving.
🔍 Engineering Design Insight: Side mirror glare is more challenging than interior mirror glare because drivers cannot dim the side mirror to reduce discomfort. Moreover, the peripheral portion of glare— while less debilitating than direct glare—still causes significant discomfort and must be mitigated by controlling headlamp mounting height. The Schmidt‑Clausen and Bindels relationship shows that increasing the peripheral angle (e.g., by lowering headlamp height) reduces discomfort glare proportionally to the 0.46 power of that angle.
Frequently Asked Questions
Why does headlamp mounting height affect side mirror glare?
When headlamps are mounted high (as on many SUVs and pickup trucks), their light directly enters the side mirrors of lower vehicles at a small vertical angle. This creates intense peripheral glare that cannot be dimmed easily. Lowering the mounting height reduces this angular alignment and brings the glare into a less‑sensitive peripheral field.
What is the De Boer glare rating scale?
The De Boer scale rates discomfort glare from 1 (unbearable) to 9 (just noticeable). The odd numbers have verbal qualifiers: 1 – unbearable, 3 – disturbing, 5 – just acceptable, 7 – satisfactory, 9 – just noticeable. SAE J2584 uses this scale as a reference for setting acceptable glare limits.
How does exposure duration influence acceptable glare levels?
Longer exposure worsens discomfort. For example, an illuminance that is “just acceptable” for a 3‑second glance becomes “disturbing” after 20 seconds. The report provides an algorithm (De Boer rating = 5.05 – 1.405·log exposure seconds) to adjust acceptable levels based on time.
Did SAE J2584 recommend a specific mounting height for passenger vehicles and pickup trucks?
The report focuses on establishing the engineering basis for such a limit. It does not prescribe a single height, but the analysis supports limiting mounting height to approximately 0.9–1.0 m, similar to the earlier heavy‑truck recommendation in SAE J2338. The key is maintaining a sufficient vertical differential between the headlamp center and the mirror eye level of other vehicles to keep glare within the acceptable range.
⚠️ Note on Headlamp Aim: Misaimed headlamps can dramatically increase glare—from 1.9 lux to 11.9 lux in side mirrors, as shown in the Miller et al. study. Proper aim is essential to achieving the intended performance from any mounting height design.
