Light source characteristics

Light Source Characteristics
NHTSA Workshop
Headlamp Safety Metrics
Balancing Visibility and Glare
Dennis Holt
July 13, 2004
Light Source Technologies
„ Halogen / Incandescent
„ High Intensity Discharge (HID)
„ Light Emitting Diode (LED)
Global Automotive Lighting
Page 2
July 1, 2004
Light Source Characteristics
Primary
Characteristics
Secondary
Characteristics
„
„
„
„
„
„
„
„
„
Light Output (Lumens)
Luminance (Lumens / Area)
Dimensional Tolerance
Stray Light
Dual / Single Filament
Spectrum
Lumen Maintenance
Energy Efficiency
Reliability
These characteristics are important to headlamp design impacting
many aspects of system performance including glare and visibility!
These factors are changing with new and evolving technologies.
Global Automotive Lighting
Page 3
July 1, 2004
Increased Light Output (Bulb Lumens)
Visibility
Glare
Distance Vision (Hot Spot)
Peripheral Vision (Spread)
Foreground Light
Scattered Light
Other
Beam Uniformity
¾ Halogen
¾ HID
¾ LED
1000 to1500 Lumens
3000 Lumens
30 to 200 Lumens (multiple required)
More light permits a better beam pattern
Global Automotive Lighting
Page 4
July 1, 2004
Increased Luminance (Lumens / Area)
Visibility
Glare
Distance Vision (Hot Spot)
Negligible Impact
The beam pattern is formed
by stacking up multiple
source images
¾ Halogen
¾ HID
¾ LED
15-25 cd/mm2
70 cd/mm2
5 to 15 cd/mm2 (Progressing Rapidly)
Higher luminance permits better distance vision
Global Automotive Lighting
Page 5
July 1, 2004
Tighter Dimensional Tolerance
of the Source to the Reflector
Visibility
Glare
Better Formed Beam Pattern
Distance Vision (Hot Spot)
Beam Control (focus)
Other
Headlamp Design Freedom
¾ Halogen +/- 0.9 to 0.2 mm (improved w/ new bulb designs)
¾ HID
+/- 0.5 mm
¾ LED
Too Early to Tell (multiple source challenge)
Better tolerances and optical referencing result in better
headlamp performance and design possibilities
Global Automotive Lighting
Page 6
July 1, 2004
Reduced Stray Light
Visibility
Glare
Adverse Weather Driving
Scattered Light
Other
Lower Cost & Complexity of Headlamp System
¾ Halogen
¾ HID
¾ LED
Better Performance From New Designs
Good Performance
Too Early to Tell
Reduced stray light means better control and reduced glare
Global Automotive Lighting
Page 7
July 1, 2004
Dual Filament vs. Single Filament
Visibility
Glare
Optical Tradeoffs Required
Shadows
Scattered Light (Reflections)
Other
Smaller Headlamp Possible
Lower Cost & Complexity
¾ Halogen Dual & Single Filament Available
¾ HID
Dual Filament Functionality w/ added hardware
¾ LED
Individual Control of Multiple Sources
The two approaches offer different costs and benefits
Global Automotive Lighting
Page 8
July 1, 2004
Spectrum Uniformity
Visibility
Glare
Object Recognition
(Color Rendering)
¾ Halogen
CRI = 100
¾ HID
CRI = 65
¾ LED
CRI = 70
Negligible Impact
Higher CRI is desirable, but it does not affect performance
Global Automotive Lighting
Page 9
July 1, 2004
Spectrum:
Short Wavelength Content
Visibility
Glare
Peripheral Vision (Rod Cell)
Discomfort Glare
Halogen
Other
Styling
¾ Halogen Little light at short wavelengths
¾ HID
Greater light at short wavelengths
¾ LED
Greater light at short wavelengths
HID
LED
Wavelength is a trade-off between peripheral vision & glare
Global Automotive Lighting
Page 10
July 1, 2004
Improved Lumen Maintenance
Visibility
Glare
More Light for Old Cars
¾ Halogen
¾ HID
¾ LED
Negligible Impact
70% at 2000 hrs (Beyond the life of many halogen sources)
80% at 2000 hrs
Too Early to Tell (~Life of Vehicle)
New Technology will provide better long term performance
Global Automotive Lighting
Page 11
July 1, 2004
Increased Energy Efficiency
Visibility
Glare
Better Performance From HID
Negligible Impact
Other
Fuel Economy
¾ Halogen
¾ HID
¾ LED
Baseline
~ 3 x Halogen
Similar to Halogen (Progressing Rapidly)
Higher efficiency can drive vehicle system savings
Global Automotive Lighting
Page 12
July 1, 2004
Increased Reliability
Visibility
Glare
Negligible Impact
Negligible Impact
Other
Lower Warranty
¾ Halogen
¾ HID
¾ LED
Baseline
~ 3 x Halogen (Life of Vehicle)
Too Early to Tell (~Life of Vehicle)
Better reliability reduces the number of cars with failed lights
Global Automotive Lighting
Page 13
July 1, 2004
System Interactions & Conclusions
Visibility
Glare
Significant
Significant
¾
¾
¾
¾
Voltage Sensitivity
Vibration Sensitivity
Tolerance of Matching Parts
Switching & Operating Cycle
„ New Technology
Provides Improved Capability
„ System Interactions
Performance Requires Team Work
„ Tradeoffs
Light Source Design & Application
is a Balance
Global Automotive Lighting
Page 14
July 1, 2004
Any Questions?
Global Automotive Lighting
Page 15
July 1, 2004
Download PDF
Similar pages