Principles of Headlightsof Headlamps
Illinois Association of Technical Accident Investigators
Springfield, IL
“How Far Do Headlights
• Torches, candles and oil lanterns were
invented long before automobiles
cave after dark?
The Need for Headlamps
operating at night was going to happen
• As more “horseless carriages began to
operate day and night, there were two
needs: To See and to be Seen
Acetylene
• CaC2 + 2 H2O → C2H2 + Ca(OH)2
• Used in miners’ lamps
accumulated methane.
(https://www.youtube.com/watch?v=pyFTijbsZzo)
• Acetylene produces a much brighter flame
• Almost no soot, just CO2 and H2O
• Introduced as auto headlamp in the 1880s
• Enclosed in a metal and glass fixture, the
flame was now resistant to wind and rain
• With parabolic mirror to concentrate the
light, faster vehicle speeds (5 mph?)
And other parts…
• But, it was not enough to have a lamp, you
had to have an acetylene generator, too.
• A container for the calcium carbide
• A water tank
difficult to safely start
• With electricity already available, electric
lamps were a natural accessory.
• First used on an electric Columbia around
1900
Much Better
relatively the weak dynamos that could fit
in a car
controlled from the cockpit, light from the
lamps was dim and the lamps often broke
Lens-Focused Headlamp
• Based on lenses used in lighthouses and
other lens based systems
lens, the lamp used lens segments and a rear
mirror
lighting
• By 1912, Cadillac had a complete electrical
system including ignition similar to what
we have today
with problems
became a problem
Lamp in 1915, physically aiming the lamp
down
• Driver had to go outside to do it.
• In 1917, Cadillac put a lever in the cab
Dual Filaments Lamps
Bilux lamp. Fixed mirror and lens, but one
off-set filament.
pattern.
use today
images.
images of the filaments on the road ahead
• One filament on the optical axis, and one
offset above.
where to place images
individually assembled and therefore
distribution
all the optical parts were rigidly fixed.
Filaments, Mirrors and Lenses
• Sealed beam lamps used one or two
filaments, a smooth parabolic mirror and a
front glass cover with molded-in “lenslets”
• With defined mounting nubs on the back,
the entire assembly was properly fixed to
the car
entire lamp assembly vertically and
horizontally
FMVSS 108
of the vehicle
controlled
motor vehicles would use the same 7”
diameter sealed beam lamps
standardized and sealed beams did not
(mostly) leak and fail.
is inhibited somewhat.
Tungsten Filament Lamps
• Blackbody radiation spectrum
• Temperature is controlled by current,
therefore applied voltage
coat envelope with black layer
• Therefore, lamps lose luminous output
• Filaments lose mass, thin and finally break
Four solutions
or breaks
• 4) Change to a tungsten/halogen lamp
The Halogen Cycle
• Cl, Br or I in gaseous form in the envelope
• At moderate temps, the halogen reacts with
(“gets”) free tungsten (W) atoms, forming a
tungsten halide compound & keeping
• At higher temperatures, near the filament,
the compound dissociates and redeposits
tungsten on the filament…someplace
• Ultimately, the filament still does thin and
break, just much later
• First used in Europe in 1962, in the US in
1983 (9004/HB1)
gases extended the useful life of the bulb
• With more power, quartz envelopes were
needed to resist higher temperatures
• Higher pressure, higher temperature, higher
output efficiencies over a longer life
Break Time
• FMVSS 108 (49 CFR 571.108) requires
various lighting systems to comply with
certain standards published to address each
system
standard is SAE J1383, Performance
Requirements for Motor Vehicle Headlamps
J1383
headlamp
stream of commerce
state statutes*
The Low Beam Pattern
• Red: maxima; Blue: minima
glare
retro-reflective signs
spot”
*J1383 Revised May 2010
*J1383 Revised May 2010
• Reflectance (dimensionless)
• There are other terms that are useful in lighting and visibility analysis,
but we will not cover them here
Intensity
• Measured in candela
• A candela: “The luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and has a radiant intensity in that same direction of 1/683 watt per steradian.”
• Simply: about one candle
Illuminance
• One foot-candle = 1 lumen/ft2
• One lux = 1 lumen/m2
• Formal definition: One lumen per unit area
• English system: Foot-candle
• Metric system: Lux
One Foot-candle
A card 1 foot from a 1 candela source receives 1 foot-candle of illuminance.
One lux
The wall 1 meter from the 1 candela source receives one lux of illuminance.
1 foot-candle
1 lux
is reflected from a surface
• Dimensionless, ranging from 0.0 to 1.0
• Matte: freshly fallen snow ρ = 1.0
: black velvet ~ 0.0
FMVSS 108 & J1383
• Without special dispensation, any motor
vehicle put into the stream of commerce
must comply with J1383
vehicle manufacturer and therefore to the
buyer.
with an approved test standard
• Page 3 of J1383 Rev May 2010 promulgates
amongst other documents J575 Test
Methods and Equipment…
you don’t have a test standard?
Current Technology
needed)
• Low cost bulbs, owner replaceable
• Luminous flux decreases over time
• Extended filament limits focus, designer
options
SilverStar® Bulbs
standard tungsten bulbs
brightest downroad halogen headlights in
our entire family of products.”
• In 2009, we tested OEM tungsten bulbs,
new tungsten bulbs and SilverStar® bulbs in
the same vehicle
• Encourages buyers that the bluish tone
actually improves the amount of
illumination on the road
and “see better”
• For HID “wannabes”
electrical power
the bulb will burn out sooner
• Same pattern, just less light…although
“bluer”, no surprise since mirror/lens
determine pattern
of 1999 Chevrolet Tahoe lamps
Results Make Sense
radiation spectrum
filter
effect because the eye is more sensitive to
yellow than blue
small electrodes
treated as a “point source”
• Hence, optical designers can put light
exactly where they want it and nowhere else
Arc Tube
HID Properties
• Instant ON/OFF
• More efficient
HID Color Temperature
• Dull red: < 2000; Yellow: ~3000°K; Blue:
5000°K
color temp can be “tuned”
• Most HID lamps emulate daylight with a
very blue color temperature
Claims that HID “dazzles”
light more than red, yellow light
• But, this is for a given input intensity
• With sharp cutoff that HID lamps offer, the
opposing driver usually sees less input
intensity, therefore less glare
tungsten/halogen lamps draws attention
Light Emitting Diodes (LED)
• Low voltage as compared with HID
• With a variety of diodes in various
locations, designers can choose where to put
light and when to put it there.
• Cutouts can be created to prevent glare in
opposing or leading drivers’ eyes
LED pros/cons
– Solid state, often no moving parts
– Long-life, probably longer than the life of the
car
• Cons
– Expensive to replace
• A blue or even UV laser radiates phosphor
patches that are in the object plane of a
projector.
luminous patches onto the road ahead
• Computer control of which patches are
radiated and with how much power
Laser Headlamp Advantages
scanning mirror to essentially create array
• Imaging systems watch the road ahead
• Choose where and when to put light at
specific angles
replaced, if necessary
• Low power
calcium carbide
• “Recognize” oncoming and leading cars and
cut notches around them, or lower intensity.
• Software updatable as transportation
standards
• Test drive new cars at night to see how you
respond to new lighting technologies
• Sharp cutoffs in low beam pattern can
severely limit visibility in the upper FOV
HID vs LED vs LASER
• I prefer the LED lighting on my 2016 Mini
Cooper.
opposing drivers, not just point sources
• Remember, headlights are for seeing…and
to be seen.
have not yet
• There may soon come a day when you don’t
have the option to choose OFF, PARK,
LOW and HIGH.
you
need headlamps?
shall use a distribution of light or composite
beam directed high enough and of sufficient
intensity to reveal persons and vehicles at a
safe distance in advance of the vehicle.”
• So what is “safe”?
on if you need to get stopped? 1.0, 0.7, 0.5
or…how a comfortable 0.2?
DRIVE ON HIGH BEAM
UNTIL YOU CAN’T
that at only ground level
• High beams (when new) provide 0.3 foot-
candles to a minimum of 516 feet and
maximum of 966 feet
attention to the situation ahead
• Driving on high beam forces you to pay
attention to the situation ahead
Questions/Answers