Ford Kerosene Car Lamp
Calcium Carbide Car Lamp
Original automotive headlights burned kerosene, had a chimney, needed to be lit and extinguished. Headlight innovations around the same time gave calcium carbide generators, with a controlled water drip, produced Acetylene Gas, which, when burned, produced intense light, greatly improving a car's nighttime vision.
Today we don't have to re-fuel our headlights. Instead we enjoy LED lamps rated at 50,000 hrs, or 5 years of continual operation. In the past 2-3 years the industry has made great strides in integrating high performance LEDs in all vehicles. From side markers, to taillights, to the interior LEDs are becoming the standard. Like the LED lightbulb replacing standard bulbs, all auto lamps are headed to obsolescence.
The "holy grail" of automotive lighting has been to replace headlight lamps with an LED solution. A legitimate LED swap has been completely unheard of until now. The doors have flung open with the recent milestone in LED brightness output of 100 lumens per Watt, and further with some manufacturers demonstrating 200 lm/W in laboratories. Cars need over 800 lumens for proper headlight usage, and these LEDs are up to the task. For example, a single Cree XLamp XP-G Cree XLamp XP-G series LED can provide 400 Lumens at 1A and over 130 lm/W at 350mA. Driving the LED at 1A produces the maximum amount of heat, the number one issue with LED systems.
However, price has completely blocked the wide automotive adoption of LEDs. Just a few years ago, a single LED would cost $5.00 USD, in the past year has dropped to $1.00 USD. The sweet spot of price and ease of manufacturing should be hit in the coming 12 months. Despite initial cost, overall lifetime cost and environmental impact will over pay for itself. A regular halogen lamp, single beam, requires 55 watts (240 watts on high beam). The more efficient Xenon lamp needs 35 watts. Average power input need for LED lamps comes in at 28 watts per beam. The overall efficiency is only getting better. Volkswagen plans to introduce OSRAM Joule JFL2 LED systems into their headlamps promising only 19 watts per beam. Environmental impact also pushes adoption. On conventional cars, with LED lamps, 196 grams of carbon dioxide per 100Km (62 miles), compared to 768 grams per 100Km with halogen bulbs.
Plug-in and Hybrid vehicles benefit the most from LED lamp adoption. Up to 6 miles is added to a hybrid car's electric only range with the use of LED headlights. 19-28 watts is a far cry from the 55 - 240 watts needed with halogen bulbs. Toyota/Lexus was the first to offer LED lamps as an option, followed by Audi, Cadallac, and 2011 has most car manufacturers promising LED options. Most LEDs options are used for daytime running lights at the moment, but full beam implementation is close. As brightness levels increase and modules prices decrease, adoption for full headlight usage will become market standard. As of 2011, 3rd generation Toyota Prius, Nissan Leaf, and Mitsubishi i-MiEV will have full beam LED headlight options.
Efficiently driving and regulating an array of LEDs in a headlight is the main design difficulty. A few ICs are available now to drop right into the application. Linear Technologies has a DC/DC converter, LT3956, designed to operate as a constant-current and constant-voltage regulator, ideal for high brightness/high driving current LEDs. In particular, a 25 W white LED headlight lamp can be configures with 18 of the Cree XLamp XP Cree XLamp XP (130lm/W at 350mA) series elements. The LT3956 LT3956 outputs a PWM signal ranging from 100kHz to 1MHz, giving the user a dimmable ratio of 3000:1. Due to its tunable features, the LT3956EUHE#PBF LT3956EUHE#PBF is up to a 94% efficient. Drives LEDs in Boost, Buck Mode, Buck-Boost Mode, SEPIC or Flyback Topology. However the 6% in efficiency, or 1.5W (25W*0.06), is dissipated as heat, even with the UHE package (5mm x 6mm) heat-sinking is inevitable.
Another option is the Renesas LED headlight driver, μPD168891, which can provide constant-current control for up to 12 LEDs in series. Renesas's IC has built in overcurrent protection, diagnostic functions, emergency shutoff to prevent current issues, and is in a 48-pin VQFN package to reduce heat generation. A few others ICs exist, but no one chip is the end-all option in this fledgling industry. Choosing the right components is based on individual design requirements, and should be chosen accordingly.
A mere 100 years after the kerosene headlight, the automotive lighting has grown to be an over 10 Billion USD industry. Electrically efficient high lumen LEDs made it possible, and more of them are coming every quarter. With few components available in this relatively new automotive LED Lighting industry, the brave and the willing to get up to speed in a very short amount of time. Very few times in technological advances can someone start at the leading edge of an industry without extensive training. The building blocks are here, they just need someone to put them together.
Cabe
Personal automotive lighting design story:
I started in the automotive industry designing a side (turn) lamp systems for a future hybrid. What I discovered is nothing more than V = I*R is needed for me to begin that career path. At first I was meticulous and cautions about power regulation, but eventually it came down to just matching a resistor to a LED ( R = V/I ). A later incarnation of my circuit used a driver IC like mentioned above, all I had was a datasheet. The prototype was finished and on its way to being part of the LED Auto Revolution. I will say with my first hand experience, the industry needs more engineers.
