Blinded by the Light? Comparing New LED Headlamps with HID/Xenon, Halogen
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Be prepared to encounter a new kind of bright headlamps coming at you on the road. I recently ventured out to GM's Milford, Michigan, Proving Ground to try out the Cadillac Escalade Platinum's spanking new LED low- and high-beam headlights. Cadillac is the first to offer light-emitting diodes for low- and high-beam lights and turn signals in the U.S. (Audi's European R8 also offers them, and the Lexus LS 600h uses LED for its low-beams only).
LEDs promise daylight-bright illumination with low current draw and unprecedented packaging and styling flexibility. They're little silicon computer chips, so they're relatively slim by nature and they can conform to unusual shapes, though they still need to shine through a lens of some sort. Cadillac has adopted them for its ne-plus-ultra flagship model, arranging the LEDs in a narrow vertical stack to match the vertical taillamps that have become a signature design motif (they're also LEDs).
Each Cadillac headlamp includes five LED arrays and lenses to cover the low-beam pattern and two for high-beam, with each of the seven units dedicated to lighting up a particular area of the road. LEDs throw little or no infrared heat forward (stick your hand in front of most any headlight and it'll feel warm -- not the LEDs), but the chips generate heat that has to be removed, so they have finned heat-sinks like many computers use, with a fan that circulates cooling air (in the winter, this helps defog and de-ice the headlamps). Further development will reduce the heat generated, resulting in lower energy consumption than High-Intensity Discharge (aka Xenon), but for now they draw just a bit less than Halogen bulbs.
We got the chance to compare the Platinum's LED headlamps against the Escalade's standard HIDs and against a Yukon Denali's halogen compound-reflector lamps. From the driver's seat the illumination is amazing. The "color temperature" of the light is about 6000 Kelvin (10,340 *** which is whiter than daylight (5600K). HID lamps, the ones that look bluer, are 4500K. At the bottom of the scale is the yellower looking light of your halogen headlight bulbs (3200K) and plain incandescent foglamps (2800K).
The light reflected back from roadside signs seems much brighter with LED than HID. The HID lamps illuminate the sides of the road more brightly and their high-beam pattern is like a huge cone of light reaching quite high. This is in part because each lamp produces more lumens of light -- about 2500 to the LED's 2000 total, though the total light perceived on the road is roughly equivalent. That means the LEDs must focus their light right where it's needed, so there's less sideways scatter and the high-beam pattern appears maybe twice the vehicle's height and four-lanes wide at a quarter-mile distance. The upper cut-off of the low-beam light pattern seems sharper on the HIDs, because there is a sort of "eyelid" cutting it off until you turn on the high beams. LEDs light up the same pattern on the road, but the edge of the light is less sharply defined. By comparison, the halogen beams appear dangerously inadequate -- a pool of yellow light right in front of the truck with far less reflection coming back from road signs, less side illumination, weaker high-beams, etc.
Cost is the big unknown. All anyone is saying is that it's "considerably more" than HID at the moment, though with time and volume production LEDs should achieve parity or become cheaper. The Platinum model costs $10,705 more than an Escalade optioned as close as possible to the Platinum's equipment level. Along with the LED lamps, that premium pays for unique front-end styling that apes the CTS's, a four-screen rear-seat entertainment system that can play something different on each screen, heated and cooled cupholders, a special overhead console, spectacular two-tone inlaid wood and handsewn leather trim on the dash and door panels, plus glove-soft aniline leather seating surfaces. The LED chips are expected to last the life of the vehicle and the cooling fans are replaceable if they fail, in which case the light dims by 20% to prevent damage if the temperature tops 300 F. If the chips fail or the unit suffers crash damage, a replacement lamp assembly part will cost about $1500 (which may or may not be subsidized).
How do they look to opposing traffic? Utterly blinding in high-beam mode, though not much worse than HID high-beams. The low beams don't look blue and there isn't too much glare, but the unusually tall stack of lights is sure to be perceived by oncoming motorists as high-beams. One flash of the Platinum's REAL brights will set lamp-flashers straight, pronto. I expect LEDs to propagate slowly through the market. Within three to five years, the light output per energy input should improve by 50%, which will make LED a fuel-savings feature. In the more distant future, LED lighting can provide adaptive illumination with no motors or moving parts, turning different LEDs on and off to provide cornering illumination and to alter the light pattern and prevent glare in approaching vehicles or even in the rearview mirrors of a car ahead (no Escalades currently offer adaptive front lighting to illuminate the direction the vehicle is turning). And I'm hopeful that by then, affordable LED-powered replacements for sealed-beam headlights will bring high-performance illumination to old-car hobbyists like me.
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