Because headlamps are something drivers use every day, we arranged with Truck-Lite to see if LED headlamps are really as good as they are reputed to be. Manufacturers such as Truck-Lite use sensitive instruments to measure light output and the like, but I just wanted to see with my own two eyes what kind of a difference they made in night vision.
Watching headlamps being assembled at Truck-Lite's Falconer, N.Y., plant, I was amazed at the size of the light-producing part of the assembly. There are six LEDs in each assembly, four in the low-beam reflector and two in the high. Each LED is no more than a quarter-inch square, which totally doesn't reconcile with the amount of light they produce. Truck-Lite says they will last about 30,000 hours — about 10 years of average service for an over-the-road truck.
The test procedure was pretty simple. We stopped the truck at the same spot on a dark, deserted stretch of road and took a few photographs from inside the cab to illustrate the difference between the two sets of headlights. We used the same Freightliner Cascadia day-cab, which underwent a headlamp transplant between the test runs. We replaced the entire assembly with the halogen lights with a module containing the LED lights.
The photos were taken with the same camera using the same settings, so the camera's exposure controls were nullified and would not affect the outcome. The settings for all the photos are as follows: Canon 5D in Manual mode; 24 mm focal length, ISO 400, 15-second exposure, manual white balance. In other words, what you see in the photos is what the camera saw; no digital trickery was applied after the fact.
What jumped out at me immediately was detail visible just off the road, where the trees are on the left in the LED photos. They were not even visible with the halogens. That gives a driver a real edge when it comes to spotting wildlife lurking at roadside or catching signage in the distance.
The difference was equally obvious on an Interstate highway. The wide roadway and the sloping roadside were beautifully lit. I think what truly made a difference was the color of the light. Truck-Lite says the color temperature of the LED light — the blue to red shift in the light spectrum — is very close to the color temperature of sunlight, around 6,000 degrees Kelvin, compared to halogen at around 4,000 K. Technically, they are not much "brighter," but they sure appear to be because of the color.
Interestingly, driving on a busier stretch of two-lane road with opposing traffic, not once did I get a flash of the high beams from oncoming cars annoyed by my brighter lights. I'm told this has a lot to do with the reflector design, which throws light where it's needed -- straight down the road and low and wide — rather than into the eyes of oncoming drivers.
While they are considerably more expensive up front than halogen headlamps, LEDs will long out-live the first service life of the truck and will give drivers night lighting like they have never seen before.