LED headlight bulb tests
Yi-wei Liu and John Bullough of the Rensselaer Polytechnic Institute tested nine LED headlight bulbs in three DOT certified headlight assemblies. Their findings were published by the Society of Automotive Engineers (SAE) on April 2, 2019. The SAE paper is titled; Evaluation of After-Market Light Emitting Diode Headlight Bulbs.
Summary of the findings on LED headlight bulbs
The paper concludes that the use of LED bulbs in two different types of headlight assemblies designed for halogen single filament bulbs resulted in:
1) “Photometric measurements at several critical test points for headlight performance revealed that none of the resulting distributions met all of the test point photometric requirements.
Some Photographs of the resulting beam patterns for each combination of LED bulb and headlight unit, when compared to the patterns with the halogen bulb, revealed stark differences in performance between the halogen and LED bulbs.
2) “using after-market LEDs to replace halogen bulbs can compromise head lighting performance.”
3) “Even though some bulbs more closely matched halogen performance, performance for different headlights using the same LED bulb could vary widely.”
The LED headlight bulbs tested
The H11 style LED headlight bulbs tested are typical of the bulbs advertised by online sellers. None of the nine bulbs have markings showing they are U.S. Department of Transportation (DOT) certified. In addition, none of the bulbs conform to current federal headlighting regulations. In spite of that, some of the bulbs state they, “meet current regulations,” which is actually impossible. To get around current DOT regulations, some of the LED headlight bulbs are labeled for “off road use” only, which means they cannot be used on city streets or highways.
The LED bulb test procedure
The test used headlights assemblies designed and DOT certified for halogen single filament bulbs and then retrofitted with LED style headlight bulbs. Two conventional reflector type headlights that were visually optically aimed were used, as well as one projector type that was visually optically aimed.
The LED lights were cast onto a wall located 25-ft. from the test vehicle. The LED beam patterns and light intensity was measured in five locations and compared to the results from halogen bulbs using the same headlight assemblies.
LED headlight light output—advertised versus actual
All LED bulbs, household and automotive exhibit light intensity drop off after about 5-mins of use. The test showed that the nine automotive LED headlight bulbs exhibited a reduction in light output between 2% to 19% after 5-mins of use.
In addition to the 5-minute light drop off, seven of the nine bulbs showed substantially lower (18% to as much as 70% less) light output than their advertised ratings. Only one LED headlight bulb tested 3% higher than the manufacturer’s stated output. One bulb had no cold-temperature lumen rating.
LED headlight color
Light color is rated in degrees Kelvin.
Light from a candle is on the reddish side of the spectrum, usually measured at around 1850°K. A soft white household lamp bulb typically measures around 2550°K. Factory halogen headlight bulbs are slightly “bluer”, with a Kelvin rating of around 3100°K to 3400°K.
Upgraded “brigher” halogen bulbs typically measure closer to 4300-5000°K. Daylight measures around 5500°K.
High intensity discharge (HID) headlight bulb temperatures typically range from 4000°K to 5500°K. Since 5500 is the same temperature as daylight, the brain interprets 5500°K HID headlight color as white. However, HID “styling bulbs” are designed to produce light closer to 6000°K which the brain sees as blue.
All nine LED bulbs tested had an advertised correlated color temperature (CCT) range from 6000 to 6700 K. However, only two of the bulbs had a CCT within 200°K of their advertised values. Several bulbs differed by more than 100°K. All nine bulbs showed a higher CCT value than the manufacturer’s stated color temperature. In other words, they were even “bluer” than advertised.
LED headlight fit
Several of the test bulbs didn’t fit into the headlight units and were unable to be measured. In addition, the positioning of the multiple LED chips did not match even come close to matching the precise location or dimensions of a halogen bulb filament. The mis-positioning of the LED chips, by definition, means bulbs cannot cast light onto the road in the same pattern or the same intensity as a halogen bulb in a headlight DOT certified for halogen bulbs.
Rick’s take on the SAE paper and other LED facts
Here are my take aways from Evaluation of After-Market Light Emitting Diode Headlight Bulbs.
• You can’t rely on the lumen ratings published by the LED bulb manufacturer. The lumen output is exaggerated by as much as 70%! Caveat: the SAE studied only 9 LED bulbs.
• Retrofitting an LED headlight bulb into a headlight assembly DOT certified for halogen bulbs will NOT cast more light on the road. Other tests show that no matter how the headlight is re-aimed, LED and HID bulbs produce more glare to oncoming traffic.
• Retrofitting an LED headlight bulb into a headlight DOT certified for a halogen bulb is NOT legal, despite what the LED bulb maker claims. See this post.
• You expose yourself to legal liability if you install an LED or HID bulb in a halogen headlight and the light causes glare in oncoming traffic that results in an accident. You can bet the opposing attorneys will find out that you modified your headlights to bulbs that are not approved for your headlights.
• LED headlight bulbs may not even fit properly into your headlight assembly
• The life of LED headlight bulbs is nowhere close to the manufacturer’s estimated life. The cause of early failure is often caused by failure of the LED power module or cooling fan.
©, 2019 Rick Muscoplat