Performance of Headlights Fitted with LED Replacement Bulbs

To ensure adequate visibility without excessive glare, vehicle headlights are designed to use a specific source of illumination. The optical designs of headlights gather the luminous flux produced by the light source to produce a useful beam pattern that meets the relevant requirements and standards for vehicle forward lighting. With the advent of solid state, light emitting diode sources for general illumination, an increasing number of LED replacement headlight bulb products has emerged over the past decade. In most cases, these LED replacement bulbs are not permitted for legal use on public roadways, but some countries have begun to permit specific LED replacement bulbs to be used legally on the road for specific makes, models and production years of certain vehicles. If they can be demonstrated to produce a beam pattern that meets the photometric requirements for a legal headlight, they are permitted to be used legally for on-road use. In the present paper we present photometric measurement data for two North American headlight systems originally designed for halogen bulbs. Each was fitted with a halogen bulb and with two different LED replacement bulbs and measured at specific angles to check photometric compliance with the minimum and/or maximum luminous intensity at those angles. We also present data on the illuminances produced at several locations along a hypothetical roadway to compare performance between the headlights with halogen bulbs and with each LED bulb.