In general, today’s innovations in exterior lighting increase roadway safety and reduce vehicle power consumption—thereby lowering CO2 emissions.Average usage times of the different light functions are commonly known from statistical monitoring by carmakers and suppliers. The following usage rates (on-time as a percentage of vehicle usage) are accepted by CLEPA as reasonable average values:
• DRL 64%,
• Low-Beam 33%,
• Front position, tail light and licence plate illumination 36%,
• Front/rear turn function 15%,
• Stop light 11%
In terms of energy consumption (power × usage) the low-beam and the DRL functions are the major contributors. Today, these functions are usually not on during European fuel consumption and emission type approval tests (NEDC). In the United States, GM successfully lobbied for permission to disable their vehicles’ DRLs during Federal emissions and fuel consumption certification tests; all GM vehicles come with DRLs though U.S. law does not require them.
Exterior lighting equipment has a relatively high degree of standardisation. Therefore the power consumption of the different light functions is basically independent on the size of vehicles. The potential CO2 savings by efficient lighting technologies (e.g. Xenon HID in low/high-beam and LED in other lighting functions) can be determined and translated in relative savings for the individual segments by relating to the average emissions of the different segments [%].
Due to the long usage times DRL is a main driver of energy consumption among the different lighting functions. Therefore replacing conventional DRL by LED DRL is the most cost efficient way to realize significant reductions of CO2 emissions.
Realising other lighting functions in an energy-efficient way using HID and LED technology will be less cost-effective due to lower power reduction potential, lower usage times and/or higher costs, but will increase total CO2 emission reductions by a factor 2 to 3. Mixed scenarios using different technologies are possible (see fig. below).
HID and LED increase total lighting CO2 emission reductions by a factor 2 to 3
