Genplus

A daytime running Light ,also called DRL or daytime running lamp. It is an automotive lighting on the front of a road going motor vehicle, installed in pairs.  

Daytime running lights are designed to switch on automatically when the engine is started – all other lights remain switched off. Conversely, when headlights or side lights are switched on, the driving lights-daytime running lights go off automatically. DRLs must be bright enough to ensure they can be seen clearly in the daytime. Their job is to improve the visibility of a vehicle to other drivers, pedestrians and the other road users. This is good for improving the driving safety, road safety.
 DRLs bring safer driving and they consume just 25-30% of the energy needed to power conventional dipped headlights. For your daytime road safety, why not to take them on your cars!
 

Reference:
*The performance requirements for daytime running lights are defined in UN ECE Regulation 87: Daytime running lights
 
*The operating requirements for daytime running lights are defined in UN ECE Regulation 48: Installation of lighting and light-signaling devices