Most vehicles come manufactured with a a lower voltage mode set in their headlights to be used as daytime running lights (DRL). However, if you are using OEM or aftermarket HID/LED headlight bulbs, this can lead to significant issues.
Daytime Running Lights (DRL) are designed as a safety feature for daytime driving, enhancing the visibility of your vehicle to other drivers. DRLs are designed to use your headlight bulbs in a dimmer mode, employing various methods to achieve this. By dimming the original halogen bulbs, DRLs contribute to increased safety on the road.
Resistance Dimming. If your vehicle, like many Subaru models, has a resistance Daytime Running Light (DRL), you can often disconnect the DRL resistor module to fully bypass the DRL system.
PWM Dimming. If your vehicle utilizes a PWM circuit to dim the lights for the DRL function, it indicates that it rapidly fluctuates the voltage to the light bulb circuit. This causes the halogen bulb to dim, yet the flashes occur too swiftly to be perceptible by the human eye. To address this specific issue with DRL, a PWM module is implemented as a solution.
Low Voltage Dimming. If your vehicle is designed to step down the voltage from 12V DC to a lower voltage, LED Bulbs would be your choice because they are designed to function at these levels.