Why Do LED Daytime Running Lights Flicker?

Cars nowadays come stocked with a bunch of various lights on the exterior. Taillights, headlights, rear lights… you’d think these light names belong on an ox rather than a car!

Certain lights are required by law to be on every car, such as dipped headlights. Others are there for optional added security or aesthetics, such as daytime running lights or DRLs.

Sometimes a bulb can serve more than two purposes by interchanging its power consumption.

Car owners may find themselves with an opportunity to upgrade their DRLs. But unless they are careful and informed about the process, they may end up with an unpleasant result.

And what could be more unpleasant than flickering lights, when all that was wanted were sleek modern, bright white LEDs. Read ahead and take notes to find yourself with a job well done.

Installing LED DRLs leads to flickering headlights and dashboard errors. This is because LEDs draw very little power compared to halogens and car computer systems are designed to recognize stock halogen bulbs. To fix LEDs flickering, install special CANBus adapters, voltage boosters or resistors.

The Main Differences Between DRL And LED Headlights

Let’s have a look at two exterior car lights and their overlapping nature in this section: the car’s high-beams and the daytime running lights.

The car’s high-beams are meant to serve an essential function. They are the brightest source of illumination for your vehicle on dark rural roads and open highways.

They are directional, pointing out from the front of the car and lighting up to 350 feet (107 meters) ahead of your vehicle. That’s about the distance between three street lights.

On the other hand, DRLs provide a vital safety function. When on, they make the car prominent to surrounding cars, people, and perhaps animals too.

They may or may not turn off when the main headlights turn on. Some manufacturers choose to turn off the DRLs when the car engine is on, but the gear is in ‘Park.’

So if you are driving a car in the daytime and the high-beam is off, the DRLs will automatically turn on, especially if it’s a relatively new car.

Since the role of DRLs is to simply indicate your car’s presence, they are not as bright as the headlights.

In cars a decade or two ago, the DRLs were not separate bulbs. The high beam bulb would operate at reduced power to serve as the DRLs.

More recently, you can see distinct DRLs are now the defining feature of newer models of cars. They are the unique gem that adds to the crowning glory: car headlights, making car owners weak at their knees! Think of Audi headlights.

Updated DRLs are housed within the front headlights but with their own LED bulbs and socket. They look sleek and very glamorous.

But let’s go back to the earlier DRLs that combined with the high beam. A lot more car owners are upgrading these stock two-in-one halogen bulbs to brighter and whiter LED bulbs.

The correct term for these bulbs is H15, where H stands for headlights.

Sometimes, swapping these bulbs for new ones leads to a number of problems, the most common one being flickering.

What Makes an Aftermarket LED DRL Flicker?

Once you’ve purchased and plugged in your new DRL/Hi-beam kit, and you turn it on, you might find that it is flicker.

When the LED bulb is in DRL mode, it appears to flicker quickly, as if it is rapidly turning on and off. Actually, that’s what causes LEDs to flicker: turning on and off. But at a lower frequency, which the human eye starts to notice and be annoyed by.

Flickering headlights used to be a more common problem, which is now being addressed by car and bulb manufacturers. But it still happens.

The core reason is the difference in technology of the stock halogen bulbs that car systems recognize and the new after-market LED bulbs.

Due to this difference, a few things start posing problems with the functioning of the light.

Remember, the hi-beam and DRL are the same bulbs, which operate at different levels of brightness. When the light switch is toggled to hi-beam, the bulb works as it should.

But when the hi-beam is turned off and DRLs turn on automatically, the bulbs start flickering.

Traditionally, cars come stocked with halogen bulbs. A hi-beam halogen bulb requires at least 55 Watts of power to output the bright long-range light.

But when you install an LED H15 bulb, for example, on DRL mode, they require only about 5-10 Watts of power!

This considerable discrepancy in power input leads to a communication failure between the car’s computer system and the LED’s circuit. The system assumes there is nothing plugged in, or it’s not plugged incorrectly.

Similarly, another issue is when the voltage is mismatched. By default, DRL LEDs use a lower voltage compared to the full voltage high-beams.

When in hi-beam, the bulbs get the full 12 V and operate normally.

When in DRL mode, they will likely flicker as they draw only about 6 Volts due to the voltage reduction.

This, too, causes the error to be generated and causes flickering of the DRLs.

The car’s CANBus control system that might not recognize the new LED correctly and return errors. Along with flickering, you may also see dashboard errors, malfunctions or radio interference.

Also read: When Should Dipped Headlights Be Used?

How To Fix Flickering Day Running Lights?

But don’t worry, I’m going to help you get some sweet LEDs onto your car and make sure they work. Several potential solutions are depending on what is causing the issue.

One solution can be found in going for a special decoder that can be installed. The CANBus adapter will effectively decode your LED DRL lights correctly to the control system. This bypass should eliminate the issue of flickering due to failed communication.

The best solution is to install a relay harness for the DRLs to work normally without flickering to fix the voltage issue. They are also called voltage boosters and maintain between 8 V to 12 V output.

They work by keeping the DRLs getting a steady power supply and voltage by simply connecting to the bulb.

Here’s another pretty cheap solution: installing a resistor alongside the LED. A resistor stabilizes the headlight’s current flow, reducing the current that flows from the battery into the LED.

The car effectively thinks it is running an OEM bulb and operates as expected, without flickering. In reality, the resistor is taking off that extra current, converting it into heat, and dissipating it.

The LED still only gets the power it is supposed to, i.e., between 5-20 Watts, depending on the bulb.

One of the better solutions to avoid potential flickering and errors is to always get high quality H15 LED DRL conversion kits.

These are retrofitted and have built-in resistors and all decoders for flawless operation. They are compatible with most cars, but just avoid any hassle with returns, check with the retailer.

Also don’t forget to read my other article about flickering signal lights, which I am sure you will find insightful.

Final Words

So now you know how DRLs and headlights share a bulb to perform two functions. It’s a great idea to upgrade the look of your car by installing cooler LEDs.

Equip yourself with these handy solutions to avoid any flickering and errors.

Have you installed DRL LEDs on your car?

How are you planning to resolve the issue?

Share your ideas with me in the comments below.