LEDs in the automotive sector

From the principle to CANBus operation

An LED (Light Emitting Diode) is a semiconductor that emits light when a current flows through it in the correct direction. The light is produced by the recombination of electrons and holes in the semiconductor - this is known as electroluminescence.

In simple terms, an LED is made up of two layers of semiconductor. One layer has an excess of electrons, while the other layer has a deficiency of electrons, or so-called holes. When a voltage is applied to the LED, the electrons from the first layer jump to the second layer and when they meet a hole they combine with it, resulting in the release of energy in the form of a photon, i.e. light. This is the phenomenon of electroluminescence.

Currently, one of the most interesting and advanced solutions used in LED retrofits are chips made using CSP technology. CSP is an abbreviation for Chip Scale Package - it stands for a LED whose size almost corresponds to the light chip itself. This makes the LED extremely small and lightweight. Why CSP and not, for example, SMD (Surface Mounted Device) or COB (Chip on Board)?

The answer is relatively simple: CSP is a modern, ultra-compact technology that combines high efficiency, space saving and reliability. It is these features that give it the edge over other solutions.

Despite its very small size, it can shine very brightly (e.g. with the CSP LED 1860, a luminous flux of up to 1800 lumens can be achieved). It allows a wide angle of illumination, as well as thanks to its design (there is no plastic casing to damage - this makes the diode more resistant to shocks and long-term operation). In addition, the CSP is distinguished by its special design, where the chip is connected directly to the anode and cathode, so that the current spreads evenly through the structure. This allows better heat dissipation and increases thermal resistance, and by using a thin layer of luminophore, we obtain light that is uniform and has no discolouration.

What is the difference between light from an LED and light from an incandescent bulb?

LED light differs from light from a traditional incandescent bulb in basically everything. Let’s start with the way the light output is created. In a traditional incandescent bulb, light is created by heating a thin wire (tungsten filament) to a very high temperature (around 2000-3000°C). In an LED (light emitting diode) bulb, the light output is produced by the phenomenon of electroluminescence - the flowing current causes the semiconductor to glow without the need for high temperatures.

The second thing to look at is energy efficiency. A traditional incandescent bulb has a very low efficiency, which is mainly due to the fact that most of the energy consumed is converted into heat rather than light. LEDs, on the other hand, are much more energy-efficient, using less energy for the same amount of light.

Another feature that differentiates a standard incandescent bulb from an LED bulb is the lifetime. In this case, it is worth noting that the difference is enormous. The lifespan of a traditional halogen light source is usually estimated to be between 300 - 600 hours, while that of an LED is between 3000 - 30000 hours.

A noticeable difference between the light of a halogen bulb and an LED is the colour temperature, commonly referred to as the colour of the light. Traditional incandescent bulbs have a yellowish light colour and their colour temperature fluctuates around 3000 Kelvin. LED light can have any colour of light from very warm (2000K) to very cold (6500K) depending on the application.

At this point, it is worth mentioning ecology, a very fashionable topic in recent times. In this context, LED solutions are more environmentally friendly, as they use less energy and leave less waste after use.

What is CAN bus and how does it work - what is its role in the CAN network?

The CAN bus is, in short, a scanner for the vehicle’s installation. It was developed by Bosch in the 1980s to enable communication between different electronic modules without the need for a central computer. Its main task is to search for faults and check the correct functioning of the various components of the installation in real time.

CAN bus (Controller Area Network bus) is an advanced network communication system used in automotive applications that allows data to be exchanged between different electronic modules in a vehicle without the need for a central computer. Its main advantage is that it allows direct communication between multiple controllers (ECUs - Electronic Control Units), which means that each module can send and receive data using it. In this way, CAN bus allows a reduction in cabling because, instead of running separate wires to each module, a single bus wire can handle multiple signals. Additional advantages are also speed and reliability (it is a system that is immune to electromagnetic interference and can operate in harsh environments, as well as providing fast data transfer, which is crucial for the operation of modern vehicle systems).

Its main applications in the automotive field are the engine and powertrain (e.g. engine and gearbox control modules), safety systems (e.g. ABS, ESP or traction control system) and the possibility of comprehensive vehicle diagnostics.

Interaction with CAN installation?

LED retrofits in the context of automotive lighting are often confronted with problems of interoperability with CAN bus installations. There are two main problems with the compatibility of retrofits with CAN bus. The first is their low power consumption compared to traditional halogen bulbs which can be interpreted as a faulty or missing bulb. This results in an error display on the dashboard which can be annoying for the driver. The second is the malfunctioning of the lighting system after the LED retrofit has been fitted, which in some cases can result in flickering or malfunctioning lights (the CAN bus system is unable to correctly recognise LEDs as a suitable light source). Cars with a CAN bus system often monitor and control all components, including lighting, and if the LED retrofit is not compatible, the system may display errors.

What about other light bulbs?

Retrofits are not just replacements for bulbs in dipped and high beam headlights. Are there issues with other bulbs too? To begin with, it is worth clarifying what retrofit actually means. In automotive terms, retrofit refers to the modernisation or retrofitting of a vehicle with new technologies that were not available at the time of manufacture. It is about making technical changes to an existing vehicle so that it meets new requirements, standards or offers new functions.

In the context of lighting itself, retrofit refers to the modernisation of existing luminaires by replacing the light source (e.g. bulb) with a more modern and energy-efficient one - most often LED - without having to replace the entire luminaire.

In automotive terms, the word retrofit is most often associated with headlamps, i.e. dipped or high beam headlamps. However, the term is much broader and applies to all bulbs that we can find in any car, both inside and outside the vehicle.

The problems associated with LED retrofits are not limited to dipped or high beam headlights - they also affect other bulbs in the car, especially where the electrical installation is controlled by the CAN bus system (the most common applies to exterior lighting). The problems associated with changing to LED lighting manifest themselves differently depending on the function performed in the car’s exterior lighting. Thus, in the case of turn signals and the replacement of a traditional bulb with a retrofit, the main and most frequent problem is that the so-called hyperflash flashes too quickly. Often, a burnt-out bulb message can also appear on the dashboard. A similar error is also possible with regard to the parking/position lamps (additionally, the retrofit may blink when switched on), the number plate light as well as the stop lamps.  In addition, in the latter case we may encounter the absence of a burnt-out bulb warning. Under normal circumstances, if one stop bulb burns out, the computer should warn the driver. However, if one of the bulbs used is a retrofit LED and the other a halogen - the system may not detect the problem at all. In the case of reversing lights, in addition to the already mentioned message display on the dashboard, there may also be interference problems with the reversing camera (LED generates electromagnetic noise).

The situation is quite different in the context of vehicle interior lighting, such as the headliner or gloveboxes. In this case, the use of retrofits is much less disruptive in terms of the problems encountered. This is due to the fact that the interior lighting of a vehicle is usually not connected to a bulb monitoring system, so its failure does not cause a burnt-out bulb error on the dashboard (exceptions may be modern or luxury vehicles).