Automotive Lighting : Reconciling Engineering and Design

I had the pleasure to interview Mr Nelson Faria, owner of Wavelength Consulting ltd. His company specializes in Research, Design and Development of lighting systems. The business caters from feasibility studies of ideas, authoring engineering requirements, project management, CAD/CAS, CAE (including Ray Tracing) Rapid Prototyping and benchmarking. We naturally connected as A2MAC1 covers Lighting systems and is expanding its activities in the field of Lighting & ADAS costing.

Enjoy the reading !

Automotive lighting went a long way and seems to accelerate its pace of innovation. What motives such rapid changes ?

The automotive industry is going through a transformation period. On one hand, more stringent emissions regulations regarding ICE-powered vehicles risking high fines if not meeting legal targets, on the other, the need to ramp up the development and manufacturing of EVs able to achieve a range and cost comparable to ICEs. In both cases, the OEMs find the need to increase their vehicles' efficiency to meet stricter emissions regulations and improve EV's range while maintaining the business profitable. More than ever, manufacturers are under immense strain.

The introduction of LED technology promised lower power consumption, much longer life, performance improvement, and an ultimately higher degree of design freedom never seen before.

This technology allowed us to move from the simple and ubiquitous circular apertures and large reflectors typically used by incandescent light sources in favour of a more multi-form design. This approach enabled the ability of "slicing" the illumination and signalling functions into smaller portions (Matrix arrangement of LEDs) and the use of polymer-based optical elements closer to the source as a result of negligible IR emission.

How does it impact the design language of modern cars, both interior and exterior ?

The automotive industry's future will be mainly electric-powered, involving a degree of autonomous driving, and increased environmental, safety, and ethical questions. Consequently, the industry will be focusing on the origins of the raw materials they buy, efficiency, range, cost, and user experience as never before. Inevitably these regulations and ideals influence the design language of their products.

The interior design of several premium models already on sale are good examples of the above trends, from vegan interiors, seats made of recycled PET bottles, textiles, and artificial leather. You may have also noticed the gradual replacement of physical buttons by touchable surfaces and minimization of functions, for instance, smaller visible optical illumination/signalling apertures and hide functions behind porous materials that only reveal their functionality when required, otherwise staying inconspicuous when not in use.

This aesthetic aims to emphasize the purity of the form, reinforcing the user perception of efficiency and effortless user experience (debatable UX). The current exterior design language predominating on the market is what some people may call "fussy" or "over-styled", made of over creased and over detailed surfaces.

However, some manufacturers are evolving the exterior design language to match the interior orientation of minimalism. A good example is the Range Rover Sport vs the Range Rover Velar. You can easily observe that on both models exterior design languages reflect their interiors. The Velar exterior is sculptural and clean, lacking dramatic "creases" and the flush door handles enhance that feeling.

How does it affect the design of lighting systems ?

"The minimization of body optical apertures destined for illumination and signalling functions poses a significant challenge in designing efficient lighting systems that meet an acceptable compromise between Design, Engineering and Financial requirements."

This new visual approach has a significant impact in the exterior lighting system, favoring slender body apertures with a dramatic shortening of the overall lamps cluster height. The lamps interior visual surfaces are cleaner and simpler shapes aiming to make the lighting functions more inconspicuous.

These design ideas aren't new when discussing the evolution of exterior body design. You can go back as far as the early 30's of the previous century to find examples of such design language, in the form of the Cord 812 and Talbot-Lago for instance. Since then the desire of concealing or making inconspicuous illumination and signalling functions has been pursued along the decades in one way or another until the 90's when the pop-up headlights ceased due to aero and safety concerns.

A significant approach being pursued by some OEMs, is what I call the "camouflage" approach. This approach aims to conceal the lighting functions through blending the exterior shape and interior surfaces colors with the surrounding trim, BIW shape and colors. By disguising the lighting functions to look like a piece of body trim when not in use and finally the divert approach where the designer aims to conceal the lighting functions by drawing the attention of the observer away from the function.

Such design ideas would be easier to implement by making the optical exitance apertures as small as possible. In stark contrast to the interior lighting systems, the exterior illumination and signalling make use of substantial higher power to operate to meet the legal requirements and acceptable safety performance levels in contrast to the interior lighting functions.

As such, the minimization of body optical apertures destined for illumination and signalling functions poses a significant challenge in designing efficient lighting systems that meet an acceptable compromise between Design, Engineering and Financial requirements.

Visual product identity, electrification, automated driving... how do all of that translate when designing a lighting system? What are your main challenges?

"A typical hurdle in Lighting is to strike a consensus between Design needs and what the current technology can offer within vehicle program budgets."

As a result of the latest stringent environmental regulations in Europe, the automakers are under pressure to reduce their fleet average CO2 emissions (<95gCO2/Km) otherwise they could risk the payment of significant fines for every gram over the threshold. One of the strategies to reduce the average emissions is to increase the availability of EVs within their fleets.

Currently, the costs of manufacturing EVs are still higher than ICE counterparts, mainly due to the battery. It has led to a higher price of entry of ownership that combined with range anxiety experienced by a fraction of the population, constitutes a key barrier to greater market penetration. One of the most cost-effective ways to reduce the cost per vehicle is to maximize the efficiency of the entire vehicle systems and Lighting isn't an exception.

A typical hurdle in Lighting is to strike a consensus between Design needs and what the current technology can offer within vehicle program budgets. The push to reduce the optical apertures further and still achieve acceptable efficiencies are challenging the limits of current light sources. The optical aperture of a given system is governed by the size of the geometric extent of the source, also known by the French term, "étendue". For the highest collection efficiency to be possible, the source is required to emit within the acceptance/collimation angle of the optical system e.g. the smaller the optical exitance gets, combined with narrower collimation angle, inadvertently leads to lower efficiency.

Are there technical solutions to resolve this dilemma ?

The current solution is to add more powerful LEDs at the expense of optical efficiency, leading into increased energy consumption, higher cooling requirements, increased mass and ultimately higher costs. To achieve smaller exitance, we need to develop newer broadband sources that can produce higher luminance within a significantly lower-emitting area with lower spatial divergence of the emitting radiation, all under an acceptable automotive cost.

The closest competitor to the LED technology is the so-called "LASER light” name coined by BMW and AUDI. Even so, such a designation could allude to ideas of Star Wars laser beam style; you may be disappointed to know it's not the case. In essence, it works like a typical white LED, except the phosphor is activated remotely using a collimated blue LASER diode, reducing the emitting area and increasing brightness levels in the process.

The most significant advantage of this technology is that it allows decoupling of the actual optical system that forms the beam shape from the source, enabling to be powered remotely through a glass optical fiber, GOF. However it's still a costly system.

"The collaboration with A2MAC1 gave us the opportunity to have an insight into the exterior Lighting of two premium vehicles."

The collaboration with A2MAC1 gave us the opportunity to have an insight into the exterior Lighting of two premium vehicles, Audi A8 and Audi e-tron, both are defined by their powertrains, ICE and Electric respectively. The two models are ECE based, LED matrix, and both are equipped with ADB functionality (Adaptive Driving Beam).

To have a sense of the technical progress made in the last few years, the Alfa Romeo Giulia will be used as a baseline as it makes use of a combination of incandescents and solid state light sources for illumination and signalling functions e.g. HID system and LEDs.

The A8, being the company flagship, comes with some extra refinements the e-tron doesn't possess such as auxiliary High Beam (remote phosphor activated by laser) and significantly higher horizontal angular resolution. This resolution difference can be easily observable by the beam projection on the wall. Being the technological "tour de force", the tail functions are OLED based. In comparison, e-tron and the Giulia make do with LEDs for tail functions.

Shall we compare the design execution of the lighting systems of the Alfa Romeo Giulia, and the two Audi A8 and e-tron ?

Sure ! First, let's decompose them.

Now, let's compare the mass, the amount of parts and the power using the Alfa Romeo Giulia as our "0.0" baseline.

The Audi A8 system seems complex and very heavy. Any thoughts?

The A8 complexity doesn't stop with the visually busy appearance; it goes deeper. A good example of that complexity is the chosen engineering design of the DRL, DI and position combined functions. It's made of 90 LEDs in total, powering a combination of light guides and light “blades” covered by a diffuser element. This very complex arrangement is potentially chosen to achieve a highly uniform signature (DRL/DI and Position) at the expense of efficiency. As a consequence of this complexity, it isn't surprising that the A8 BoM dwarfs by considerable margin both the e-tron and the Giulia. Not surprisingly it's the heaviest of the lot!

The A8 Low Beam function is formed by an array of 3 modules, each having an aperture height of considerably lower than the others in this comparison. It's approx. 42% less than the height of the e-tron and easily shorter than the Giulia. Due to this significant difference in optical aperture height, it's likely the Low Beam function to operate in a significantly less efficient manner than either e-tron or the Giulia. The Low Beam of the A8 the optics are made of glass sustains our suspicion that the system isn’t very efficient.

How do the extra mass and power consumption of the lighting functions have any impact on the EV range?

"What is surprising is the difference between the Giulia lamp and the Audi e-tron lamp, even so, the later beats the Alfa Romeo by smaller margins."

To have a better sense of the impact of these forwarding lighting lamp clusters, key characteristics, mass and power consumption, may have on EV's range, we can create a hypothetical case. The estimation of the EV range will be based on the WLTC, Worldwide Harmonised Light Vehicles Test cycle, not only day time driving [WLTC default] but as well estimate the range if driven at night. The full Worldwide Harmonised Light Vehicles Test Procedure, WLTPC, can be found here.

Note:

• For this exercise we will not consider the tail functions.
• The Giulia being the lightest and making use of the HID system will be used as a comparison baseline.
• To make the comparison fairer, we will assume the ADB based lamps mainly use the Low Beam 60% of the time.

For the range estimation, the hypothetical EV range will be base on a battery pack of 94kWh going through the WLTC Class 3b driving cycle (+ 450 Watts in total for other electric devices, power windows, radio, seats etc). Other EV key characteristics are the following:

In both cases, the daytime and nighttime drive as a whole, they achieve an average range of 473.64 km and 470.17 km respectively. What is surprising is the difference between the Giulia lamp and the e-tron lamp, even so, the later beats the Alfa Romeo by smaller margins. The largest difference occurs at night time of approximately 1km for the e-tron. The most significant difference occurs between the e-tron and the A8, for both cases, daytime, 1.5 km, and night time, 2.38 km. The difference may appear very small, but that could be the difference of reaching a charging point or not.

This result may surprise some folks which would be expecting the biggest gap to occur between the Giulia lamp and one of the LED-based lamps.

In short to mid-term future, the ADB functionality is likely to gain further acceptance by the public. It is reasonable to assume a significant shift towards the High Beam usage combined with a more sophisticated system; it's likely to increase the use of the High Beam than the assumption that was made for this case.

However, if the trend of reducing the optical exitance trend continues without a significant light source improvement (high power light source with a considerably smaller geometric extent at an affordable cost) could mean even higher power consumption in future systems.

The increased usage of high beams may aggravate the matter further.

At first glance, the mass appears not to matter. Why is that?

"Design optimisation of all the vehicle systems has always been important, but now more than ever."

The reason why the mass appears not to penalize the estimation of the vehicle range relies heavily on the fact the WLTC cycle is biased to low speed and start-stop situations typically found in city driving. The WLTC cycle is only 30 minutes, and a good portion is made off by the low-speed phase (see graph) with a very significant amount of time standing still. Hence it is not so surprising the outcome of the test.

Nonetheless, it can be observed the impact of carrying excessive mass may have on the overall EV range. The chart shows approximately that for every extra kilogram added, penalises the range by about 0.04 Wh/km.

To have a better sense of the impact of the lamps mass (for that matter any vehicle system mass) on the vehicle energy consumption, we can delineate a case where the vehicle would be travelling on the motorway for a significant period of time. In my not-so-distant past, I used to commute 80 km each way to one of my previous employers. A commute route mainly made of motorway driving taking approximately 45 minutes.

We can use the WLTC extra high-velocity phase as a reference to estimate the average energy required to carry the lamp's mass along the motorway commute.

The outcome shouldn't be to anyone's surprise; the heavier the lamps and higher sustained speeds higher the energy consumption. Another aspect not mentioned here but of great importance are the effects the mass has on the vehicle dynamics and handling. The heavier the vehicle, the harder it is to accelerate, stop and go around corners. Due to the nature of the current battery technology, it's not uncommon to find saloons weighing more than 2 Tonnes! Until recently most of the vehicles weighing that much would be luxury SUVs.

Vehicles such as the Porsche Taycan Turbo S and Tesla Model S long range with batteries packs of similar capacity are over 2 Tonnes. By norm EV are heavier than their ICE counterparts of similar class and range. To carry this extra bulk, as a result of the batteries, a more robust suspension and brakes may be needed leading to additional costs.

Hence design optimization of all the vehicle systems has always been important, but now more than ever. From the smallest to the largest system, all come together to form a vehicle. Lighting systems aren't exempt, and ensuring the engineering design of the lamp is as effective as possible is essential. Such an approach is required to ensure the vehicle as a whole stays competitive within its class.

Improving efficiency is the key but you cannot switch mass when not in use... What else can be improved?

Reduction of optical apertures leads to lower optical efficiency, increased electric power, cooling requirements and mass, leading to higher energy consumption. If we wish to improve the current efficiency levels, we will require to develop new types of broadband light sources with significantly lower etendue than current LED technology can offer.

Meanwhile, there is still room for optimisation of the lighting systems. The "new" design trend of minimalism (smaller optical apertures), at the same time, may provide the opportunity for reduction of optical surfaces (e.g. DRL, DI, Pos), the number of parts (e.g. bezels, screws, and optics).

To conclude, any thoughts on how autonomous driving will impact the current exterior lighting systems?

"Exterior lighting technologies may go towards remote sensing, entertainment, and communication."

Dramatically! The move towards autonomous driving would mean the vehicle would rely far less on the driver's inputs. Shifting the exterior illumination and signalling systems to perform the minimum requirements by law, since exterior lighting functions may only be expected to be used on a limited basis, more akin to a backup system.

This move could reveal to be an opportunity, in making it easier to implement the minimalist aesthetic some OEMs are pursuing e.g. Polestar concept Precept.

As we get closer to seeing autonomous vehicles on our streets, the interior lighting systems will gain even further attention and emphasis will be on User Experience. Some of the future advancements in exterior lighting technologies may go towards remote sensing, entertainment, and communication e.g.:

• Surface identification, multi/hyper-spectral technologies.
• Projection of greeting messages/animations on the ground and alerts to warn pedestrians the vehicle is engaged in autonomous mode V2P.
• Payment of the motorway toll and passing vital information to other vehicles V2I & V2V.

Thank you Mr Nelson Faria, Wavelength Consulting:

• Website: www.wavelength-consulting.com
• Email: info@wavelength-consulting.com
• LinkedIn page: https://www.dhirubhai.net/in/nelson-f-ba72432b
• Phone number: +44(0)7922 813924

A2Mac1 services Lighting Analysis, AutoReverse, AutoVision, MediaPack were used to realize this study and illustrate this article. A special Thank You goes to Matthieu Blary, Lighting Analysis, European Manager, and his team without whom this article would not have been possible.

Glossary :

• ADB - Adaptive Driving Beam
• DRL - Daytime Running Light
• DI - Direction Indicator
• HID - High Intensity Discharge
• HB - High Beam
• LB - Low Beam
• Pos - Position Light
• WLTC - Worldwide Harmonised Light Vehicles Test cycle
• WLTPC - Worldwide Harmonised Light Vehicles Test Procedure.