Vertical Illumination

Dipl. Designer Wilfried KURZ, MLL, Bartenbach Research & Development, Austria

The order of the day, in everyday life, is not to think about walls and their relevance. Walls are useful for hanging clocks, mirrors, TVs and pictures. The things that we want to look at can be highlighted and give the room a recognizable identity. But the basic function of a wall, as part of the architecture, is to create an artificial space by separating the outside from the inside. This can now be conditioned with temperature, humidity, acoustics and brightness to create comfort. We then select a wall color, wallpaper or textured wall covering, or opt for exposed concrete. This combines the visual identity with the sensation of the space and creates another type of comfort as the basis of visual perception, as we will see.

In consequence, two different types of lighting concepts are meaningful. Conventional point-shaped spotlights with rotationally symmetrical light distribution create parabolic figurations on walls. Traditionally, (halogen) incandescent bulbs in various designs or high-pressure discharge lamps served as light sources; linear lighting systems were implemented with fluorescent tubes to generate large bright surfaces. Nowadays, the advantages of spectral quality and efficiency of conventional light sources have long since ceased to be a categorical decision in the planning process. With the use of LEDs, they have become precisely plannable and targeted properties.

The replacement of conventional light sources with the LED, has not only changed lighting technology, but also created opportunities for how to work with artificial light. Technical freedoms allow a strong focus on architectural qualities and the light source integrates itself much more into the architecture. The luminaire becomes more and more invisible, but still perfectly illuminates the wall or the object on the wall. The basic lighting tasks remain the same, whether it is something on the wall, like a painting, or the wall itself. We usually don’t focus on the wall itself, so the relevance in perception of space defining vertical illumination is briefly shown (Figure 1) [1].

Figure 1: Three types of vertical brightness highlighting accentuating, wall-related planar and self-luminous.

Perception of Contrast

The example images of the displayed painting were taken in automatic mode, and for the best result we would adjust the exposure parameters (Figure 2). Perception works similarly, adapting the visual process to the focused task. At a physiological starting point of this, the contrast sensitivity (a basic visual function) is optimal if the focused task (center luminance) has a higher luminance than the ambient field (Figure 3) [1].

Figure 4 shows different perceptions of a room: the lighting situation does not change. The remission (spectral reflectance) of the walls defines the white balance, while the surface structure adds information. Bartenbach completed extensive studies on ambient effects and there is a significant increase (or decrease) of wellbeing and performance with choosing a (non) matching surface (Figure 4).

The Perfect Wallwasher

A wall that appears homogeneous is not evenly illuminated over its total height. Studies for museum lighting showed a three times brighter upper area (Figure 6). If the ratio is above this, the wall appears unnaturally flat, like a wall of fog. Down to an approximate ratio of 10 to 1, the wall is perceived as fully illuminated. Below that, the upper part starts to dominate. Lighting at 30◦ to the vertical creates an optimal modelling effect for exhibits. Wallwashing can be somewhat steeper, but the light distribution must be designed for this (Figure 6).

Figure 2: The lighting level of the visual task and the wall is constant. Only the different degrees of reflection of the wall lead to different contrast ratios and perceptual qualities.

Figure 3: The contrast sensitivity is optimal if the center luminance is higher than the ambient one (stable perception) [1].

Figure 4: Colored and structured walls prime our perception in a subliminal way.

The closer the luminaire is to the wall, the longer the shadows will be. The quality of the wall plays an important role. Unsightly waves of the hastily constructed cast-inplace concrete shell quickly become visible, much to the displeasure of the client and architect. However, if the visible effects are desired and the wall is provided with an appropriately structured surface, wallgrazers are used. Their optics are designed to sweep across the wall at a very shallow angle, creating a high-contrast, three-dimensional relief (Figure 7).

Figure 7: Wallgrazers model particularly plastic.

Unfortunately, diffuse accent lines for main lighting are often oversized at this ceiling position close to the wall and then form a glaring light channel without architectural qualities. The upper part of the wall has an important role to play. A formally aesthetic interplay of light, luminaire and architecture is desired. Besides a minimized appearance of the luminaires, the wall should be illuminated up to the upper edge, no light traces should appear on the ceiling. For this purpose, the lighting technology must be completely installed in the ceiling. Protruding parts create undesirable halos due to scattered light. The planning properties described so far can, in principle, be achieved using linear optics, but these can only direct the light precisely in the transverse direction to the wall. For light-directing properties in the longitudinal direction, individual optics are assigned to each LED. This point light source also controls the radiation in the longitudinal

Figure 5: (top) The Semper Gallery in Dresden features balanced contrast and color to achieve the desired perception. (bottom) The Staatsgalerie in Stuttgart changes the perception of space through different brightnesses, contrasts and colors.

Figure 6: (left, right) Perceptual studies for visually uniform illumination of walls indicate a luminance ratio of three to one. (middle) The wall is illuminated with a wallwasher placed too close. A wallgrazer offers optimized light distribution for such applications.

direction, which, for example, allows for radiation limitation in order to avoid glare.

Modeling has a visibly better quality, since longitudinal shadows are now also created. The end of a wall can be defined more precisely. Glare is prevented in the longitudinal direction, so it is useful for all walls with open ends, such as corners, that allow a view into the lighting system when passing by. To allow point light sources to blend smoothly into each other, the light distribution needs a soft but defined edge. This is also an advantage for lighting design because the luminaire spacing becomes variable.

Wall and More

Precise light directing and glare control are determined not only by the reflector geometry, but also by a patented micro-faceted surface consisting of complex free-form surfaces that superimpose the desired light distribution several times. This ensures optimum color mixing for any dynamic color applications such as Tunable White or RGBW. Furthermore, it enables application concepts that go beyond immediate spatial allocation. Two examples are given below.

For a smooth transition from a horizontal to our vertical illumination, the distribution of a downlight and a wallwasher can be combined. This optic, called Downwall, is ideal for general lighting of corridors and rooms (Figure 8).

Figure 8: The adjacent downlights are switched off to visualize the mode of action.

With high luminous fluxes from COB sizes of up to 15mm from the large version, multi-story wall heights can be illuminated

Figure 9: (top) Downwall reflectors are available with diameters of 80, 40 and 13 mm. (middle) Pinhole downlight and downwall with 13mm visible diameter. (bottom) The store as a stage. Visual comfort while buying goods, brilliant light without the usual glare of too many spots.

while the small version can be combined with a pinhole downlight in the same 13 mm diameter for a sophisticated interior design (Figure 9).

Furthermore, excellent shelf spotlights can be realized, which are mounted directly under the usually high ceiling and then illuminate only shelf areas including adjacent visual tasks. This approach is reminiscent of stage lighting, and the theatrical characteristics create a focused and high-quality environment (Figure 9). Stage lighting designers, themselves, also appreciate this perfect light control for planar light in high precision (Figure 10, Figure 11).

Figure 11: Two times four LED spectra in red, green, blue and royal blue, respectively cyan, amber, 2200K and 6500K - the Dalis Cyclight creates high intensities in a wide variety of pastel and saturated colors.

The Personal Wall

Modern optics master the milieu-defining property of glare limitation to a high degree. Using light only where it is needed creates spaces with a high quality of perception and thus of stay. Vertical surfaces are in the visual focus of people and determine spatial qualities even more than the ceiling.

Figure 12: The rear panel of the Personal Table Light (PTL) serves acoustic and biological purposes. Figure 10: Smooth transitions and soft fades for high-quality color dynamic backgrounds on stages and studios.

This becomes clear in the open-plan office. Room-in-room concepts replace missing walls and create spatial structure and functionality. But just as with the furniture or acoustic concept, a coherent lighting concept is needed that is oriented to the visual, biological and emotional needs of people in order to create a consistent activity-supporting milieu. Visual activities can be solved by assigning a luminaire to a visual task. For biologically effective brightness, light and surfaces have to interact.

Figure 13: Room-in-Room system.

In order to maintain the positive aspects of an open-plan office, such as mobility and flexibility, and to use them profitably, the acoustically effective divider at the desk was used as an instrument for the lighting design in the EU project Repro-Light [2,3]. The Personal Table Light (PTL) [4,5] is a lighting solution for visual and biological light, which can be controlled separately and personalized by the user themself (Figure 12). The high biological brightness for a light shower is realized in a white mode as well as in a 490 nm cyan mode. The extensive studies show an increase in user well-being and performance.

The principle was also applied to a roomin-room system [6]. Precise light distributions and optimal glare control enable a variety of usage scenarios and a light shower for biological activation on 2 m2 (Figure 13). The approach results in qualitatively coherent lighting concepts with room and workplace specific luminaires that can not only combine the aforementioned flexibility with standards and energy requirements, but also represent a gain in spatial integration.

The Technological Wall

The tool to selectively illuminate wall surfaces is now the basis for further improvement. The limiting factor is now the wall itself, whose usual colored paint scatters the incident light back into a diffuse soup. A decorative texture increases the wall’s appearance, but not the quality of light. This can be improved, and various approaches have been developed over time. A wall can be provided with a photometric surface for directional reflection into the room. In this way, higher vertical brightness is created and visual tasks can be illuminated in a targeted manner. The high luminance of the LEDs can give the wall a brilliant character (Figure 14).

Reflective surfaces are characterized by a more or less technical appearance, whose character should match the interior design. Another example combines lighting and visual requirements and adds a dematerializing effect that removes the perception of a room limiting wall. To achieve this, a silky matte aluminum panel is covered

Figure 14: The wall can be covered with textures that reflect the directional irradiation.

Figure 15: A reflective aluminum plate covered with a mesh-like texture.

with a mesh-like texture. Under flat viewing angles, the visual appearance is soft and white (colored versions are also available) like a normal wall; in direct view, a depth effect is created (Figure 15).

The above examples deliberately pick up on the photometric and visual properties of another type of vertical surface in rooms: the spatial openings of windows and glass fronts. These include high luminance, directional light incidence, and a space-expanding effect. Thus, we are in a class of hybrids that derive their qualities not from solid walls, but from their counterpart. In particular, the directional radiation distinguishes these solutions from similar approaches such as pixel screens or diffuse light walls. Another example simulates a window or a glass front. The way it works is simple: the light from a wallgrazer is directed towards the viewer. The prominent impression is well suited for peripheral applications in lecture halls or similar spaces. Aesthetically modified variants provide interior designers with an atmospheric tool (Figure 16).

Walls very much influence the character of a room and vertical brightness contributes significantly to the quality of stay, not only in a biological context. They are part of the subconscious base for a pleasant stay and good artificial light can also compensate for architectural deficits. Daylight is certainly the first choice, but the examples shown above are more than supplementary solutions. The advantages of artificial light and daylight can be combined to create unique solutions. These serve the demands of holistic lighting design for visual, biological and emotional qualities and their benefits for people to a high degree. ■

References

[1] SCHUMACHER, R.O. (1940): „Die Unterschiedsempfindlichkeit des helladaptierten menschlichen

Auges“. Dissertation. Technische Hochschule Berlin. [2] Repro-Light. https://www.repro- light.eu/ bzw. https://twitter.com/Reprolight. [3] Repro-light: Die Leuchte der Zukunft - nachhaltig in

Produktion und Nutzung. online : Licht2021. [4] Wirkung einer personalisierten Beleuchtung mit „Lichtdusche“. W. Pohl, baua Bericht zum 11. Symposium Licht und Gesundheit [5] Bartenbach GmbH. Personal Table Light. [Online] 2020. https://www.youtube.com/watch?v=XdYouJ sOV7U. [6] M House (xchange design GmbH).

Figure 16: The underground impression disappears through the virtual room opening.

Author: Dipl. Des. Wilfried KURZ, MLL

Wilfried KURZ graduated as a product designer and worked for a renowned lighting manufacturer in the first few years after graduation. Following that he was selfemployed with a studio for light and luminaires, where he acquired a broad and deep wealth of experience together with other professionals from art and technology. A master’s degree at the Bartenbach academy rounds out his areas of expertise. Since 2015, he has been implementing his networked thinking in the relationships between people, light, space and product in the research and development department at Bartenbach.

Bartenbach GmbH is an engineering office independent of implementing companies and deals with the conception, planning and realization of daylight and artificial lighting technology, model construction and system development of luminaires and luminous ceiling systems as well as daylight elements. Thanks to best networking in the lighting industry as well as in-house research and development department, it is possible to solve highly demanding problems in daylight and artificial lighting design. We serve lighting industry customers, research partners and clients worldwide who want to use light to generate added value in their business areas, and we work closely with architects and building owners.

Image Credits: Bartenbach, except: Contrast Sensitivity – R. O. Schumacher, Sempergalerie Dresden – Lothar Sprenger, Wallgrazer – unsplash - Mateusz Buda, Shoplighting – XAL Squadro at Oasis Store - Dan Preston Studio, Stagelighting – Robert Juliat / Dalis Cyclight, Room-inRoom – Xchange mhaus / Daniel Korb, Restaurant at Quellenhof Merano – Helmut Pierer.