Three of the four 1928 competition boards presented, at their right sides, explicit sun studies. The board with the site plan (fig. 2) shows the solar geometry at the days of summer and winter solstices and spring and fall equinoxes. For each of these days, the hourly sun positions (elevation and azimuth) were constructed within a series of circles and then combined in a table. The top left circle in each diagram (fig. 3a, here a detail for the summer solstice) represents the terrestrial sphere on which the latitude of 52º40’ (Bernau’s position) and the sun’s angle of incidence relative to the tilted Earth axis of 23º30’ are drawn. The overlaid smaller circle represents a top view of the latitude, on which the position of the north-eastern sunrise and the north-western sunset were constructed. This top view is replicated in the larger upper circle to the right, used to geometrically determine the elevation and azimuth for each single hour, which were then recorded in the table. It is surprising that the geometric derivation of the sun positions became a subject on the competition board—wouldn’t the table be sufficient? It reveals how important this topic was the architects. The juxtaposition of the solar geometries and the site plan was obviously meant to show that the building’s configuration directly resulted from the sun position analysis.

The site plan shows the individual building units develop along a line running from south-west to north-east, thus turning 45º from the cardinal directions. The diagonal placement result in south-east facing bedrooms (suggesting that guests get up with the rising sun), a south-west facing main entrance (guests are welcomed at a sun-flooded entrance in the afternoon), a gymnasium looking toward the cooler north-east direction, and all rooms oriented with respect to the point in time of their actual use (fig. 3b). This careful alignment of the rooms to the inter-cardinal directions is a theme that can be found in many student assignments at the Bauhaus after the ADGB-School competition.

The two examples of the bedrooms and the classrooms show how the Bauhaus tried to develop and also document an analytical design process. Comparing this to the calculations of the St. Peter’s School competition, Bernau’s graphical determinations look less abstract. The St. Peter’s School calculations required the readers to know concepts of diffuse daylight, illuminance, and complicated metrics. While in the ADGB-School not everybody might have comprehended the geometric construction of the solar incidences, the representation of the sun patterns on the floorplans was an image that the viewer could intuitively know from direct experience. However, it needs to be added that the geometric method has its limitation, too, because only direct solar radiation can be represented, but not indirect, diffuse daylight. The latter turned out to be the preferred lighting mode for classrooms, because, as Wittwer put it, the “diffuse (scattered) daylight is the best working light, direct solar radiation must be avoided here.”[20] As a consequence, we do not find solar analyses for the butterfly ceiling in later drawings. At the Bauhaus both analyses procedures—the calculation of illuminance for diffuse daylight and the geometric construction of direct sun radiation—continued to be studied, with a larger number of archived documents for the latter method.

The comparison of the competition and construction documentation boards show that the reconfiguration of the bedrooms and the reorientation of the classrooms, including their new ceiling form, led to an improvement of the daylight utilization. The solar studies played their part in this. Although there are no solar studies for other rooms in the ADGB-School, more changes related to daylight can be discovered between the competition and the completion phases. The auditorium, for example, was conceptualized in the competition with a “ceiling construction in ferroconcrete with glass blocks” (fig. 6). In the end, the room was built with an opaque roof and a large clerestory at the north-west façade. Annie Albers developed for this room a “rippled silver fabric,” which reflected the daylight and improved the acoustics: “Almost transparent cellophane threads, wadding-like white chenille, and thin black cotton thread were connected in various weaving intensity. The wavy, metallically shining fabric surface could purposefully direct the incidence of light, which Albers had certified by the Zeiss Ikon company. The wall-facing side with the wadding-like fabric layer had a sound-absorbing effect.”[21]

Another example is the dining hall, which had two elongated skylights in the competition drawings but was eventually completed with four stripes of glass blocks on the roof, placed at the entrance area of the dining hall. The dining hall was separated from the long access corridor by means of a transparent glass wall, and, at the other end, it opened with large glass facades to a lake and the forest. The zone lit with zenith light from the glass block roof appears brighter than the window area with side light. On the other hand, the window area provides a beautiful view, while the corridor at the entrance area blocked further views to the outside by means of a glass block façade, which allowed daylight to enter without providing a view. Thus, the transparent glass facades and the translucent glass block elements at the ceiling and the corridor allow for complex intertwining between the dining hall and its surroundings.

Also the color configuration of the bedroom wings belong to the history of the lighting design. Each individual wing had an assigned color—red, yellow, blue, and green—that became brighter from floor to floor.[22] The primary colors established a guidance system for the course participants, who were thus divided in four groups and, quite pragmatically, could easier find their bedroom wing. The color variations strengthened the natural light effect on each floor—darker at the ground, brighter toward the sky.
 

Furthermore, also the staff and instructor housing has a design history. The housing units were initially oriented for optimal lighting, but in the completed units the prevailing ordering system was to orient each room to either a public or a private side. In the competition floor plans all individual bedrooms oriented to south-east, the living room faced south-west with a garden toward the street. The times of the rooms’ occupations were therefore clearly related to the sun position: you wake up with the rising sun and spend your evening hours in the sun-filled living room (fig. 3). The completed housing units were accessed from the street, with living and bedrooms facing away from the street, that is to north-east and south-east (fig. 8). A view toward the south-western street was only possible from the kitchen and the servant room.

The assignments to study the orientation of rooms extended in Hilberseimer’s seminars toward an urban scale. Students investigated necessary building distances for a defined minimum lighting standard and resulting urban configurations.[25] With the help of Bauhaus students Ernst Hegel and Günther Conrad, Hilberseimer published, after the closing of the Bauhaus, the results of these investigations in two articles in the journal Moderne Bauformen. The first article, “Raumdurchsonnung” (1935), which could be translated as “insolation through a room,” included three pages with solar incidence analyses, which look quite familiar by now (fig. 11). Each page is dedicated to a specific day of the year (December 21, June 21, March/September 21) and illustrates a room, represented in a floor plan and three sidewalls, for three different orientations. The top row on each page shows a room facing south, the middle row orienting east, and the bottom row looking to the south-east. In addition, the potential insolation duration (in hours) and the insolation amount (in cubic meter)—in Hilberseimer’s words, the “volume of the solar-radiated air prism” (“Raumgröße des sonnendurchstrahlten Luftprismas”)—was calculated for each room. Hilberseimer’s conclusion that “the south orientation is to be preferred over all other positions”[26] was in opposition to the room orientation preferred by most architects of that time, which was to east and west. The second article, “Raumdurchsonnung und Siedlungsdichtigkeit” (1936), approximately translated as “insolation through a room and urban density,” first demanded for all individual rooms a minimum insolation duration for the day of the winter solstice. On this basis, Hilberseimer developed a formula to determine building distances, from which, in a second step, the population density of cities could be derived (fig. 12).

Hilberseimer immigrated to the USA in 1938 and taught, side by side with Ludwig Mies van der Rohe, at the Armour Institute of Technology, which became later the Illinois Institute of Technology, in Chicago. Solar studies were the foundation of his teaching of urban planning. The university even introduced a “Hilbs Day,” which is celebrated on the day of the winter solstice. This day to memorialize Hilberseimer is still in place and has its origin in the daylight analyses at the Bauhaus.