Note: See text of author's paper "Indirect Sunlighting and Skylighting: Strategies used by Alvar Aalto" at end of this section.

Title: Rovaneiemi Library

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Slide #: 002 Author ID: 2 SBSE Slide ID: CD006-002-S001-002 

Title: Rovaneiemi Library

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Title: Rovaneiemi Library

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Title: Rovaneiemi Library

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Title: Rovaneiemi Library

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Title: Rovaneiemi Library

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Title: Riola Church

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Title: Riola Church

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Title: Riola Church

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Title: Riola Church

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Title: Riola Church

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Title: Riola Church

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Title: Imata Church

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Title: Imata Church

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Title: Imata Church

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Title: Imata Church

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Title: Imata Church

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Title: Imata Church

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Seinajoki Library

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Wolfsburg Germany Cultural Center

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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Title: Saynatsalo Town Hall

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A conceptual framework is presented for designer understanding of daylight illumination strategies that utilize large white surfaces as light "sources". LUMINANANCE x APPARENT SIZE is proposed as a simplified conceptural design framework. A series of strategies by the Finnish architect Alvar Aalto that employ white surfaces as light sources is discussed using photographs and matching line drawings from several libraries in Europe and the United States. This paper is derived from a forthcoming book by the author to be published by Van Nostrand Reinhold.

1.0 THINKING ABOUT LIGHT

In order to understand daylighting in general, (and Aalto buildings in particular), it is necessary for the designer to have a conceptual frame of reference.

Slide #: Author ID: Figure 1 SBSE Slide ID: NO SLIDE 

Title: Luminance x apparent size

Comments:

(Figure 1) - LUMINANCE x APPARENT SIZE

Conceptual Framework _ Well suited for considering illumination from distributed source and diffuse paths.

Consider illumination as what can be "seen" by the TARGET. The basis for this approach is that the amount of light at the TARGET is the result of exposure to all of the bright and dim surfaces within the view of that TARGET. More specifically, the light contributed to the target is the product of the LUMINANCE (measured brightness) of a particular source times its APPARENT SIZE as viewed from the receiver. It should be noted that this is an oversimplification if the RECEIVER is a flat plane. Because of the "cosine effect" oblique light does not contribute as much illumination on a plane as does perpendicular light. Moore (1982) has presented a discussion of this approach.

Because daylighting typically employs distributed SOURCES (skyvault) and diffusing PATHS (translucent glazing and white reflective surfaces), this LUMINANCE x APPARENT SIZE method will be used for subsequent discussion. While this method might be unfamiliar to architects, it is widely accepted as the numerical basis for analyzing daylighting and radiation heat transfer.

A matte white surface illuminated by a primary source (i.e., sunlight or skylight) is luminous and can be considered by the designer as distributed light source (similar to a fluorescent fixture) for illuminating a building interior. Aalto made extensive uses of white reflectors as secondary source "fixtures".

Slide #: 026 Author ID: 26 SBSE Slide ID: CD006-026-S001-026 

Title: Seinajoki Library

Comments:

(Figure 2) _ Seinajoki Library

The public library in Seinajoki, Finland is a rich source of examples of his integration of these reflectors into the architectural form of the building. The large, high, south window has clear glazing, with horizontal, diagonal exterior louvers. The louvers are white on both sides with a cut-off angle of 45 degrees. At angles higher than 45 degrees, no sunlight or skylight penetrates directly, but is instead reflected twice by the parallel louvers. As a result, the high window performs like a translucent diffuser to high light sources. Its large area adequately illuminates the reading areas from above the field of view of the reader. The result is generous illumination evenly distributed, little cosine reduction, and minimal glare because of the high source location.

Slide #: 024 Author ID: 24 SBSE Slide ID: CD006-024-S001-024 

Title: Seinajoki Library

Comments:

(Figure 3) _ Seinajoki Library, Exploded Axonometric

At angles below the 45 degree cut-off angle, direct skylight (and in the winter, direct sunlight) enters directly. Most of the direct sunlight strikes the lower part of the large, curved reflective "light scoop". The lower portion of this scoop has a high luminance level (due to its orientation relative to the window). This bright surface becomes the principle source for the vertical book stacks along the exterior wall. Note the large apparent size of the scoop as "seen" from the stack.

Slide #: 030 Author ID: 30 SBSE Slide ID: CD006-030-S001-030 

Title: Seinajoki Library

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(Figure 4) _ Seinajoki Library, Interior showing Light Scoop (explanation diagram slide not included).

The top of the scoop receives light reflected from both the lower part of the scoop as well as the top to the louvers and exterior ground. The exterior wall (below the window and above the stacks) receives light from the lower part of the scoop. While both the upper scoop and this wall portion in turn contribute to the general illumination of the room, their luminance is important in reducing the brightness contrast around the window.

The sunken reading area "sees" two large, bright secondary sources: the high, south window and the north clerestory. The sunken location places both sources high, reducing the cosine reduction from both sources onto a horizontal reading plane, while keeping t hem above the reader's field-of-view to reduce glare.

Most Aalto libraries employ a sunken study area located in the center of the main library space. This creates a strong spatial focus. It also allows stacks to be located in the center without blocking visual control from the circulation desk. In those libraries where light is admitted only from the perimeter, the sunken floor configuration keeps the high side light above the field of view of the reader, while reducing the cosine reduction of illumination on reading tables.

Slide #: 005 Author ID: 5 SBSE Slide ID: CD006-005-S001-005 

Title: Rovaneiemi Library

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(Figure 5) _ Rovaniemi Library, Exploded Axonometric

Slide #: 003 Author ID: 3 SBSE Slide ID: CD006-003-S001-003 

Title: Rovaneiemi Library

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(Figure 6) _ Rovaniemi Library, Interior (explanation diagram slide not included), showing typical bay with sunken reading area, high window and light scoop.

Slide #: 004 Author ID: 4 SBSE Slide ID: CD006-004-S001-004 

Title: Rovaneiemi Library

Comments:

(Figure 7) Rovaniemi Library, Plan with Isolux Contours (percent of exterior horizontal illumination, excluding direct sunlight). The levels of greatest illumination are concentrated in the sunken reading areas.

The last library to be designed by Aalto is located at Mount Angel, Abbey, a Benedictine Monastery near Portland, Oregon. Using a fan-shaped plan, light is introduced over the center reading area by a north-facing, crescent-shaped roof monitor, with a white "scoop" behind clear glazing sloped about 60 degrees. The sectional profile is shallow allowing direct sky illumination in one direction and reflection for the scoop in the opposite. This provides generous illumination in the reading stations surrounding the sunken mezzanine crescent and mezzanine level itself. In addition, adequate light penetrates down past the mezzanine into the basement open stack area to allow selection of books.

Slide #: Author ID: Figure 8 SBSE Slide ID: NO SLIDE 

Title: Mount Angel Library, Interior

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(Figure 8) Mount Angel Library, Interior (with explanation).

Slide #: Author ID: Figure 9 SBSE Slide ID: NO SLIDE 

Title: Mount Angel Library, Interior

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(Figure 9) Mount Angel Library, Interior (with explanation).

Slide #: Author ID: Figure 10 SBSE Slide ID: NO SLIDE 

Title: Mount Angel Library, High North window

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(Figure 10) Mount Angel Library, High North window (with explanation).

On the main level, stacks radiate out from this center light chamber, allowing visual control from the circulation desk. At the perimeter of the main level, open carrels are illuminated from above by high window light which is reflected from the sloped ceiling. This straight "scoop" also washes the wall below the window to reduce brightness contrast of the sky seen through the windows. A similar sloped ceiling is positioned above corner windows in the small lecture room. In addition to light reflected by the sloped ceiling, each lower wall is washed from the adjacent perpendicular window.

3. AALTO BUILDINGS IN PERSPECTIVE

After visiting numerous Aalto buildings, and making detailed illuminance measurements in the six major libraries, this author remains impressed with the breadth and richness of his architectural and illumination vocabulary. In most cases, the two are inseparable. It is easy to be awed by his buildings (and his reputation) and to dismiss them as somewhat mystical creations of a gifted genius. There is a temptation to directly transpose these strategies to the design of contemporary buildings.

This is unwise. Not only were most of Aalto's solutions heavily influenced by local (typically overcast, northerly) daylight environments, they were designed during a time of abundant energy. Little regard seems to have been given to problems of excessive heat loss (or gain). For contemporary architects designing in an environment of clearer skies and much higher relative energy costs, probably the single most valuable principle to be gleaned from Aalto is the use of white surfaces as diffuse, secondary illumination sources. This principle must now be adapted to the preferred use of sunlight (instead of diffuse skylight) to allow smaller glazing areas. The south facing roof monitor (with suitable reflective baffles) for top lighting and the "light shelf" for side lighting are two adaptations of secondary source reflective diffusers to our high sun angles and present energy costs.

4. CONCLUSIONS

The following are design strategies based on Aalto's buildings, but modified for application in U.S. climates and present energy costs:

a.) MAXIMIZE SOUTHERN EXPOSURE

Direct sunlight is easily controlled. Even under overcast conditions, this is the direction of greatest sky luminance, and glass areas can be reduced proportionately. 

b.) IN MULTI-STORY BUILDINGS, USE NARROW PLANS TO MINIMIZE DISTANCES TO PERIMETER LIGHT.

c.) USE SUNLIT WHITE SURFACES AS SECONDARY LIGHT SOURCES.

Position these for (1) maximum exposure to the primary source, and (2) maximum apparent size from the receiving location. This translates to positioning the white reflector approximately as though it were a mirror.

e.) USE WIDE, HORIZONTAL SOURCES in preference to narrow, vertical ones for more even distribution.

f.) USE VERTICAL GLAZING. Sloped and horizontal glazings are difficult to shade during summer months. South vertical glass receives more winter and less summer sunlight.

h.) SUN CONTROL DEVICES SHOULD BE REFLECTIVE (white or mirror) to increase their brightness. This increases their potential as secondary illumination sources while reducing brightness contrast with the visible sky.

i.) USE VERTICAL LOUVERS TO CONTROL SUNLIGHT ON EAST, WEST, AND (if necessary) NORTH GLASS. On east and west locations, angle the louvers toward the north to admit north skylight while excluding morning and afternoon direct sunlight. If the louvers are white, they become secondary sources by reflecting (and thus diffusing) direct sunlight twice before entering.

j.) USE AUTOMATIC, PHOTO-CELL CONTROLLED ELECTRIC LIGHTING. No daylighting system will save energy unless electric lighting is automatically controlled. Manual controls have repeatedly been found unreliable.

k.) USE EXTERIOR HORIZONTAL REFLECTORS BELOW HIGH WINDOWS, CLERESTOREIS, AND MONITORS TO REFLECT LIGHT ONTO WHITE CEILINGS. This is an important strategy for converting the ceiling into a secondary source as well as reducing contrast with the sky. Avoid ceiling obstructions parallel to the glazing (such as beams) that reduce deep penetration of ceiling penetration. Keep these surfaces above eye level to avoid glare to occupants (e.g. locate light shelves on sidewalls above 7'-0").

l.) SURROUND WINDOWS WITH "SOFT FRAMES". Use deep openings so that the surfaces surrounding the window receive skylight, and thus reduce sky brightness contrast. Extend windows to touch adjacent perpendicular walls. In addition to directly reducing brightness contrast at these points, the perpendicular wall reflects light back onto the wall below the window. Slope the soffit up to receive skylight for the same reason.

m.) ADMIST CONTROLLED SHAFTS OF SUNLIGHT INTO NON-CRITICAL AREAS. These add movement and sparkle to the interior.

n.) PROVIDE CONVENIENT BLACKOUT CONTROLS FOR DAYLIGHTED LECTURE SPACES. If these spaces cannot be easily controlled for audio-visual purposes, they will be left dark by the occupants. Several lecture skylights and monitors, designed by Aalto prior to the present widespread use of slide projectors, have been permanently sealed off by the occupants.

5. ACKNOWLEDGEMENTS 

This work was supported by the National Endowment for the Arts, Design Arts Program under a Senior Sabbatical Fellowship. The author wishes to especially thank Jeff Cook, Doug Balcomb, Ed Mazria, and Hayden May for their continuing encouragement. 

6. REFERENCES

Moore, F., "SUNLIGHTING: Toward an Integration of Daylighting and Direct Gain Heating", Proceedings. Seventh National Passive Solar Conference, Knoxville, 1982, pp. 387-92.

Marc Schiler

SBSE

Slides 74-98

Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano Library

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Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano Library

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Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano

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Title: Graves, San Juan Capistrano

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Title: Graves Library, San Juan Capistrano

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Title: Graves Library, San Juan Capistrano

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Title: Graves Library, San Juan Capistrano

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Title: Graves Library, San Juan Capistrano

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Title: Graves lantern

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Title: Graves, Pyramid and lantern

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Title: Graves lantern

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Title: Graves Library

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Title: Graves Library

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Title: Graves Slot

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Title: Graves Library

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Title: Graves Library

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Title: Graves, Sconce

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Title: Graves - Bare tube

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Title: Graves - Inverted pyramid

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Title: Graves - Table lamp

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