This document summarizes a study of the effectiveness of light shelves in illuminating indoor spaces in different geographic regions. Simulations were performed for spaces in Moscow, Russia and Male, Maldives to analyze illumination levels with and without light shelves under various sky conditions. The study found that light shelves effectively bounce light from the window to the ceiling and illuminate the perimeter zone, but not the back wall. Light shelves work best when windows face the equator and receive direct sunlight for a large portion of occupancy hours. Limitations include interference with sprinkler systems and dependence on time of day, year and sky conditions.

1. STUDY OF LIGHT SHELF AND RESULTING ILLUMINATION LEVEL
INSIDE SPACE FOR MALDIVES AND MOSCOW REGION
BACKGROUND INTRODUCTION
The objective of this paper is to understand and highlight the effectiveness of light shelves in different The light shelf is a classical daylighting system, to control and distribute sunlight and skylight, reduce
geographical region and their effect in illuminance level inside the space. Daylight simulations were glare, and improve the interior illuminance in side-lit rooms. (Christoffersen 1995, littlefair 1996). Light
performed for a custom light shelves (plastic material) for a typical space in two different location - 1) shelves are the horizontal devices which help to reflect light from window towards the ceiling and pen-
Moscow, Russia and 2) Male Hulelu, Maldives. Moscow, in Russia, is located at 55.7 degree latitude and etrate little deep in the space. Light shelves are designed to shade and reduce sunlight and skylight
Male Hulelu, in Maldives, is located at 4.2 degree latitude. Simulations were performed using Ecotect near the window, and reflect light from its top onto the ceiling. They have high reflective top surface to
and Radiance and weather data for both the space were taken from U.S Department of Energy website. enhance the reflection of light towards the ceiling. Light shelves are typically used in big bulky buildings
Simulation readings were taken both for sunny as well as overcast sky, during 21st of March, June and where it is difficult for light to penetrate deep inside or places where sky is over casted most of the time.
September. For Maldives, readings are taken at 9 AM, 12 PM and 3 PM of day and for Moscow, readings
were taken at 9 AM, 12 PM and 5 PM. Along with variation in day and time, reading were also taken IMPORTANT: LIGHT SELF BOUNCE LIGHT FROM SHELF TO CEILING WHICH THEN GETS BOUNCE TO THE
having variation in location of light shelf - both side of wall (inside and outside), only exterior side of wall PERIMETER ZONE ONLY AND NOT AT THE BACK WALL.
and only interior side of wall and compared with same situation of day and time without light shelf. The
space taken for study was a small room with dimensions of 4.5 M x 6 M with height of 3 M. The smaller
faced with width of 4.5 M faces south and has a opening and light shelf. No opening are there on other APPLICATION
sides - East, West and North. Height of light shelf is 2.1 M from ground and is 0.6 M in width both inside
and outside the wall. Length of light shelf is 3.9 M and is centrally placed on the facade of 4.5 M leaving • Light shelves require direct sunlight. The windows should face the sun for a larger fraction of time
wall edges of 0.3 M both the sides. Illumination range inside the space is not tried to be maintained in that the space is occupied. As a result, they are more advantages to place on windows facing equa-
specific range of comfort. It is used in pure form as obtained by the conditions available. Analysis grid for tor.
the space is divided into grid of 21 x 17 units with 21 units at facade of 4.5 M width. Analysis of results • They are generally mounted with window having large area of glazing over the height of 2.1 m (7 ft.).
is based only for the central grid and not any other portion of the grid, and hence space. • The glazing that directs light on the light shelves is required to be clear glass, in order to receive suf-
ficient light to reflect. Tinted or Colored glass reduces the intensity of income light. More smoother
KEYWORDS the surface, more will be the reflection.
• Depending on quality of light required, finishing layer of light shelves and the ceiling can either be
Illuminance Level, Light shelves, Sunny Sky, Overcast Sky, With Light Shelf, Without Light Shelf. smooth or rough.
STUDY MODEL LIMITATIONS
• The extension of light shelves inside the room may result in interface with sprinkler system. In Can-
ada, they cannot exceed 1200 mm (4 ft.) in width if sprinklers are present or the design will require
integration with sprinkler system to cover the floor area under the light shelf.
• The illumination range and level inside the space depends both on time of day and year and also on
sky conditions.
• Light shelves needs regular maintenances in terms of cleaning in order to have proper and sufficient
reflection of light off the shelf to the ceiling.
ELEMENTS INVOLVED
• Light Shelf - Reflector
• Window
• Ceiling
• Shading device(s)
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2. LIGHTING PATTERN OF THE LIGHT SHELF SYSTEM CASE STUDY - NREL Campus, Colorado
• The pattern of illumination depends on the reflection characteristics
of the light shelf, and it depends on the geometry and reflection char-
acteristics of the ceiling surface.
• If the reflection by the light shelf is specular, the reflection is con-
trolled by the law of optics where reflection equals the angle of inci-
Light shelf and system
dence.
• If the sun is low in the sky, sunlight penetrates deeply into the space.
If the sun is high, the ceiling is illuminated close to the wall.
• Pure specular reflection creates a sharply defined rectangular bright
spot on the ceiling. This might be bright enough to annoy occupants.
This effect can be reduced by making the reflecting surface of light
shelf more diffuse. Hence light spreads out on the ceiling.
• If the reflection is very diffuse, penetration into the space is sacri-
ficed. A taller ceiling provides deeper light penetration, and it also
distributes the light more widely within the space. High sun angle – Less penetration
• Under overcast sky, the light shelf reduces the illumination level on and more intensity
the working plane because it directly cuts off part of view to the sky.
• The magnitude of reduction at a given point depends on the distance
from the light shelf and the position and depth of the light shelf.
• An interior light shelf at normal height would thus screen off most
of the light from the sky on the working plane in the middle of the
room, while an exterior light shelf would do this mostly in the area
just inside the window.
Low sun angle – More penetra-
tion and less intensity
STUDY REGION
A) COLORADO -
US
LATITUDE - 39.74
B) MOSCOW -
C RUSSIA
A LATITUDE - 55.7
TROPIC OF CANER C) MALE ISLAND -
MALDIVES
EQUATOR B LATITUDE - 4.2
• 100% of the workstations are daylit
TROPIC OF CAPRICORN • No employee is more than 30 feet of the window
• Daylighting controls that works
• Manual on, manual off with vacancy sensors and local dimming controls in all daylit zones.
• Run dark at night, including most emergency lighting - less than 5% of lights on at night
• Interior integrated with daylight.
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3. 21st JUNE SUNNY SKY 21st JUNE OVERCAST SKY
STUDY 1 - MALE, HULELY - MALDIVES
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
Interior - Exterior
ANNUAL SUN MOVEMENT SKY – MALDIEVES OVERCAST SKY - MALDIEVES
The movement of sun at Maldives is almost 6000 6000
over head. So there are similar sun angles 5000 5000
LUX LEVELS
LUX LEVELS
4000 4000
and altitude for other half of year. As a result 3000 3000
of which sunlight penetrate at almost similar 2000 2000
1000 1000
angle in the room, at early morning and late 0 0
afternoon and has similar illuminance level 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
inside the space. Not much difference was
found in illuminance level with and without ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
SKY - MALDIEVES OVERCAST SKY - MALDIEVES
light shelf during month of March, for both 6000 6000
sunny and overcast sky. As there are no open-
Exterior
5000 5000
LUX LEVELS
LUX LEVELS
ing on the north facade, there is no much ef- 4000 4000
3000 3000
fect found in month of June when sun is in the 2000 2000
north. During December, as sun is the south, 1000 1000
0 0
once can see remarkable effect of difference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
of illuminance in space with and without light
shelf during sunny sky condition. It is impor- ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
tant to note that there is not much effect of SKY - MALDIEVES OVERCAST SKY - MALDIEVES
light shelf during overcast conditions. Other 6000 6000
5000 5000
significant result was that illuminance level
LUX LEVELS
LUX LEVELS
Interior
4000 4000
are almost similar at the end of the space, for 3000 3000
2000 2000
both case of with and without light shelf. Also, 1000 1000
for the cases with light shelf, there is little in- 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
crement in the illuminance level at periphery
region only near the window.
21st MARCH SUNNY SKY 21st MARCH OVERCAST SKY 21st DECEMBER SUNNY SKY 21st DECEMBER OVERCAST SKY
Interior - Exterior
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
Interior - Exterior
SKY - MALDIEVES OVERCAST SKY - MALDIEVES SKY - MALDIEVES OVERCAST SKY - MALDIEVES
6000 6000 40,000 40,000
5000 5000 35,000 35,000
30,000 30,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
4000 4000 25,000 25,000
3000 3000 20,000 20,000
2000 2000 15,000 15,000
10,000 10,000
1000 1000 5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
SKY - MALDIEVES OVERCAST SKY - MALDIEVES SKY - MALDIEVES OVERCAST SKY - MALDIEVES
6000 6000 40,000 40,000
Exterior
35,000
Exterior
5000 5000 35,000
30,000 30,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
4000 4000 25,000 25,000
3000 3000 20,000 20,000
2000 2000 15,000 15,000
10,000 10,000
1000 1000 5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
SKY - MALDIEVES OVERCAST SKY - MALDIEVES SKY - MALDIEVES OVERCAST SKY - MALDIEVES
6000 6000 40,000 40,000
5000 5000 35,000 35,000
30,000 30,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
Interior
Interior
4000 4000 25,000 25,000
3000 3000 20,000 20,000
2000 2000 15,000 15,000
10,000 10,000
1000 1000 5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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4. 21st JUNE SUNNY SKY 21st JUNE OVERCAST SKY
STUDY 2 - MOSCOW, RUSSIA
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
Interior - Exterior
ANNUAL SUN MOVEMENT SKY - MOSCOW OVERCAST SKY - MOSCOW
The movement of sun at Moscow is 40,000
35,000
40,000
35,000
from south. Moreover the altitude 30,000 30,000
LUX LEVELS
LUX LEVELS
25,000 25,000
of sun during December is extremely 20,000
15,000
20,000
15,000
low. Effective results were found for 10,000
5,000
10,000
5,000
illuminance level inside space for 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
both the cases, with and without
light shelf. Depending on location of
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
light shelf and time, it allowed sun- SKY - MOSCOW OVERCAST SKY - MOSCOW
light penetration accordingly and 40,000 40,000
35,000 35,000
Exterior
gave illuminance level accordingly. 30,000 30,000
LUX LEVELS
LUX LEVELS
25,000 25,000
Here too, as in Maldives, no effect of 20,000 20,000
illuminance level changes occurs in 15,000 15,000
10,000 10,000
overcast sky. Interesting result were 5,000
0
5,000
0
found for December when sun is at 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
the lowest angle and as a result of
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
which there is no effect of light shelf. SKY - MOSCOW OVERCAST SKY - MOSCOW
Sunlight enters the room directly 40,000
40,000
during December and because of 35,000 35,000
30,000 30,000
LUX LEVELS
that illuminance level increase at the
Interior
Axis Title
25,000 25,000
20,000 20,000
end of the space. 15,000 15,000
10,000 10,000
5,000 5,000
0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
21st MARCH SUNNY SKY 21st MARCH OVERCAST SKY 21st DECEMBER SUNNY SKY 21st DECEMBER OVERCAST SKY
Interior - Exterior
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
Interior - Exterior
SKY – MOSCOW OVERCAST SKY - MOSCOW SKY - MOSCOW OVERCAST SKY - MOSCOW
40,000 40,000 8,000 8,000
35,000 35,000
30,000 30,000 6,000 6,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
25,000 25,000
20,000 20,000 4,000 4,000
15,000 15,000
10,000 10,000 2,000 2,000
5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
SKY - MOSCOW OVERCAST SKY - MOSCOW SKY - MOSCOW OVERCAST SKY - MOSCOW
40,000 40,000 8,000 8,000
Exterior
35,000 35,000
Exterior
30,000 30,000 6,000 6,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
25,000 25,000
20,000 20,000 4,000 4,000
15,000 15,000
10,000 10,000 2,000 2,000
5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE - SUNNY ILLUMINANCE LEVEL IN THE CENTER OF THE SPACE -
SKY - MOSCOW OVERCAST SKY - MOSCOW SKY - MOSCOW OVERCAST SKY - MOSCOW
40,000 40,000 8,000 8,000
35,000 35,000
30,000 30,000 6,000 6,000
LUX LEVELS
LUX LEVELS
LUX LEVELS
LUX LEVELS
Interior
Interior
25,000 25,000
20,000 20,000 4,000 4,000
15,000 15,000
10,000 10,000 2,000 2,000
5,000 5,000
0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
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5. OBSERVATION AND CONCLUSION
GENERAL
• Light shelves does not work well for places which has major overcast sky conditions throughout year.
• Helps well in decreasing the peripheral glare and discomfort
• Effect of inside illuminance and reducing peripheral glare and discomfort depends on width of light shelf, location (inside, outside or both), vertical positioning, its angle and also on dimensions and type of glaz-
ing.
• Depending on the requirement of the space, one can decide upon having light shelf either interior, exterior or both, as they all have different effect on illumination at interior space near perimeter.
• Not much effect have been seen at the end of the space using either of 3 cases.
MARCH JUNE DECEMBER MARCH JUNE DECEMBER
SUN MOVEMENT - MALE - HULELU, MALDIVES
9 AM
9 AM
SUN MOVEMENT - MOSCOW, RUSSIA
12 PM
12 PM
5 PM
5 PM
MALE - HULELU, MALDIVES MOSCOW, RUSSIA
• For location near equator, light shelf doesn’t work during months around March and September as • For location moving far above tropic of cancer, light shelf doesn’t work during months around De-
sun is almost overhead. cember as sun is at very low altitude, even during noon time.
• Light shelf works equally well for north and south façade. • Light shelf works well for months between months from March to September as sun is at higher
• Illuminance level is almost similar inside space in the central part during early morning (9AM) and altitude compared to other months.
late afternoon (3PM) as sun penetrates the space at almost similar angle from south.
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