Lightshelves Save Lighting Energy

Reflect Daylight into a Building to Get Free Easy-on-Eyes Light

Jul 18, 2008

Daylight is the best light for people to work in. Reflectors, or lightshelves, at windows can direct daylight deep into a building, allowing lights to be switched off.

A lightshelf is simply a flat ledge or shelf installed across a window, inside or outside or both, so that it reflects daylight into the building at an angle up on to the ceiling which reflects the light down at an angle.

Lightshelves are suitable for premises such as offices, healthcare facilities, and educational establishments. They cut energy by reducing the amount of artificial lighting needed.

They improve the ergonomic quality of interior light by reducing glare, shadows and sharp changes in contrast, all of which are hard on the eyes. This is especially important for people working at computers.

Best Use of Light

Some research and experience have shown that best light reflection is obtained with eternal and internal shelves installed together at the same height, to maximize the reflective area (see Daylighting Guide for Canadian Commercial Buildings, Public Works and Government Services Canada; U.S. Department of Energy). However, practitioners such as architects Sweeny Sterling Finlayson &Co Architects Inc., (&Co), Toronto, Canada, prefer internal shelves with external shades that direct sunlight on to the shelves.

Location of the building makes a difference. Queen's University, Kingston, Ontario, Canada, has designed a learning centre on 'green' principles where shelves are horizontal. The City of Santa Monica states they should be sloped. The angle of the slope has to be calculated with respect to the mean altitude of the sun and the geometry of the area to be lit.

The shelf surface is often specular (i.e., highly reflective), such as brushed metal. However, where that can produce glare, a less reflective surface is sometimes used. A rough surface can scatter light at many angles, increasing the depth of penetration.

Without lightshelves, sunlight penetrates a building by a depth equal to 1.5 times the window height. Lightshelves can increase that to 2.5 times.

With this much of the building interior lit by reflected sunlight, artificial lighting can be reduced. Light sensors can be installed to switch lights on and off automatically in response to light intensity in sections lit via the lightshelves.

Additional Energy Saving

Best results are obtained with a white or light colored flat ceiling. A ceiling that slopes downwards from the window gives better light distribution and reduces contrast and glare.

However, lightshelves can be used effectively with ceilings that are left open to expose the underside of the concrete slab above, as long as the concrete, beams, ducting, cable trays and other components are white.

This has been done at innovative buildings such as of Microsoft Canada and grocery chain Loblaws in Mississauga, Ontario. Architects &Co designed these buildings to use underfloor distribution of air conditioning with return air ducts above at the open ceiling; this reduces the air conditioning load and the height needed between floor slabs.

In summer, exterior lightshelves or sunshades in any building help to reduce energy for air conditioning by shading windows from solar heat when the sun is high.

Better Lighting for the Eyes

Window glazing above the lightshelf (the ‘daylight’ area) can have a higher visible light transmission (VLT) than the ‘view’ area below to increase the amount of light reflected. Because of shading by external shelves or shades, it is possible in some buildings to improve people’s external view by having a higher VLT glazing than practical without shading.

Blinds fitted to the view area to shade the interior when the sun is low can also be controlled from light sensors to raise and lower automatically depending on the angle and intensity of sunlight.

Lightshelves can be retrofitted to existing buildings. They save energy and improve lighting at no on-going costs. Sunlight is free. Lightshelves help to make best use of it.

The copyright of the article Lightshelves Save Lighting Energy in Office/Facilities Management is owned by Thomas Kelly. Permission to republish Lightshelves Save Lighting Energy in print or online must be granted by the author in writing.