What are light shelves? A Comprehensive Guide

Humans require natural light to survive. We need it to see, to regulate our circadian rhythms, and to feel happy.

That is why it is critical to bring as much natural light as possible into our buildings.

To achieve this goal, building designers are constantly testing new strategies. They utilize different window-to-wall ratios, different window shapes, sizes, and placements to optimize their daylighting designs.

However, introducing daylight into a building presents its own set of challenges.

For example, glare can be a major issue if prevention is not planned ahead of time. Because it is the unintended light that creates problems like excessive brightness, reflections, and as a result occupant discomfort.

Also, in some cases, the direct sunlight can be too intense and reduce occupant thermal comfort while increasing cooling energy consumption.

Although we want to have as much natural light as possible in our buildings, we don’t want it to randomly come in through windows.

Aside from that, for many building designs, it may not always be possible to install enough windows, skylights, or other openings into a building due to security, climate, or budgetary concerns.

Most buildings, even those with a lot of glazing, don’t let in as much natural light as they could.

The received daylight usually can only reach a few workstations around the perimeter, leaving the rest of your occupants in the dark.

This can cause occupants not to have enough exposure to natural daylight and feel tired, unmotivated, and as a result less productive.

Most projects’ daylighting efforts fall short of their potential not because of the lack of windows. But rather a lack of a plan for controlling how daylight should be introduced to the space.

There are many daylighting control strategies that can be used to mitigate these problems.

But one of the most efficient and least expensive strategies is using light shelves.

It is a relatively new strategy that architects have been using to increase the amount of daylight, reduce glare, and improve energy efficiency.

Light shelves reflect natural sunlight into a building while also diffusing it to reduce glare and shadows. They increase the amount of daylight in a space without taking up any additional floor space.

What is a light shelf?

A light shelf is a baffle that is installed partway up a window to control and redistribute incoming light.

It is a passive architectural element that is adjusted in a horizontal or near-horizontal position to bounce light off its surface and into the room.

Typically, the light shelf’s lower surface is a matte finish, while the upper surface is made of specular mirror panels that reflect sunlight back into the space.

A light shelf typically has a low profile and is unobtrusive from the outside, making it an excellent choice for architects who want to maximize natural light without sacrificing the appearance of their building.

When sunlight hits the light shelf, it is directed toward the room’s ceiling and walls.

This increases the amount of light that enters the space without needing to increase the size of the windows.

Because light shelves are typically installed on the higher top portion of a window, they catch and redirect sunlight that would otherwise be impossible to penetrate into the room.

Should you have an internal or external light shelf?

Light shelves can be installed both inside (internal light shelve) and outside (external light shelve) of a building depending on the project’s priorities.

Both choices have their own plus and minus we are going to discuss further.

What is an internal light shelf?

An internal light shelf is a light shelf that is installed on the inside of a building. It starts from the window and goes into the room.

Internal light shelves are an excellent choice because they do not require any additional construction or building modifications that are required to be done outside the building.

They are typically easier to install and less expensive than external light shelves.

Since internal light shelves are inside the building, they can be made to fit perfectly with any architectural design. Weather conditions are never a concern with internal light shelves.

What is an external light shelf?

An external light shelf is a light shelf that is installed on the outside of a building. It starts from the window and extends out into the open.

External light shelves have a few advantages over internal light shelves. They better maximize daylighting potential compared to internal light shelves because they are outside the building.

Since they cover a more uninterrupted surface area, they are more likely to capture and redirect all available sunlight.

However, they are not as effective as internal light shelves in transferring daylight into the building because they don’t offer a direct path from the window to deeper interior space.

They are also more difficult and expensive to install than internal light shelves.

External light shelves can be affected by weather conditions like rain, snow, and winds which will require extra care and maintenance.

Are there any light shelves that cover both the inside and outside of a building?

Yes! There are light shelves that extend both inside and outside of a building.

So, part light shelf stays on the inside, and part stays on the outside. Light shelves that cover both the inside and outside of a building are an excellent choice because they offer all the benefits of both internal and external light shelves.

There are different designs with different proportions of light shelves staying inside or outside of a building.

How high up can light shelves be installed?

Light shelves work best in spaces with high ceilings. Because a light shelf will naturally occupy a certain amount of window height from the top blocking the daylight from entering the window.

A low-hanging light shelf will largely defeat the purpose of using a light shelf in the first place.

Because it will create shades and dark areas in the space. The lower light shelf may also obstruct people’s view of the outside, visually reduce ceiling height, and make people near windows uncomfortable.

However, it is worth noting that a good compromise must be made in order to determine the optimal height, as it may have a significant impact on performance efficiency.

What type of projects can benefit from light shelves?

Light shelves are a great tool for any project that may benefit from natural lighting.

They can be used in both residential and commercial buildings. However, in order to be effective, they should be implemented early in the design process to ensure they are properly sized, positioned, and tested.

Also, both new and existing buildings can benefit from light shelves. However, implementing light shelves in an existing building will require more work.

Because light shelf installation will require additional design, construction, in some cases permitting applications since it may be counted as a structural alteration depending on the building’s code.

Light shelves tend to provide better results in rooms that have higher ceilings.

Because it allows planning a larger glazing area at the top that will allow capturing daylight coming from a larger range of angles.

One big benefit of light shelves they don’t block views and can be used in conjunction with other daylighting controls.

If you plan to have light shelves for your project you need your building interiors to have light colors to reflect light better.

Because having light shelves without light colors will not reflect the daylight as much and you’ll lose all the benefits of using them.

It is also important to choose the glazing smart if you are choosing to use light shelves.

A lot of manufacturers will provide you with “The Visual Transmittance Value” of their glass, which indicates how much pure daylight the window will let in.

Ideally, you need to choose the type of glass that is spectrally selective and that will allow for more daylight while rejecting heat gain.

What to pay attention to implementing light shelves in a building?

Although light shelves are a great tool for bringing natural light into buildings, they need to be implemented correctly. This requires some planning, design, and testing work.

Here are some things to consider when implementing light shelves.

Building Orientation

The orientation of the building will play a key role in the effectiveness of light shelves.

Although light shelves can be used on any type of building orientation, certain orientations will be better suited for light shelf installation.

For example, light shelves are especially suited to areas with strong levels of sunlight on windows facing south or north in near-equatorial latitudes.

However, rooms that face east and west will have a longer amount of sunlight exposure throughout the day, which makes them better candidates for utilizing natural lighting while reducing glare.

Width and Installation Height of Light Shelf

Light shelves should be wide enough to allow sunlight to penetrate but not so wide that they cast a shadow inside the room.

Architects should test different widths in their mockups or models until they achieve the best results for each space in order to find this optimal width.

Installation height is also critical and should be taken into account when sizing the light shelf.

Light shelves should be installed at one-third the height of the window from above as a general rule. This allows for maximum light penetration into a room while preventing shadows from forming within it.

A light shelf’s width should be roughly the same as the height of the vertical glass above it. This will allow light to reflect a distance of about two and a half times that height.

For example, if you have 4 feet of vertical glazing above your light shelf, your light shelf should be 4 feet wide. This will create 10 feet of daylight penetration into the floor plate.

Material and Color of Light Shelf

Light shelves should be made out of a light-colored material to reflect sunlight into the room.

The color white is ideal for this purpose as it will reflect all colors of daylight equally well.

However, the important part here is not the color of the material itself, but rather the reflective properties of the surface.

There are a number of manufacturers that provide a reflective paint or coating on their light shelves to increase their product’s reflective properties.

When it comes to materials, you have a lot of options to choose from. There are aluminum, glass, engineered wood, or polycarbonate light shelves that are surface treated with powder-coated paint that reflects light.

But the important thing the selected material should be durable and easy to clean especially if it is going to be installed building exterior.

Window Cleanliness and Clarity

Light shelves can only be effective as much as the window system allows for optimal daylighting.

If the glass is dirty it will not allow for as much sunlight to pass through and light shelves will be less effective at bringing in natural lighting.

Dirty windows can reduce the amount of natural sunlight passing through them by up to 50%.

As a result, if you want to maximize the effectiveness of light shelves, you will need to regularly clean your windows.

Window Size & Shape

The size and shape of windows also have an impact on the effectiveness of light shelves.

To be effective, windows used to implement light shelves should have a large surface area and a small frame size.

The size and shape of both windows and light shelves are also factors that need to be tested before being implemented for a specific space.

This testing should ideally take place on a physical model of the space to ensure that both components have their optimal size and location.

Shading Requirements

The shading demands determine the minimum depth of an external light shelf.

The greater the depth, the more it shades the window below, preventing direct radiation from reaching it and causing glare and solar gains.

The depth required for east and west-facing facades varies with orientation.

Orientation and LatitudeRequired Depth of Light Shelf
Near-equatorial latitudes1.25 to 1.5 times the height of the ribbon window above
Latitudes more than 20° off south/north1.5 to 2.0 times the height of the ribbon window above

Depending on the sun’s path, the depth of the interior light shelf in a room facing south or north may be about equal to the height of the ribbon window above.

To achieve a successful result, the window height, depth of the light shelf, and height of the glazed ribbon above should all be evaluated in relation to the actual latitude, climate, and orientation using appropriate mathematical tools.

Can you pair light shelves with daylight sensors?

Light shelves can be paired with daylight sensors to adjust the positioning of the shelf.

When the sensor detects that the sun has moved to a new position in the sky, it can then tilt the shelf to position receiving the most amount of sunlight possible.

This is generally achieved by using a motorized system that can tilt the shelf in response to a signal from the daylight sensor.

Using such a system you can maximize the amount of sunlight that is able to make its way into a room.