Skylights: Naturally Lit Interiors Save Energy

Skylights: Naturally Lit Interiors Save Energy

Skylights are one surprising design option for a commercial building that needs to save on energy. Skylights offer many benefits including savings on artificial lighting and heating. One of the largest sources of energy consumption in commercial and industrial applications is artificial lighting.

Skylights impact the building’s energy usage in three ways, two positive and one negative, though the two positive benefits more than make up for the negative one. Skylights save energy by replacing artificial lighting with adequate natural light. This is a positive effect. Another positive effect is the amount of heating energy saved as a result of passive solar gain. (This can be a complex benefit since the design of the building and other construction materials will determine how much passive solar gain there is.) Unfortunately, skylights can lead to some heat loss, though not enough to make skylights a poor decision.

More About Skylights

Current skylights consist of insulating glazing held in aluminum frames in one of many configurations such as single slope, ridge, pyramid and barrel vault. Skylights have been used for more than a century to provide daylight to interior spaces. Early skylights consisted of plate glass — and later, wire glass — in metal frames. They frequently included both an exterior skylight and a second layer on the bottom, a decorative “diffuser” or “laylight.”

Skylights Provide Energy Savings

Some might think that having a surplus of skylights allow more heat to escape than the rest of a roof thereby increasing the running costs of the building. Research from the Institute of Energy & Sustainable Development proves that assumption wrong. Instead, the Institute finds that installing the appropriate number of skylights can reduce overall energy consumption.

Well-designed buildings with abundant natural light experience passive solar gain and need less artificial light. This means that including skylights in building design can offer a dramatic reduction in a building’s total energy consumption as well as reduced CO2 emissions. The benefits of a naturally-lit interior include the reduced energy consumption and reduced emissions, money savings, and a more pleasant environment where people what to spend time.

These are the findings of the study that the National Association of Rooflight Manufacturers (NARM) commissioned from the Institute of Energy & Sustainable Development at Leicester’s De Montfort University.

Daylight has many advantages over artificial light including that it’s an entirely free and unlimited natural resource.

When assessing the overall impact of skylights and glazing on a building’s energy efficiency of a building, there are a lot of factors to consider.

Lux is the measurement of lighting level. A light level of 300 lux is adequate for activities that don’t require the perception of detail; it is suitable for circulation spaces and assembly halls. When a degree of color judgement is required as in many retail, production and office environments, a light level of 600 lux is ideal.

An increase in skylight area, at least within the range of 0 and 20 percent, results in the reduction of total CO2 emissions.

In buildings used primarily during daylight hours during colder months, skylights actually decreases the amount of energy required for heat. For a building that is occupied between 9 a.m. and 5 p.m. for 365 days with a lighting requirement of 600 lux whose roof is 20 percent skylights, there is an impressive 85 percent savings in CO2 emissions from lighting and heat loss over the same building without skylights. When a building with skylights is occupied 24 hours a day, there are no benefits from natural light or passive solar energy.

Yet even at night, skylights can provide a significant energy benefits. When a commercial space requires a lighting level of 600 lux, energy savings are proportionate to the amount of skylight area. The more skylights there are, the better the energy savings. This is especially true for buildings that have a lighting requirement of only 300 lux, which is relatively low. In these low-lit buildings, energy consumption falls even further as the skylight area increases. In buildings that require a lighting level of just 300 lux until it reaches 14 percent.

Get the Most Out of Skylights with Automated Lighting Controls

Because of cloud movement, the amount of sunlight that comes through skylights

Research shows how important appropriate lighting controls are to maximizing the energy savings benefit. Even with skylights, artificial lights are often left on even when not needed. If artificial lights are left on even when sunlight is strong enough that the artificial lighting isn’t needed, the considerable energy savings that skylights offer are lost.

Ensure savings by using simple “on/off” automated lighting controls. These turn on all the artificial lights when sunlight is lost and lighting levels fall below the required lux level. To earn maximum savings, an automated lighting control system that turns on only enough artificial light to maintain the required lux levels is the best choice.

Skylights Provide Numerous Benefits to Commercial Buildings

Skylights have an overall effect of energy savings and reduced CO2 emissions. The bright, natural light let into an interior by skylights help create a pleasant environment, help inhabitants feel better and concentrate better, improve the building’s functionality and reduce energy consumption. All of these make skylights an ideal solution for commercial buildings.

Energy Efficient Windows & Doors

Whether your company is working on plans for a new building or looking to renovate or add onto an existing property, you can find energy-efficient windows, doors and skylights to fit your needs. First, though, you have to understand a few basic principles including how these glass products gain and lose heat, energy performance ratings, and energy performance characteristics such as U-factor, solar heat gain coefficient and air leakage.

Windows, doors and skylights gain and lose heat in three ways:

(1) Direct conduction through the glass, glazing, frame and/or door.

(2) Radiation of heat, typically generated by the sun, into a house, and the loss of heat out of the house through room-temperature objects such as people, furniture and interior walls.

(3) Leaking of air through and around doors, windows and skylights.

That doesn’t mean you can’t reduce the amount of heat loss or increase the amount of heat gain. By choosing and using energy-efficient windows, doors and skylights, you can protect the environment, reduce the costs of heating and cooling your company headquarters, and enjoy a naturally lit work environment.


The energy performance ratings of windows, doors and skylights indicate the product’s potential for heat gain and heat loss. Energy performance ratings also tell you how much potential the window, door or skylight has for allowing sunlight into your home.

How do you know what a window or door’s energy performance rating is? All ENERGY STAR qualified windows, doors and skylights carry labels or stickers from the National Fenestration Rating Council (NFRC). The NFRC runs a voluntary program that tests, certifies and labels windows, doors and skylights based on their energy performance ratings. These NFRC labels enable consumers to reliably determine the product’s energy properties and compare with other windows, doors and skylights.

ENERGY STAR, a government-backed program, provides information on energy efficiency and enables businesses and individuals to protect the environment. ENERGY STAR qualifications are based solely on U-factor and solar heat gain coefficient (more on these later).


You must choose, position and size your windows in a specific way to maximize solar heat gain. In very hot climates, you want big windows facing the south to collect solar heat in the winter, as this is when the sun hangs lowest in the sky. By summer, the sun has risen high overhead. That’s when you’ll want overhangs and other shading devices on those south-facing windows so that you can prevent excessive heat gain, thereby reducing the costs of cooling the house.

On, it’s recommended that you minimize the use of Windows on walls that face north, east and west while still allowing for adequate daylight. This is because it is difficult tocontrol heat and light through east- and west-facing windows when the sun is low in the sky. East- and west-facing windows, doors and skylights should be shaded and/or have a low solar heat gain coefficient. North-facing windows are used solely for light purposes as they collect little solar heat.

In addition to using shading to help control solar heat gain, you can purchase windows with low-emissivity (low-e) glazing.


Using the folloing energy performance characteristics, you can measure and rate the heat loss and heat gain properties of windows, doors and skylights.

– U-factor is usually expressed in units of Btu/hr-ft2-oF. This is the rate at which a window, door, or skylight conducts non-solar heat. A U-factor may refer solely to the glass or glazing, but NFRC U-factor ratings refer to the entire window or door’s performance. This includes frame and spacer material. Windows, doors and skylights with lower U-factors are more energy-efficient.

– The fraction of solar radiation admitted through a window, door or skylight is called solar heat gain coefficient. This solar radiation is either transmitted directly and/or absorbed. It issubsequently released inside the home as heat. The amount of solar heat a window, door or skylight transmits and the greaterits shading ability, the lower the solar heat gain coefficient will be. “A product with a high SHGC rating is more effective at collecting solar heat during the winter,” according to lower the product’s solar heat gain coefficiency rating, the better it will be at reducing the amount of cooling needed in the summer. Your building’s climate, orientation and external shading determine the optimal solar heat gain coefficient for a particular window, door or skylight.

– Air leakage, expressed in units of cubic feet per minute per square foot of frame area (cfm/ft2), is the rate of air movement around a window, door or skylight in the presence of a specific pressure difference. The tighter the product frame, the lower the air leakage will be.


There are two energy performance characteristics that can be used to measure and rate a window, door or skylight’s ability to allow sunlight into a building: visible transmittance and light-to-solar gain.

– Visible transmittance: A fraction of sunlight’s visible spectrum (380 to 720 nanometers) that enters a building through the glazing of a window, door or skylight. The higher the visible transmittance, expressed as a number between 0 and 1, the more visible light flows through a window, door or skylight. The visible transmittance you need for a window, door or skylight is determined by your building’s daylighting requirements. Another consideration is how much reduction of interior glare the space needs.

– Light-to-solar gain is the ratio between the solar heat gain coefficient and visible transmittance, which is a gauge of how efficient different glass or glazing types are at allowing daylight in while blocking heat gains. The higher the light-to-solar gain rating, the more light is allowed in while avoiding excessive amounts of heat. Light-to-solar gain ratings aren’t always provided on products.