Skylights can significantly improve natural daylighting in commercial buildings, but whether they save more energy than they add in cooling depends on their design, size, glazing, climate, roof orientation, and lighting controls. The simple answer is no—not necessarily. A properly designed skylight system can reduce electric lighting demand while keeping solar heat gain under control. However, poorly selected or oversized skylights can increase cooling loads enough to offset some or all of the lighting savings.
How Skylights Reduce Lighting Costs
Skylights bring natural light directly into areas that may otherwise require artificial lighting throughout the day. This is particularly valuable in large commercial facilities such as warehouses, distribution centers, manufacturing plants, retail stores, and other buildings with large roof areas.
When skylights are combined with daylight-responsive lighting controls, electric lights can automatically dim or switch off when sufficient daylight is available. The U.S. Department of Energy notes that properly integrated daylighting can reduce lighting energy, peak electrical demand, and cooling energy.
This matters because conventional electric lighting produces heat. When lighting fixtures operate less frequently, the building not only consumes less electricity for lighting but may also require less air conditioning to remove the heat generated by those fixtures.
Why Skylights Can Increase Cooling Loads
The main concern is solar heat gain. A skylight allows sunlight—and therefore solar energy—to enter the building. During hot weather, that additional heat can increase indoor temperatures and make the HVAC system work harder.
The U.S. Department of Energy identifies the solar heat gain coefficient (SHGC) as an important factor when evaluating fenestration products such as skylights. A lower SHGC generally means less solar heat is transmitted into the building. Visible transmittance (VT), meanwhile, indicates how much daylight passes through the glazing.
The goal is therefore not simply to install as much transparent roof area as possible. The objective is to achieve the right balance between daylight transmission and solar heat control.
When Skylights Are More Likely to Deliver Energy Savings
Skylights tend to perform better when they are carefully sized and paired with efficient glazing and automatic lighting controls. Diffusing skylights can distribute daylight more evenly, reducing glare and helping illuminate a larger portion of the occupied space.
Building use also matters. A warehouse with high daytime lighting requirements may benefit substantially from daylighting because the skylights can reduce the operating hours of high-wattage fixtures.
A DOE case study of a Best Buy facility found that a daylight-harvesting system using skylights and dimmable lighting reduced lighting energy use by an average of 45% in the store.
When Cooling Can Become the Bigger Problem
Skylights can become less attractive when they are oversized, use high-solar-gain glazing, lack effective daylight controls, or are installed without considering the building’s climate and HVAC requirements.
In hot climates, uncontrolled solar heat gain can be especially costly because cooling systems must operate longer to maintain indoor comfort. Poorly designed skylights can also create glare, hot spots, and uneven daylight distribution.
That is why the Department of Energy emphasizes controlling direct sunlight and balancing daylight with solar heat gain when designing daylighting systems.
The Bottom Line
Skylights do not automatically increase cooling loads more than they reduce lighting costs. Their overall energy performance depends on the complete roof and building design.
For commercial properties, the best approach is to evaluate skylight area, glazing performance, SHGC, visible transmittance, daylight distribution, lighting controls, HVAC loads, and local climate together. Energy modeling can also help determine whether a proposed skylight system will produce a net energy benefit before installation.
For an existing commercial roof, property owners should also consider the condition, age, leaks, insulation, and energy performance of the existing skylights before adding or replacing them. A roofing professional can help determine whether improving existing skylights, replacing them with higher-performance units, or reducing unnecessary roof glazing is the most practical solution.
In short: well-designed skylights can reduce lighting and even cooling energy, while poorly designed skylights can increase cooling loads and erase the expected savings. The key is controlled daylight—not simply more daylight.
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