Sun Hours Analysis and cove.tool

Sun Hours, Sunlight, Solar Exposure, Rights to Light Laws, and more

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

Along with sDA & ASE, radiation, and shadow 3D visualizations, cove.tool also analyzes your building's envelope for the annual hours of direct sunlight.

What is a Sun Hours Analysis?

Sun Hours, also known as exterior solar exposure, measures the average number of hours your building envelope receives unobstructed daylight over a typical year. This analysis type is unique from the other 3D analyses because this simulation has its origins in the Rights-to-Light laws. Rights-to-Light laws entitle building owners and local governments to deny new construction of buildings whose size, shape, and location obstruct pre-established "sufficient daylight" to existing buildings and public parks. To analyze "sufficient daylight" claims, a sun hours analysis and shadow study are undertaken to prove the damaging or insignificant daylight impact of a new building. Sun hours analysis has also proven useful for providing insight relevant to programming, furniture layouts, shading strategies, and landscape placement. Being able to guarantee that residents of an apartment building get good sunlight is a big selling point for developers.

Calculation Method

Taken from the "CEN European Daylight Standard (EN 17037): Section 5. Assessment of Daylight," cove.tool uses the weather file's skydome to calculate the number of rays (sun hours) that reached the building envelope (unobstructed) with a minimum intensity of 300 lux. Using raytracing, the simulation engine employs a Tregenza skydome with 576 subdivisions and an hourly analysis period of the typical year. To present these results, cove.tool:

  • renders a heatmap along the building envelop that represents the annual percentage of daylight (>300 lux) received by that surface, and

  • displays the annual average of daily sun hours.

EN 17037 is a standard that is also popular for creating protect view analyses. This analysis can also be used to evaluate the number of hours of sunlight received by vegetation in a park or the hours where direct sunlight might make a certain outdoor space comfortable or uncomfortable.

Why have a sun hours analysis for your building?

Light enables the use and enjoyment of our homes and workplaces, allowing people to live and work in safety and comfort. The importance of lighting in the workplace and at home is recognized by law. For example, there are numerous and varied codes around the world that reserve daylight rights to buildings owners and also guarantee a certain amount of daylight to each window. These regulations are some of the first building standards established around the world and therefore also known as Ancient Lights. In America, these rights began to be abolished in the 19th Century as electric lighting became popular. However, these rights are reappearing in America and are more stringent in Europe.

In 1984, voters in San Francisco passed Proposition K, which prevents construction of any building over 40 feet (12.2 m) that casts a shadow on a public park, unless the Planning Commission decides the shadow is insignificant. Massachusetts has similar laws against the casting of shadows on Boston Common, the Public Garden, and other important public open spaces. The WELL Building Standard has a feature, Right to Light (F61), that promotes exposure to daylight for 75% of workstations within 25 ft of a window. The European EN 17037 Standard requires certain activities in a building to meet different levels of recommended hours of sunlight exposure (below).


Direct sunlight is a critical factor in the daylight quality of the interior of a building, and it can contribute to the well-being of people. Direct sunlight is generally beneficial for most buildings but can become less meaningful for a hotter climate where the intensity of light overtakes quantity. In some specific building types, like hospitals, schools, or nurseries, where sunlight is highly required for activities, maximum exposure to sunlight should be provided. Direct sunlight is considered valuable for physical health, such as providing vitamin D, which helps build strong bones and healing skin conditions. Patients with access to sunlight recover quicker and have better health outcomes. Direct sunlight is also beneficial for mental health, as during the winter, the days are shorter and the skies are dark, which can increase depression. Taking advantage of the short period of direct sunlight in a day can help stimulate the brain to create more serotonin and reduce excess melatonin.

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