The team leveraged its expertise in building user-friendly tools and data visualizations, creating GIFs and images that depict these metrics in various conditions to help MAS assess the relative well-being of NYC residents. The work culminated in April 2021 when MAS released a policy brief, “A Framework for a City Built for Sunlight,” with recommendations aimed to help city officials reshape the public realm with a deeper understanding of sunlight’s importance in the city’s public spaces.

Access to direct and diffused daylight in open spaces has a direct impact on our physical and mental health. It also impacts our enjoyment of the public realm and even the local economy through our use of local businesses. This is especially true during winter months, when lower sun angles and shorter days reduce light availability in urban areas, contributing to low vitamin D levels, sleep disorders, and seasonal affective disorder (SAD).

The simulation of daylight access was developed using a 3D model of existing buildings based on NYC Department of City Planning’s (DCP) data. Average light reflectance values for streets, landscapes, and building materials were assumed for the model. Local sky conditions, regarding direct, and diffuse illuminance, were modeled using Typical Meteorological Year, version 3 (TMY3) data for NYC Central Park as made available by the US Department of Education (DOE). From there, hourly illuminance values were modeled using a radiance-based raytracing engine to calculate the amount of direct, diffuse, and reflected light at the street level.

The team conducted an analysis for the three months with the lowest available illuminance levels in NYC: November, December, and January. Assuming a minimum illuminance target for a “well daylit” open space of 10,000 lux, the percentage of hours where that target is met was calculated for each part of the day (morning/noon/evening). Whenever an area showed adequate daylight for more than half of the hours in a part of the day, it was considered daylit during that part of the day. Finally, open spaces were classified accordingly to identify areas with only partial access.

East Midtown had the least amount of daylight by far with almost 80% of the neighborhood never reaching the required light levels. St. George had the most total daylight, only failing to receive adequate daylight 5% of the time.

The amount of solar radiation we receive is only one of several environmental factors that affect our thermal experience (including temperature, humidity, and wind speed), and this is strongly determined by the built environment. Direct sunlight on our body can help us stay comfortable during the shortened days of winter, but also can be the source of overheating in summer. Overall, the appropriate control through shade or lack thereof can increase comfortable hours outdoors in NYC by 40–50% throughout the year.

The simulation of sun hours was developed using a 3D model of existing buildings based on NYC DCP’s data, and solar altitude and azimuth information for NYC’s latitude. The evaluation of solar benefit and harm was developed by calculating the UTCI effective temperature for every hour of the year, with and without direct solar access, but keeping all other parameters equal. The team calculated UTCI temperatures using TMY3 data for NYC Central Park as made available by the U.S. DOE for each hour of the year. Wind speeds at street level were estimated as the monthly average for that hour in NYC, considering the average urban density of the neighborhood (hence ignoring local wind patterns caused by existing buildings).

For the study, comfort was assumed between UTCI effective values of 57 and 82 F (including the effect of temperature, humidity, wind, and solar radiation). Beneficial sun was then defined for any hour where its presence would bring UTCI values into comfort, and harmful sun for any hour where its presence would bring UTCI out of it. Finally, harmful and beneficial sun hours were averaged by season and mapped to identify sensitive areas in each case.

Using a sun path for New York city and existing buildings (from NYC DCP 3D model) as obstructions, the number of direct-sun hours per day was calculated for a single day per week for the study’s growing season (April 1 to October 31). These results—binned to the percentage of weeks that receive at least six (full sun) and at least three (partial sun) hours of direct sunlight per day—are shown in the maps provided.

A map of the existing tree canopy was overlaid. Locations were considered “at-risk” when the existing canopy received full or partial sun 50% or less of the weeks in the growing season.

A map of existing parks, plazas, and other public spaces was overlaid. Locations in which these areas had over 90% of weeks in the growing season with full or partial sun were considered “areas of opportunity” for new tree planting.

As stated above, access to sunlight and the outdoors impact our well-being, including our sleep, mood, and activity level, among other factors. Access to sunlight, the outdoors, and properly shaded public spaces are also not equally available to all depending on where you live. Underserved communities often have fewer parks (or parks that are less well-maintained) in their neighborhoods, which are often even hotter in temperature than those of their wealthy counterparts.

The impacts expand beyond our personal wellbeing to include neighborhood economies. Businesses can capitalize on outdoor space for seating in both warm and cold months when they have access to shade and sunlight (respectively). This can be met through the inclusion of more parks (and therefore fewer blocks dedicated to only buildings) and trees. These factors become a positive feedback loop with either growing benefits or consequences depending on how the public realm is managed.

Visible in the findings from KPF’s team, East Midtown, the city’s central business district, is the region that most lacks access to sunlight, which reduces harmful exposure in the summer, but also reduces beneficial exposure in the winter. Midtown also lacks green space compared to the other four areas studied. In the neighborhoods where there is such little access to green space and tree canopies, it is crucial to protect what does exist. In places that have the space and access, the question becomes, how do we utilize these amenities? These issues often fall on the communities themselves to push for the protection and utilization of these spaces. MAS has been pushing for this responsibility to exist at the city level.