The Struggle for Light and Air in America’s Largest City

You’re looking at a map of all of the shadows produced by thousands of buildings in New York City over the course of one day. This inverted view tells the story of the city’s skyline at the ground level.

From the long westward winter shadows cast on the Hudson from One World Trade ...

One World Trade Center’s average shadow in winter One World Trade Center *Shadow data not available for 3 World Trade Center and 4 World Trade Center One World Trade Center’s average shadow in winter One World Trade Center *Shadow data not available for 3 World Trade Center and 4 World Trade Center

… to the unusually bright, sun-dappled street corners of Midtown Manhattan in spring ...

10th Avenue West 46th St. 9th Avenue West 43rd St. 10th Avenue West 46th St. 9th Avenue West 43nd St.

… to the dark vein of Broadway’s ridgeline ...

West 42nd St. 8th Ave. Broadway Bryant Park 6th Ave. 7th Ave. West 42nd St. 8th Ave. Broadway Bryant Park 7th Ave. 5th Ave.

… to the summertime shadows that form crosses in Madison Square Park ...

East 27th St. East 26th St. Madison Square Park 5th Avenue Broadway East 23rd St. East 27th St. East 26th St. Madison Square Park 5th Avenue Broadway East 23rd St.

… to the interlocking patterns cast by Stuyvesant Town’s towers in the park design.

1st Avenue Stuyvesant Town East 14th St. 1st Avenue Stuyvesant Town East 14th St.

Sunlight and shadow shape the character and rhythm of New York’s public spaces. They have the power to control the flow of foot traffic on our city streets and decide which plazas hum with activity and commerce and which stay barren and desolate. And probably most noticeably, they have the power to change the rent. In most parts of America, sunlight is not debated the way it is in New York, where the city’s thirst for living space, working space and economic growth has turned the sun into a virtual commodity.

So today, on the winter solstice, when the day is shortest and noontime shadows are longest, we used the best technology available to map the building shadows of New York.

Sensitive to the Orientations

A time-lapse view of Madison Square Park. Chang W. Lee/The New York Times

To understand how shadows operate in New York City, it helps to become more conscious of how the city grid is oriented relative to the compass points.

It is said that the sun rises in the east and sets in the west. But at New York’s latitude, that’s not quite the case. On the summer solstice, the sun rises in the northeast and sets in the northwest, while on the winter solstice, the angle changes and the sun rises in the southeast and sets in the southwest. The only times that the sun rises and sets strictly in the east and west are on the equinoxes, when night and day share roughly the same number of minutes.

This means that shadows cast in the winter will be at wildly different angles and lengths than those in the summer. It also means that on the first day of summer, the sun actually sets about 60 degrees to the west of North, which leads to long, curved shadows from the island onto the East River. In the fall, the angle of the shadows on the East River changes as the sun range narrows.

“One of the beauties of Manhattan, particularly in spring or fall, is that the grid is about 30 degrees off true North,” said Michael Kwartler, an architect and a shadow consultant based in New York. “That means the intersections tend to be very bright because the sun is going diagonally across them at lunchtime.”

And these intersections, he said, “tend to be brighter than the streets in between, so it creates this really fabulous rhythm in Midtown of light-dark, light-dark.”

Dark Blocks

A view from 3 Cedar Street, one of the shadiest streets in New York City. Chang W. Lee/The New York Times

On the winter solstice, the sun will shine its rays on New York for just a little over nine hours. But even for those precious hours, huge swaths of Manhattan’s streets will remain in the dark.

This is not an anomaly that occurs on the shortest day of the year, according to new research by Claudio Silva and Harish Doraiswamy, engineers at New York University. They found that, on average, most neighborhoods in Manhattan are covered in shadow for at least half of daylight hours.

One of the shadiest strips in the city is in the financial district, at Cedar Street between Williams and Pearl. It receives no direct sunlight on the winter solstice, the summer solstice or the autumnal equinox. Developers here built the city’s first skyscrapers on plots originally intended for Dutch villagers. The result is a maze of dark narrow corridors formed by tall street walls that block out much of the sky.

William St. John St. Cedar St. Maiden Ln. Pine St. Wall St. Water St. Front St. Pearl St. Beaver St. William St. Cedar St. Wall St. Water St. Front St.

What makes Cedar Street particularly shaded is that it is neatly walled off in the shape of a T, with tall buildings blocking sunlight on the east, west and south.

Bordering the south side of Cedar Street is the old A.I.G. building, now known as 70 Pine. Martin West works at the front desk of the Q&A Hotel, which occupies Floors 3 through 6 of the building. He’s a former resident of sunny Arizona, and the degree of darkness in the area came as a huge shock to him: “You start at 3 p.m. It already feels like the night shift.”

“We would be working inside and just as the sun came out, we’d hop outside to get that one bit of sunlight,” he said. “We even timed it once, and it doesn’t get more than 30 to 40 minutes of sunlight a day.”

Midtown Manhattan in the winter.

The financial district is not the only dark place in the city. Dozens of streets north of 42nd Street in Midtown are also cast in shadow, with some street corners receiving only a few hours of direct sunlight even on the summer solstice. Broadway is notably dark, overtaken by late afternoon shadows and the cascade of overlapping shadows as it cuts diagonally through Midtown.

Yankee Stadium in the winter.

Other parts of the city experience a huge discrepancy of light between summer and winter. One of the largest reversals is found in Bedford–Stuyvesant, in Brooklyn, where bulky, south-facing brownstones on relatively narrow streets cast shadows that last all day when the winter sun is low. The same area is bathed in sunlight in the summer, when the sun is higher in the sky. The same is true of the city’s baseball stadiums, where in the winter, home plate at both Citi Field and Yankee Stadium are covered in shadow most of the day. But fortunately (and most likely by design), they receive a lot of light during baseball season.

Staten Island in the winter.

For a baseline comparison, just look at Staten Island, with its single-family homes and tidy lawns. Shadows rule the north-south streets here for less than a third of the day.

Rules Reveal What We Care About

70 Pine Street, New York City, circa 1940. Andreas Feininger/Getty Images

Light and air have been part of New York’s city planning from the very first days of zoning in the early 20th century. New developments in steel and construction allowed developers to build the city’s first true skyscrapers. Along with those buildings came hand-wringing over the shadows that these structures would cast onto the streets. Perhaps the best-known example is the bulky Equitable Building, constructed in 1915. It boasted an astounding 1.2 million square feet of floor space and rose more than 500 feet, casting a seven-acre shadow.

Back then, both public health officials and city planners saw health benefits in sunlight. Public health officials thought sunlight was an important tool for fighting diseases like diphtheria and tuberculosis. (Sunlight actually is a decent disinfectant, but only for waterborne pathogens).

The city’s first attempt at light preservation was through a setback rule. As successive buildings grew taller, they would have to be continually set back a couple of feet from the street (like the Empire State Building), producing the classic wedding-cake style of skyscraper. Decades later, in the 1960s, the city overhauled this rule in favor of a floor-area ratio model, which tended to produce tall, narrow structures with open plazas at the base (like the Seagram Building).

“In general, zoning regulations show what the city values,” said Luc Wilson, an architect at Kohn Pedersen Fox. “In Shanghai, they care about getting light to the buildings. In New York, they care about protecting light and air in the streets and parks.” England has a Law of Ancient Lights, a common-law doctrine that guarantees a homeowner the right to light if he or she has had access to it for 20 years.

“If a residential window has had access to sky for a number of years,” Mr. Wilson said, “and someone is doing a development that blocks the sky, they actually have to pay for the right to block that sky. There is no rate; the developer just has to negotiate.” While this may sound extreme on this side of the Atlantic, research on the ancient light law suggests that this was actually part of American law until 1838, when it was overruled by an American desire for economic growth and a deference to private ownership.

Our Parks

Central Park in the winter.

In 1987, hundreds of people lined up from Columbus Circle all the way to Fifth Avenue near 68th Street and opened umbrellas in sequence starting at 1:30 p.m. to protest the long shadow that the initial design of Time Warner Center was supposed to cast. Eventually, with a push from Jacqueline Kennedy Onassis, the developers were moved to change the design.

In recent years, the areas around Central Park have revealed the tension that persists between preserving public space and private development in New York City.

Much of the animus is directed toward the tall buildings rising just south of Central Park. Developers are allowed to build buildings “as-of-right,” which essentially means that as long as the proposed building fits within the city’s zoning code, the developer can go ahead and build without public review. So when new buildings on 57th Street were being built, some New Yorkers were worried that they would block out the sun in parts of the park.

These worries aren’t unwarranted. The slender supertalls (whose shadows are included in the interactive map), like 220 Central Park South, the One57 building and the Central Park Tower, do indeed cast very long shadows that reach far into a third of the park. But because the buildings are so thin, these shadows will pass through the park at an incredibly fast pace, like a minute hand on a clock. According to the calculations of Mr. Kwartler, the architect, a tall skinny tower that is roughly 1,000 feet fall will cast a shadow that moves at a rate of 3.5 feet per minute at its most extreme end.

This means that the lasting shadow coverage will be relatively faint. On the winter solstice, the longest edge of the passing shadows cast from these buildings is estimated to last one hour.

To Mr. Kwartler, the real culprits of winter darkness in Central Park are the shorter but more regal buildings on Central Park South, like the Plaza, Ritz-Carlton, Central Park and the Hampshire House. Despite ranging only 200 to 500 feet, these buildings can cast shadows onto Central Park that are several blocks long and that last the entire day.

“People look at shadows as being static and not dynamic,” Mr. Kwartler said. “But they change all the time. It’s really about the duration of the shadow.”

Sunshine activists, like Layla Law-Gisiko, the chairwoman of the Central Park Sunshine Task Force, have no objections to supertalls in principle. But she worries about the impact that these supertalls will have as a whole. “What we have a grave issue with is that there is no vision for 57th Street,” she said. “There has been no opportunity for public review or input.”

But public review is not free; consensus takes time. The as-of-right system helps New York City build fast. The trade-off is that New York sees neighborhoods develop with what Tom Devaney, senior planner at the Municipal Art Society, describes as “a seeming lack of intentionality.”

This ambivalence is apparent in this statement on light from the city’s planning department: “Maximizing light is one among many priorities as we plan for a vibrant, diverse and growing city that addresses the housing and economic needs of its residents.”

But Mr. Kwartler doesn't think the solution needs to be so binary. Sunlight can be saved if developers and planners grow more sensitive to how buildings are oriented. The biggest enemy of parks, and especially small parks near new development in Brooklyn, says Mr. Kwartler, is bulky buildings to the south end of parks. He says that much of the loss of sunlight in our public parks could be avoided if our tall, bulky buildings were simply positioned to the north, west or east side.

“We're animals,” Mr. Kwartler said. “We live in the sun.”

How Did We Calculate the Shadows?

Sunlight and dark shadows at the corner of Sixth Avenue and West 42nd. Chang W. Lee/The New York Times

Calculating the length and shape of a shadow cast from a simple object can be easily done with pen, paper and some basic math. But architects use a more sophisticated method known as ray tracing; it simulates the effects a ray of light can have on a building and its surroundings. Most analyses of shadows study just a few buildings at a time. What made it an interesting problem for the researchers at the Tandon School of Engineering at New York University was how to do it at a scale so you could quickly study whole neighborhoods.

Mr. Silva and Mr. Doraiswamy, two engineers there, worked out a shadow computation that is 10 to 15 times faster than older methods.

How shadows are counted. Claudio Silva and Harish Doraiswamy

To measure shadow coverage, they used a metric known as shadow accumulation, which is simply the total number of minutes that a given point spends in shadow over the course of a day. Point A is darker than Point B because it has been in shadow for one more minute. But Point C will accumulate the same amount of shadow as Point B, because it receives one minute of shadow from both Building 1 and Building 2.