Portsmouth Harbor Light, New Castle New Hampshire

Date added: December 01, 2023 Categories:

Western elevation and setting, looking east (2007)

Initially established in 1771, Portsmouth Harbor Light marks a point of land at the entry to the port of Portsmouth and guides vessels navigating to and from the harbor. This light stations existing structures include a lighthouse built in 1878 atop a lighthouse foundation built in 1804, an oil house built in 1903, and a keepers dwelling originally constructed in 1872. These are typical of a Federal government light station dating from the late nineteenth century to early twentieth century. Through time, the lighted aid to navigation at this location came to be known by a variety of names including Portsmouth Harbor Light, Fort Point Light, New Castle Light, and Fort Constitution Light. Portsmouth Harbor Light has been an operating aid to navigation and landmark along the Piscataqua River in Rockingham County for more than two centuries.

New Castle Island, where Portsmouth Harbor Light is located, is the largest island along the lower Piscataqua River. Originally called Great Island, it was first settled by English colonists in 1623. Accessible only by boat until the nineteenth century, the island's population grew slowly through time. In contrast, a nearby mainland settlement called Piscataqua established in 1630 developed into an important regional center of trade and maritime commerce. It was incorporated in 1653 as the town of Portsmouth. Today, it remains New Hampshire's largest seaport.

Seventeenth-century economic rivalry and military conflict involving the European powers provided impetus for the construction of coastal fortifications at seaports in Britain's North American colonies, including New England. One of these was established in 1632 at Grand Island's northeastern end. Built upon a strategic promontory that came to be known as Fort Point, this position protected the entry to Portsmouth's harbor. Originally built as an earthwork fortification armed with cannon, a timber blockhouse was added in 1666. Further improvements undertaken in 1692 produced a military stronghold that was given the name Fort William and Mary, after the reigning British monarchs. This newly-built "castle" gave rise to the name adopted when the island's settlement incorporated in 1693 as the town of New Castle.

Maritime traffic along the Piscataqua River and in the Portsmouth vicinity increased from the seventeenth century through the eighteenth century. This led to vessels being damaged or lost in the area due to various natural hazards. Around 1721, shipping interests and merchants in the Portsmouth vicinity petitioned the New Hampshire colonial government to establish a light to mark Fort Point and promote maritime safety. This and subsequent attempts to secure public financing for a lighthouse were unsuccessful until the early 1770s when the Royal Governor, John Wentworth, convinced the Provincial Assembly to appropriate funds. In April 1771, Governor Wentworth argued that "Every future expiring cry of (a) drowning mariner upon our coast will bitterly accuse the unfeeling Recusant that wastes life to save a paltry unblessed shilling."

Construction of the first lighthouse at Fort Point was soon undertaken and the light was officially established in July 1771. It became the tenth of 11 lighthouses built in Britain's North American colonies prior to the Revolution. The original light tower was situated approximately 100 yards west of where the existing lighthouse stands today. It was constructed of wood and approximately 50 feet tall. Clad with wooden shingles, this tower supported an iron lantern with a copper roof. Its signal was produced by three oil lamps made of copper. The first lighthouse's official keeper was Fort William and Mary's British commander, Captain John Cochran, whose troops maintained the light in addition to normal garrison duties.

Revolutionary American patriots raided Fort William and Mary's military supplies in December 1774. The British military finally abandoned the fort and nearby lighthouse altogether in August 1775. They were taken over by New Hampshire's revolutionary government. The lighthouse remained intact during the Revolutionary War and provided a daymark for mariners entering or leaving Portsmouth. It is unclear whether it was used as a lighted aid or served only as an observation post for patriot lookouts. The lighthouse was renovated following the end of the Revolutionary War in 1784 and operated as a lighted aid by local authorities.

One of the first pieces of United States congressional legislation to become law under the U.S. Constitution was the Lighthouse Act of 1789. It codified the Federal government's role in establishing and maintaining a nationwide system of lighted aids to navigation. Two years later in 1791, the state of New Hampshire transferred the fortifications and lighthouse at Fort Point to the Federal government. In 1793, President George Washington ordered that a resident keeper be assigned to Portsmouth Harbor Light so that it was maintained at all times.

In the aftermath of the American Revolution, Fort William and Mary became a U.S. Army post named Fort Constitution. Federal funding paid for the fort to be rebuilt and enlarged in 1808. This provided a better defense for Portsmouth Harbor during the War of 1812. A subsequent construction effort from 1860 to 1866 was intended to enlarge and strengthen the early nineteenth-century fortifications. Massive vertical walls built of large granite blocks and cannon ports protected by iron shields were built. However, combat during the American Civil War (1861 to 1865) proved that masonry-walled forts of this type were vulnerable to bombardment from technologically advanced artillery. The fort's reconstruction project was canceled in 1866 when only partially completed, leaving the proposed granite-walled fort unfinished. Fort Constitution remained an active U.S. Army post until the middle twentieth century.

It was deactivated in 1961 and transferred to the state of New Hampshire which now administers it as Fort Constitution State Historical Site.

The Federal government's improvements at Fort Point included the construction of a new lighthouse in 1804. It was built approximately 100 yards east of the 1771 light tower, at the water's edge atop an outcrop called Pollock Rock. The 1804 lighthouse was an 80-foot tall octagonal wooden tower supported by an octagonal masonry foundation. The lantern atop the tower housed a beacon consisting of oil lamps fitted with parabolic reflectors. Lacking any focusing lens, this signal light had a limited visibility range. This situation prevailed for signal lights throughout the United States Lighthouse Establishment during the first half of the nineteenth century.

Meanwhile, in Europe, technological advances led to the production of far superior optical aids to navigation. A French scientist, Augustin Fresnel, developed optics made with glass prisms and lenses that refracted and focused lamp light much more effectively than anything before. Perfected in 1822, a Fresnel lens produced a light signal that could be seen far from shore. This development was a watershed in lighthouse technology.

A classical Fresnel lens resembles a giant glass beehive with a light source in its center. Prisms in the upper and lower parts refract the optic's lamp light, redirecting it to the middle part where a magnifying lens focuses a narrow, intense beam. The light thus emitted is tremendously superior to light produced by previous optics. Fresnel developed a set of seven lens sizes, which are termed orders. The lenses were designated first order, second order, third order, three-and-a-half order, fourth order, fifth order, and sixth order. The first-order lens was the largest and produced the most powerful light. Subsequent numbered orders were less powerful, with the smallest being the sixth-order lens which was suitable for harbor use. The governments of France and Britain began installing Fresnel lenses in their lighthouses during the 1820s and they were used exclusively by 1850.

During the second quarter of the nineteenth century, the United States Lighthouse Establishment was managed by the Treasury Department and directed by auditor Stephen Pleasanton. He had limited appreciation for the advantages of Fresnel lenses and declined to adopt them. Problems arising from Pleasanton's administration led to a comprehensive evaluation of the nation's lighthouse system in 1851. The resulting report revealed that the U.S. was far behind France and Great Britain in lighthouse technology and administration. These findings led to Federal legislation in 1852 that created the U.S. Lighthouse Board. This replaced Pleasanton's authority with a board of directors that included U.S. Army Corps of Engineers and U.S. Navy officers in decision-making positions. The Lighthouse Board represented a permanent administrative change in the construction and operation of U.S. lighthouses. This included implementation of higher standards for lighthouse keepers, more rational selection of sites for navigational aids, and engineering expertise for the design of lighthouses and other aids to navigation. One of the Lighthouse Board's early initiatives was to experiment with the use of Fresnel lenses. The results were clearly favorable and the Board moved to adopt this optical technology as standard lighthouse equipment throughout the country. By 1865, every operating lighthouse in the United States had a Fresnel lens as its optic.

The fuel used for lighthouse lamps in the U.S. also changed through time. During the early nineteenth century, whale oil was standard. However, its cost increased during the middle nineteenth century as whales became scarce. Experiments with other fuels were undertaken. This included rapeseed oil which was the standard fuel used in French lighthouses at this time. However, it was not widely available in the United States. The U.S. Lighthouse Establishment adopted lard oil as a standard fuel in 1883. This was readily available, but it congealed in cold weather and required preheating on a stove in order to be used. The late nineteenth-century development of America's petroleum industry led to the widespread use of kerosene as lamp fuel. This was adopted by the Lighthouse Establishment to replace lard oil. Portsmouth Harbor Light's 1878 lighthouse was the first in the United States where a kerosene-fueled lamp apparatus was installed as original equipment. Another lamp fuel used in late nineteenth-century and early twentieth-century lighted aids to navigation was compressed gas. It was adopted for use in various U.S. Lighthouse Establishment aids including unmanned offshore lights. Around the beginning of the twentieth century, experiments with incandescent oil-vapor (IOV) lamps using pressurized vaporized kerosene and a fiber mantle proved this provided a brighter light than earlier kerosene lamps using the same amount of fuel. As a consequence, IOV lamps came into widespread lighthouse use. This was superseded following World War I by the lighthouse system's adoption of electrical power and incandescent light bulbs. The late twentieth-century, development of light-emitting diode (LED) lamps has resulted in these replacing incandescent bulbs in many Coast Guard aids to navigation.

The Federal government's lighthouse program during the first half of the nineteenth century included construction of a number of light towers at previously unlighted locations. One was Whaleback Light, established in 1830 on Whaleback Ledge. It is situated near the mouth of the Piscataqua River approximately 1.2 miles south of Portsmouth Harbor Light. The position of Whaleback Light made it important as an aid to navigation for vessels approaching Portsmouth from the sea, thus reducing the importance of the lighthouse on Fort Point. Lighthouse engineer Isaiah W. P. Lewis visited Portsmouth Harbor in 1842 as part of a project for improving Federal aids to navigation. Whaleback Light was operating at that time and its importance to local navigation exceeded that of Portsmouth Harbor Light. Lewis recommended reducing the Fort Point light tower's height and the number and size of lamps and reflectors in its lantern. He believed this would reduce its maintenance duties and operating cost. As a consequence, the 1804 light tower was shortened to 55 feet in 1851 and in 1854 the lighthouse's obsolete reflector lamps were replaced with a fourth-order Fresnel lens.

By the early 1870s, the wooden light tower atop Fort Point's Pollock Rock was nearing the end of its serviceable life. The need to replace it with a new tower coincided with late nineteenth-century advances in American engineering concurrent with expansion of the country's industrial capacity. The task of designing a replacement lighthouse was undertaken by the Lighthouse Board Engineer for Maine, New Hampshire, and Massachusetts at that time. This was Lieutenant Colonel James Chatham Duane, U.S. Army Corps of Engineers, who had been Chief Engineer for the Army of the Potomac during the Civil War. From 1868 to 1879, Duane was in charge of military and lighthouse construction in northern New England. He subsequently became Chief of Engineers for the U.S. Army from 1886 to 1888.

Lt. Colonel Duane designed a 48-foot tall tower built of curved cast iron plates that could be bolted together for rapid assembly. The tower's interior included lining with brickwork and a spiral stairway. The contract for casting the new lighthouse's iron plates was awarded to a foundry in Portland, Maine. The parts were transported to Fort Point and in 1878 the cast iron tower was assembled inside the 1804 wooden tower. When the new tower was completed, its wooden predecessor was dismantled.

In 1896 an addition was built next to the cast iron tower on the southeastern side. It was a small, flat-roofed, one-story shed used to house the operating machinery for a bronze fog bell. This bell was mounted atop the shed's roof and in foggy weather was struck with a single blow every ten minutes. The fog signal shed was removed when the fog bell was replaced with an automated electrical fog signal. The bronze fog bell is presently on display in front of the main building at the U.S. Coast Guard's Portsmouth Harbor Station.

By the middle nineteenth century, the keeper of Portsmouth Harbor Light occupied a dwelling located on Fort Point west of Fort Constitution. This dwelling was situated near the Walbach Tower, a circular masonry fortification built in 1814 to defend the fort's inland approaches. By circa 1870, the Lighthouse Board determined that a replacement dwelling was needed, and a new one was constructed in 1872 atop the previous building's foundation. The new dwelling was a rectangular, one-and-one-half-story wood frame structure with clapboard siding and a hipped gable roof. Its design followed customary regional standards for middle-class single-family residences in coastal New Hampshire.

A construction project in 1897 for a new artillery emplacement (Battery Farnsworth) west of Fort Constitution made it necessary to move the keepers dwelling approximately 200 feet eastward. A late construction project in 1906 for Battery Hackleman led to the dwelling being moved from there to its existing position inside Fort Constitution's unfinished granite wall. Around the same time, an opening was made in the fort's southern wall for an elevated walkway. This provided for access from the dwelling to the light tower.

An oil house for storing lamp fuel was constructed during the late nineteenth century near the light tower. It was replaced in 1903 when a brick masonry oil house was constructed approximately 70 feet west of the lighthouse. This new structure was resistant to fire and well-suited for storing highly flammable kerosene. It remains today.

The Lighthouse Board was abolished in 1910 when a Federal law created the U.S. Lighthouse Bureau, an agency of the Department of Commerce. The newly established bureau soon undertook measures to improve the facilities and operation of the nation's Lighthouse Service. In 1939 the Lighthouse Bureau was incorporated into the U.S. Coast Guard and ceased to exist as a separate agency.

Today, the lighthouse and oil house at Portsmouth Harbor Light remain in their original positions. Though it has been moved twice since 1872, the keeper's dwelling was placed in its present position in 1906. Over time its location has become historically associated with the nearby related light station buildings. The lighthouse continues to fulfill its original role of aiding mariners by marking the tip of Fort Point at the entry to Portsmouth Harbor and remains a prominent aid to navigation in the area. It is recognized in the coastal New Hampshire area as an important landmark.

The Coast Guard has leased the property's lighthouse and oil house to the Friends of Portsmouth Lighthouse, a non-profit organization affiliated with the American Lighthouse Foundation. The Friends of Portsmouth Lighthouse maintains the lighthouse, oil house and elevated walkway, and provides for public visitation regularly.

Site Description

Portsmouth Harbor Light was established in 1771 and marks the entry to the port of Portsmouth, New Hampshire's only deepwater port. It is located in the town of New Castle on the western shore of the Piscataqua River at the northeastern end of New Castle Island, Rockingham County. This property includes a lighthouse and oil house standing on rocky terrain adjoining Fort Constitution State Historical Park, and a keepers dwelling located on the inner side of the fort's southern wall. There is also an elevated walkway extending from the fort's wall to the light tower. Built in 1878, the lighthouse is a cast iron conical tower approximately 48 feet tall that supports a 10-sided lantern. It stands atop an octagonal masonry foundation built in 1804 for a preceding light tower. The tower is painted white and the lantern and lantern gallery are black. The oil house was built in 1903 for storing lamp fuel. It is a one-story, one-room brick building with a gable roof. The keepers dwelling is a one-and-one-half-story wood frame building painted white. It is supported by a granite masonry foundation. This building was originally constructed in 1871 approximately 0.1 mile to the west, was moved in 1897, and moved again in 1906 to its present location. The elevated walkway was built in 2006 and is the latest in a series of similar walkways built since Portsmouth Harbor Light was established. This property is owned by the U. S. Coast Guard. It is an active Federal aid to navigation identified as number 8330 in the regional light list. The lighthouse's optic is a fourth-order Fresnel lens inside a green acrylic cover. It signals a fixed green light visible for 12 miles in clear weather. A modern fog signal mounted on the lighthouse's lantern gallery sounds a one-second blast every 10 seconds. Portsmouth Harbor Light is accessible overland by way of Fort Constitution State Historical Park.

Portsmouth Harbor Light occupies less than one acre in the town of New Castle, Rockingham County, New Hampshire. Its location is approximately 2.5 miles east of the city of Portsmouth. Situated on the Piscataqua River shoreline at the northeastern corner of New Castle Island, this property's setting is the southeastern tip of the Fort Point peninsula. Fort Point is at the south side of the mouth of Portsmouth Harbor where vessels navigating from the sea along the Piscataqua River must turn westward to enter the harbor. Portsmouth Harbor Light is a prominent landmark at the entry to the port.

Fort Point is largely occupied by Fort Constitution State Historical Park and U.S. Coast Guard Station Portsmouth Harbor. The property is part of the Coast Guard Station. Portsmouth Harbor Light's oil house, elevated walkway and lighthouse stand upon rocky terrain adjoining the exterior of Fort Constitution's southeastern corner. The property's keepers dwelling is located inside Fort Constitution's southern wall at the end of a driveway extending eastward from the main Coast Guard Station. A gap in the fort's southern wall provides access to the elevated wooden walkway leading to the oil house and the lighthouse, which is approximately 100 feet south of the dwelling.

The lighthouse stands atop bedrock next to the Piscataqua River, just above the high tide level. It includes a foundation, tower, and lantern. The tower is painted white. The lantern and gallery atop the tower are painted black.

The foundation is octagonal and built of rock masonry capped with a concrete slab. It was originally constructed in 1804 to support an octagonal lighthouse built of wood that was wider than the existing light tower. The wooden structure was replaced in 1878 by the lighthouse, which sits centered atop its predecessor's foundation. This foundation varies in height from approximately 2 feet to 5.5 feet because of the irregular surface of the bedrock below. The foundation is approximately 30 feet in diameter with a circumference of approximately 125 feet. Each side tapers inward from base to top. A collar of eight wooden timbers surrounds the perimeter of the foundation's concrete slab. These are fastened at their joints with bolted metal plates and supported by brackets fastened to each of the foundation's eight corners.

The light tower is conical and approximately 48 feet tall. It is approximately 14 feet in diameter at the base with a circumference of 47 feet, 3 inches. The tower is built with six tiers of 12 cast iron plates each. These are fastened with bolts and nuts. The iron plates in the lower four tiers measure approximately 8 feet tall by nearly 4 feet wide. The upper two tiers enclose the lighthouse's watch room and are each approximately 4 feet tall. The tower's entry is on the western side at the base, level with the foundation's concrete slab. This is a simple doorway rounded at the top with a segmented arch. It is approximately 6.5 feet tall by 2.8 feet wide with a wooden jamb. The door is made with wooden planks oriented vertically. Its hardware includes two iron strap hinges on the left side, and a small metal handle below a hasp secured with a padlock. The door is painted white with black hinges. It opens outward.

The tower is pierced with three segmental arch windows framed with an exterior decorative cast iron surround that includes a projecting sill and Italianate hood with a triangular pediment. These light the interior spiral stairway and are placed in offset ascending order, one in each of the three tiers above the lowest one. The second tier window is oriented east and the four tier window looks northwest. The fourth-tier window is on the south side. The windows' interior frames are made with wood and hold wood sash with 2-over-2 lights, rounded at the top. There are four circular port lights at the seam joining the fifth and sixth tiers of cast iron plates, just below the lantern gallery. These are approximately 15 inches in diameter and light the lighthouse's watch room. The port lights are evenly spaced and oriented towards the cardinal directions.

The tower supports a circular platform approximately 15 feet in diameter made with cast iron plates. Twelve evenly-spaced cast iron brackets attached to the tower's exterior support the platform's overhang. They are painted black. This platform supports the lighthouse's lantern and lantern gallery. The gallery is surrounded by an iron railing supported by decorated cast iron stanchions capped with ornamental finials. The stanchions support an upper flat rail and a lower rod railing. The lantern sits centered atop the platform and includes a circular parapet wall made of iron that is approximately three feet tall. An iron door with strap hinges and latch pierces the parapet wall's western side and provides access from inside the lantern to the gallery. The glazing above the lantern's parapet includes 10 rectangular frames approximately 3.5 feet tall holding 10 glass storm panes measuring 26 inches by 35 inches each.

The lantern's metal roof springs from a soffit above the glazing. It is made with ten triangular segments that rise to meet at an apex topped with a cast iron ventilation ball capped with a bronze lightning rod. A modern fog signal is mounted on the gallery's eastern side. It sounds a one-second blast every ten seconds.

The light tower's interior is lined with unpainted red brick masonry approximately one foot thick. An air space separates the tower's cast iron exterior from the brickwork lining. The interior floor on the ground level is 11 feet in diameter and is also made with red brick. A 43-step cast iron spiral stairway rises counter-clockwise from ground level to the watch room. It is painted gray. The iron stair treads are cast with a diamond-pattern surface and are anchored at the outer edge of the tower's brick lining. The space beneath each stairway tread is open. A curving iron handrail follows the stairway's inner edge, supported at each tread by a narrow iron baluster.

The spiral stairway ends at a four-panel wooden door providing access to the watch room. This circular room is partially lined with vertical beadboard paneling and the remainder is metal. The wall is painted white. A curved partition separates the room from the upper part of the spiral stairway. A 5-shelf closet is built into the partition. It has a wooden door made with bead board. The closet is used to store maintenance supplies and equipment. The watch room's floor is made with ten triangular iron plates. Its surface and underside are painted gray. The ceiling is made with radial narrow wooden slats that converge to a central circular decorative molding. The watch room is lighted with four circular port-light windows. Two retain original nautical port lights with bronze hardware. The other two windows have fixed glass panes. A curving, steep iron stairway rises from the watch room floor to an opening in the ceiling, providing access to the lantern room. It is painted gray. The stairway's seven treads are attached at the outer edge to the watch room wall. A wooden trapdoor at the top opens upward into the lantern room.

The lantern room's 3.5-foot tall circular parapet wall is lined with vertical bead board painted white. The metal floor is painted gray. The parapet wall is pierced with five circular brass air vents. These are 8 inches in diameter and placed below every other side of the lantern's ten-sided glazing. The lantern's optic is supported by a 3-foot, 4-inch tall hollow cast iron pedestal measuring 5.5 inches in diameter and flaring at the top and bottom. This is attached to the center of the lantern room floor. The optic is a stationary fourth-order Fresnel lens manufactured by Henri LePaute of France and marked with United States Lighthouse Service number 4177. Its focal height is 52 feet above mean high water. The light source is an incandescent electric bulb. This Fresnel lens is covered with a green-colored acrylic cylinder supported at the base by aluminum rods. This provides a fixed green signal visible for 12 miles in clear weather.

The property's oil house was built in 1903 to store lamp fuel for the lighthouse optic. It replaced an earlier structure. This building is situated approximately three feet from Fort Constitution's southern wall and approximately 70 feet northwest of the lighthouse. It stands atop rocky terrain with a gravel surface. A stairway attached to the property's elevated walkway approximately 15 feet outside Fort Constitution's southern wall provides access.

The oil house is rectangular, one story tall, and approximately 10 feet wide by 11 feet long. It is built of brick laid in stretcher courses. The oil house has a gable roof oriented east-west along the building's long axis. Its entry is a doorway below the western gable that is fitted with a wooden jamb and a four-panel door painted white. The gable woodwork is painted white and includes boxed cornices with returns. The roof's side eaves project slightly along the side walls and are also painted white. The roof is clad with gray slate shingles. The walls of the gable ends are pierced near the top center with narrow, rectangular ventilation openings fitted with slatted wooden vents painted white. The building's single room has a floor made of red bricks. The interior brickwork walls had been painted white in the past, but this has deteriorated. Overhead, exposed wooden rafters support the roof.

This building was renovated in 2004 by the Campbell Construction Company of Beverly, Massachusetts. The work included replacing several roof shingles and repairing a roof leak. Other work included refurbishing and repainting the wood trim along the roof eaves and doorway on the building's exterior, installing a new door and cleaning the interior.

The keeper's dwelling was built in 1872 from plans provided by James C. Duane, First Lighthouse District Engineer. It is a one-and-a-half-story wood frame building approximately 35 feet long by 30 feet wide with a gable roof. The dwelling's long axis is oriented east-west with the front facade facing south. It has clapboard siding that is painted white, and green trim around the windows and roof eaves. The roof's east and west end gables are hipped. There is a hipped cross-gable centrally located on the roof's south side, and a centrally-located gable-roofed dormer on the north side. The roof is clad with red asphalt shingles. The dwelling's fenestration consists of wood-framed, 6-over-6, double-hung sash. Access to this building is overland from the Town of New Castle by way of the Coast Guard Station. The keeper's dwelling is currently used by the U.S. Coast Guard and the National Marine Fisheries Service for office space.

When originally erected, this building sat atop the foundation of a predecessor keepers dwelling approximately 850 feet west of its present-day position. This original location was on the south side of an early nineteenth-century brick circular fortification called the Walbach Tower. Construction of an artillery battery during the late nineteenth century led to the keepers' dwelling being moved approximately 550 feet eastward in 1897. Additional military construction led to the dwelling being relocated again in 1906 when it was moved approximately 300 feet eastward to where it now stands within the walls of Fort Constitution.

The dwelling's 1906 move included the construction of a foundation to support the building. This foundation is made with massive rectangular granite blocks of the type used in the never-completed 1860s reconstruction of Fort Constitution. The granite masonry foundation rises to 6 feet, 8 inches above ground level, and encloses the building's basement. A doorway in its western wall provides access to the basement.

The dwelling's first story is divided into three bays along the south-facing front facade. The middle bay includes a centered entry porch supported by non-original columns made of concrete block and brick. The porch includes wooden columns supporting a hipped roof and a wooden balustrade. On the porch's western side alongside the building, a 10-step wooden stairway with a simple wooden handrail rises from ground level to the porch. This stairway is parallel to the south front of the dwelling and is a replacement. The front porch provides cover for the dwelling's main entry which is fitted with a single leaf four-panel wooden door that is painted green. The first-story facade on either side of the entry is pierced with one window on the east and one on the west. The roof's hipped cross gable encloses an upper half-story room and extends outward above the entry porch. The clapboard facade beneath this gable is pierced with a 6-over-6, double-hung window with green-painted wood trim.

The dwelling's eastern and western gable ends are both pierced with four windows fitted with 6-over-6, double-hung sash. The two upper half-story windows are offset nearer one another than the two first-story windows. A brick chimney pierces the roof above the eastern gable.

The dwelling's northern facade includes an enclosed vestibule positioned at the first story's middle bay. This provides for access at the building's rear. The vestibule has a shed roof and is supported by three wooden posts. A wooden stairway on the western side is parallel to the dwelling's north side with its foot at the building's northwest corner. This stairway includes a handrail and a small landing at the top next to the vestibule doorway.

The vestibule includes a window on its northern side fitted with a 6-over-6, double-hung sash. The bays to either side of the central vestibule include a single window on the east and one on the west. These are both fitted with 6-over-6, double-hung sash.

Above the vestibule, a simple gable roof dormer has been added. Its roof is not clipped. The clapboard wall beneath the gable is pierced with a doorway that opens onto a rectangular wooden platform affixed to the vestibule roof. A metal fire escape ladder attached to the vestibule's eastern side extends from this platform to ground level.

An elevated walkway provides access to the lighthouse from Fort Constitution. It is approximately 80 feet long and crosses low-lying terrain potentially awash during times of high water. This walkway was built in 2006 by the Ricci Construction Company of Portsmouth, New Hampshire, with funding provided by the Friends of Portsmouth Lighthouse. This is the latest in a series since the first elevated walkway was constructed in 1804. Over the years, a successor has been built as each predecessor became unserviceable.

The walkway's northern end is a set of steps approximately 25 feet south of the keeper's dwelling. These steps rise from the inner side of the fort's southern wall to the walkway deck. The walkway passes through an opening in the wall and extends southward approximately 50 feet to where it makes a southeast dog-leg turn and continues approximately 30 feet to the lighthouse's masonry foundation. A set of steps on the walkway's western side approximately 10 feet south of the fort's wall provides access to the oil house.

Three pyramidal rectangular piers support the walkway outside the fort's wall. These rest atop the rocky terrain and are approximately five feet tall. The northern one nearest the fort is rock masonry. The next has rock masonry in its lower part and a concrete upper section. The southern pier is most exposed to wave action and is made of concrete. The three piers support stringers atop which the walkway's plank decking is attached. These planks are Trex, a modern recycled wood and plastic composite material that resists deterioration. Rectangular, pressure-treated wood stanchions are affixed at even intervals to stringers along the deck's edges. The stanchions support railings along both sides of the walkway. Each side has three pressure-treated wood railings attached to the stanchions at the top, middle and near the bottom. The walkway's deck is gray. The railings are painted white.

Today's Portsmouth Harbor Light is the third aid to navigation structure in this vicinity since the original beacon was constructed nearby in 1771. The second lighthouse was built in 1804 and occupied the same location as the one built in 1878 that stands today. The existing lighthouse remains essentially unaltered from its original construction, and its location, structural character and setting are unchanged. Modifications that have been made relate largely to paint color and updates to operational equipment. The existing light tower was originally painted brown. It was repainted white in the early twentieth century. This white tower and black lantern coloration is the lighthouse's official daymark recorded in the Coast Guard's regional light list.

The lighthouse's original optic was a fourth-order Fresnel lens manufactured in France by L. Sautter and Company. This signaled a fixed white light from 1878 to 1911 when the characteristic was changed to a fixed red. light. The coloration was provided by red glass screens that surrounded the beacon. The optic's characteristic was changed back to a fixed white light in 1932, and then to a fixed green light in 1934. It remains fixed green today.

The 1878 lighthouse's optic was lighted with a kerosene lamp when it was initially established as an aid to navigation. It was the first lighthouse in the United States where a kerosene-fueled lamp apparatus was used as original equipment. The original lamp was changed out in 1911 and replaced with an incandescent oil-vapor (IOV) lamp. The IOV lamp provided a brighter light while using the same amount of fuel as the earlier kerosene lamp. In 1932 the beacon's characteristic was changed from a fixed red light to a fixed white light. In 1934 the lighthouse was electrified and a green incandescent bulb was installed, changing the lighthouse's characteristic to signal a continuous green light. The original Sautter & Co. optic remained in use until after 1935. It was eventually changed out for a replacement fourth-order Fresnel lens manufactured by Henri LePaute of Paris. The lighthouse's present-day characteristic remains a fixed green signal and is provided using a green acrylic cylinder that covers the Fresnel lens. Portsmouth Harbor Light was automated in 1960.

The lighthouse's fog signal during the early and middle twentieth century was a mechanically operated fog bell mounted atop a pyramidal platform resting on the foundation alongside the light tower. This was replaced during the late twentieth century with a modern automated electrical fog signal. The existing fog signal is mounted on the lantern gallery atop the light tower.