PH 3/2 vs PH 3½-2½ Table Lamp: Which Size Fits Where

Two of Poul Henningsen's table lamps for Louis Poulsen share the same three shade geometry and almost the same profile, yet one stands 45 mm wider than the other. That gap, and a considerable difference in weight, is what decides which lamp belongs on a bedside table and which on a sideboard. Here is how the PH 3/2 and the PH 3½-2½ compare, using only the figures given for each version.

What the numbers in a PH name mean

PH names are measurements rather than model codes. The first figure gives the size of the top shade in decimetres, the second the size of the middle shade. A PH 3/2 therefore sets a three decimetre top shade above a two decimetre middle shade, and a PH 3½-2½ adds half a decimetre to each. Read that way, the name describes the proportions of the shade set before you have even seen the lamp.

The system behind both is older than either design. Henningsen developed the three shade System PH with Louis Poulsen in 1926, a year after the Paris lamp he made with the company won gold at the Exposition Internationale des Arts Décoratifs. Every shade curve follows a logarithmic spiral, and the three shades are stacked in calculated positions so that light from a single bulb is redirected downwards and none of it reaches the eye directly. The reasoning is set out in more detail in how the PH three shade system works.

Four versions, side by side

Both sizes stay in production in more than one material, so the real choice is between four table lamps rather than two. Everything in the table below is taken from the specification of each version.

Designer for all four: Poul Henningsen. The glass and metal PH 3½-2½ table lamps both go back to his 1928 drawing.

What the extra 45 mm changes on a desk

Height is almost identical, 455 mm against 465 mm, so the two lamps read as the same object across a room. The difference is width. At 285 mm the PH 3/2 Table Lamp clears a shallow bedside table and leaves room beside a laptop; at 330 mm the PH 3½-2½ Table Lamp wants a surface with some depth behind it, or it will overhang the front edge of a narrow console.

Those 45 mm also change the light. A wider top shade throws its pool further across the surface below and carries the shade edge a little further from a seated eye line, which is why the larger lamp reads as the more social of the two: it lights a stretch of sideboard rather than a book. The smaller one concentrates the same glare-free light into a tighter island, exactly what Henningsen wanted beside a chair.

Weight tells the same story from another direction. The white opal PH 3/2 is 2.5 kg, light enough to move between rooms without thinking about it. The PH 3½-2½ in glass is 6.6 kg, the metal version 5.6 kg and the aged brass PH 3/2 5.3 kg. Those are lamps you place once, which is worth knowing if you like to rearrange a room in the evening.

Glass top shade or spun aluminium

Within the larger size there is a second decision. The all-glass PH 3½-2½ glows as a whole object: the top shade is lit from inside along with the two below it, so the lamp becomes a soft point of interest from across the room as well as a working light. It is the version to choose if the lamp has to carry the evening atmosphere of a sitting room.

The PH 3½-2½ Metal Table Lamp swaps that top shade for spun aluminium with a white rolled edge and a white interior, keeping mouth-blown glass for the two lower shades. Because the top shade is opaque, almost all of the output goes down onto the surface and the glow stays contained. It also carries the period details collectors look for: Henningsen's original shade holder, the small adjustment screws, and a frame in silk-matt brown brass that nods to early burnished fittings. In white it disappears into a pale room; in red, yellow or green it becomes the one piece of colour on a desk.

Finishes, and how to choose

The smaller size is the more adaptable of the two on colour. The PH 3/2 Table Lamp comes in seven finishes: brass metallised, high lustre chrome plated, black metallised, and four glossy colours in beige, burgundy, deep blue and deep green. The larger glass lamp keeps to three metal finishes, chrome, black metallised and brass metallised, which suits its role as a quieter, more architectural object.

The PH 3/2 Aged Brass Opal Table Lamp is the outlier. Same 285 x 455 x 285 mm shell, but 5.3 kg, with an aged brass top plate and stem lacquered to hold the finish, a 2.5 m black textile cord and a through-switch. Its three-layer opal glass is glossy outside and sandblasted inside, so the shades glow evenly while most of the light still goes down onto the table.

A short way to decide:

• Shallow bedside table, small flat, or a lamp you expect to move: the PH 3/2 in white opal, at 285 mm and 2.5 kg.
• Sideboard or console that has to light a whole corner in the evening: the PH 3½-2½ in glass, at 330 mm.
• Desk or hallway where light should stay on the surface: the PH 3½-2½ Metal, with its aluminium top shade in white, red, yellow or green.
• A room of dark wood and warm metal: the PH 3/2 in aged brass.

Whichever way the measurements point, both lamps do the same job in the same way, and both have stayed in production for close to a century because the geometry still works. If you are still weighing up heights and footprints, the Table Lamps collection is the place to compare them against the rest of the room.