On the night of 12 February 1899, disaster struck Chicago. Fire swept through the celebrated bookstore of McClurg & Co, home to an irreplaceable collection of rare volumes and a favourite haunt of local writers. Firemen arrived to find flames shooting into the sky – and the water hydrants frozen. Helpless, they watched as floors and walls collapsed sending broken glass and red-hot bricks crashing into the street. The cause of the conflagration? An explosion of gas from a leaking pipe. Remarkably, some newly installed windows survived intact. If gaslights had destroyed a historic building, these panes represented the future. Made from Luxfer prisms, they were an audacious “daylighting” technology that challenged both hazardous gaslights and newfangled and expensive electric bulbs.
MODERN facades on Victorian buildings in Chicago and other industrial cities of the American Midwest often hide a secret. Scattered through old drugstores and boarded-up banks from Madison to Fort Wayne, curiously shaped glass tiles known as Luxfer prisms lie just a few centimetres behind the paint and plaster. Luxfers were one of the 19th century’s greatest innovations in lighting, and an idea that is beginning to make a comeback in our own energy-conscious times.
By the 1880s, rapidly expanding commercial buildings in Chicago faced a vexing problem: how could they keep their spacious interiors well lit? Plate-glass store fronts admitted light only so far, and windows on narrow side streets were shaded by newly ascendant high-rises. Artificial lighting remained imperfect: gaslight was dangerous and uncomfortably warm in the summer, and electric lighting was expensive and not yet widespread. Urban interiors were becoming so gloomy that one exasperated Chicago landlady complained that her dining hall was “so dark at times during the day that persons passing through it were in danger of knocking articles off the dining room table”.
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Enter James Pennycuick, a British inventor who had set up shop in the US to manufacture glass electrical insulators. Pennycuick soon found himself pondering the qualities of the glass in those unsatisfactory shop windows. Since the 1840s, architects had used “vault lights” – grids of glass tiles embedded into the street above to direct light into basements. Even earlier, shipbuilders had hit on the notion of fitting “deck prisms” to scatter light safely across flammable cargoes in a ship’s hold. These ideas relied on horizontal lenses facing up into direct sunlight. The question for Pennycuick was whether a vertical sheet of glass could also capture and throw light into the dark recesses of stores.
He thought prisms might do the trick. What if there were a series of prisms on the interior of windows, carefully angled to refract the wasted sunlight away from the front of the store and into those dimly lit corners? You wouldn’t need to redirect an entire window’s worth, just the light entering the top portion of the pane. Poorly lit buildings could make even more of the available light by fitting two sets of prisms, one at the top of the window and another in a canopy projecting from the building to catch light from above and direct it through the prismatic window.
In 1882, Pennycuick patented his concept of a “prismatic light”, but more than a decade passed before Chicago inventor William Winslow came up with a practical way of bonding a series of small prismatic tiles together to form a decent-sized window. was simple: surround each prism with a thin strip of copper and lower into an electrolytic bath. The glass and metal fused together to create a strong, rigid panel.
With prismatic windows now a practical proposition, Pennycuick and a group of Chicago investors established . The firm retained two professors from nearby Northwestern University to determine the best way to position the prisms. Architects were invited to submit prism-friendly building designs, and a young Frank Lloyd Wright was hired to design ornamental exteriors for the tiles.
Flush with money from Chicago’s captains of industry, in 1897 the Luxfer Prism Company unveiled its glittering answer to dingy stores and gloomy offices: 10-centimetre squares of prismatic glass that could be arranged in grids across the tops of windows or on the hinged transom windows used for ventilation. The results were so dramatic that in many rooms gas and electric lights could be turned off altogether during daylight hours.
“In many rooms the lights could now be turned off altogether”
“Stop wasting daylight,” proclaimed newspaper ads. “Daylight your store… dispense with artificial light. Daylight costs nothing.” True enough: sunlight was free. Luxfer prisms, however, were most assuredly not. “Lucical engineers” had been trained to customise panes for maximum sunlight, and custom-fitting and electro-glazing a single room could cost as much as $200. Major installations cost thousands, and architect Louis Sullivan’s massive Carson Pirie Scott department store in Chicago had a staggering $40,000 worth.
Despite their cost, many customers reported savings that repaid their investment in two or three years: the summer lighting bill at Chicago’s Orr & Lockett hardware store, for instance, dropped from $360 to $132. Princeton University adopted Luxfers for its new library, as did the Canadian Pacific Railway for its Montreal terminal. US meat-packing giant Armour was delighted with Luxfers, declaring them “one of the great inventions of this very practical era in which economy is the watchword”. It also helped that electro-glazing made Luxfers remarkably resilient in fires. When Chicago’s famous bookstore McClurg & Co was rebuilt, its windows sparkled with prisms. By 1906, the Luxfer Prism Company boasted 12,000 installations across the country. Shopping streets were transformed, often presenting a uniform frontage of glittering prismatic glass transoms and canopies.
A sure sign of Luxfer’s success was its numerous legal battles with imitators. Some rival innovations were genuinely promising: in 1898, for instance, West Virginia inventor Frank Wadsworth suggested cutting notches into ordinary window glass and sandwiching two panes together to create an internal deflector. Despite promising cheaper production and easier maintenance, internal deflecting panes were never competitive because the notches caused the glass to fracture.
Luxfer branches opened worldwide, most notably in London and Berlin, culminating in 1924 in an immense prismatic rooftop for De Bijenkorf, the Dutch department store in the Hague. Luxfer also revisited the idea of glass vault lights, designing vertical “lucidux” panels to redistribute light falling on the ground more evenly through basements.
But not everyone was enthusiastic about the trend for “daylighting”. The rise of the Luxfer prism coincided with a period when many American architects looked to ancient Greece and Rome for their inspiration. These “Beaux Arts” architects “just hated Luxfer prisms”, recalled architect William Gray Purcell, a young upstart in Frank Lloyd Wright’s Prairie School movement. “The Greeks hadn’t had Luxfer prisms and the Romans hadn’t had Luxfer prisms. So how could you put them in a building without destroying your prestige?”
The traditionalists’ fears were well founded. Luxfer prisms brought with them a new aesthetic: daylight couldn’t penetrate walls, so designers were encouraged to adopt open-plan interiors or low glass partitions. To maximise reflective surfaces, Luxfer also recommended lighter and brighter colours. Out went the heavy draperies, the dark wood, and the rich red walls of the Victorian era, and in came the bright, sunny palette of Modernism.
Yet by the 1930s Luxfers themselves were looking old-fashioned, thanks to cheap and widespread electrification. The glare of glittering transoms became superfluous, even a nuisance. Old Luxfers are now often found boarded up or under layers of thick black paint. With the rise of central air conditioning, their burial became complete: the drop-ceilings used to accommodate ductwork often covered up Luxfer windows and transoms.
Luxfers can still be found in neglected buildings in the rust belt towns of the Midwest, though manganese used in early glass manufacturing has caused many panes to darken to an attractive if impractical shade of violet. Restoration efforts in such cities as Madison, Wisconsin, are bringing old transoms and store fronts to life again, and Wright’s ornamental Luxfer patterns are finding an unexpected second life in the stencilling of everything from cabinet fronts to night lights.
Green building practices and steeply rising energy costs have revived interest in “daylighting”. Siemens and 3M have developed prismatic film and injection-moulded acrylic panels with an effect similar to Luxfer tiles; even Wadsworth’s failed century-old notion of internal deflecting glass is now proving practical with plastic panels and laser cutting, a technique promoted by the Australian firm Solartran. After decades hidden under paint and plywood, Pennycuick’s bright idea may get its day in the sun once again.
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