Daniel K. Wright

Biography
Dan Wright was born on 25th September 1883 in Paterson, New Jersey. He joined the Engineering Department of the Edison Lamp Works at Harrison, New Jersey in the year 1909, and in 1922 he was put in charge of mechanical developments. Gradually the principal engineering and development operations within the GE lamp division became concentrated at Cleveland, Ohio, and in 1927 he relocated to the Lamp Development Laboratory at Nela Park¹.

Many lamp products are developed by teams of people, and several persons may be recognised as the principal developers or inventors. On the other hand there are products that have been marketed that are rightly associated with only a single person. The success of three lamp designs can be attributed mainly to one man, Daniel K. Wright. These are the incandescent lamps in which tungsten powder is present to allow bulb blackening to be eliminated by way of mechanical scrubbing, the high wattage incandescent lamps in the 10,000 to 50,000 watt range, and the sealed beam reflector lamp originally developed for use in automobile headlights.

He retired from NELA Park in the latter part of 1948⁷.

Development of Very High Wattage Lamps
Daniel Wright was the person behind two of the largest lamps ever produced. The practical incandescent lamp had its beginning with Thomas Edison in the year 1879, and as part of the 50th anniversary of this event Wright helped produce a 50,000 watt lamp. The bulb diameter was 20 inches, and it weighed 35 pounds. The lamp produced 1,600,000 lumens, as much as one thousand 100-watt regular lamps. The filament alone weighed 1.6 pounds, and contained enough tungsten to make 21,000,000 of the smallest 'grain-of wheat' lamps².

The principal challenge in this development was the development of the glass-to-metal seals, which can best be summarised from the reference below:

"To bring the 450-ampere leads inside the bulb, he modified the Housekeeper copper-to-glass seal which had been used in X-ray and other vacuum tubes...Through Wright's contribution and the development of iron-nickel-cobalt alloys in Germany and here, high-current and high-wattage lamps became practicable. Heavy leads were brazed to metal ferrules which, in turn, were sealed to the glass.This construction also withstood appreciably higher temperatures than previous designs and, with the development of Pyrex-type of glass bulbs, led to the design of compact bipost lamps of high wattage-to-size ratios."⁵

Then, in 1954, the 75th anniversary of the development of the Edison lamp took place. On that occasion a 75,000-watt lamp was produced, a picture of which is shown below⁴. The bulb diameter was 20 inches, its height is 42 inches and it weighed 50 pounds. The lamp produced 2,400,000 lumens, the equivalent of 2875 60-watt regular lamps. The filament weighed 2.7 pounds and was 12.5 feet long before coiling.

Development of Bi-Post Lamps
During Wright's development of the 50kW lamps, he changed not only the fundamental method of bringing the electric current into the bulb, but also the method of supporting the internal filament mount assembly. Prior to that invention the electric current was carried into practically all other lamps by metal wires, which either supported their filaments directly or with the aid of supplementary support wires fused into the glass stem assembly. It proved impossible to seal metal wires through the glass bulb capable of carrying the necessary 450-ampere current, due to excessive stresses created in the glass by mismatches in the thermal expansion coefficients of the glass and the wires. Wright therefore changed the design to use heavy copper tubes sealed to Pyrex glass, employing the so-called Housekeeper seal that had been used previously in similar high-current X-Ray and other vacuum devices. The great mechanical strength of that construction made it possible to support the filament entirely on the glass-to-metal seals without requirement for additional reinforcement via the glass stem components.

In the first high wattage lamps, the copper tubes were located inside the glass bulb. In a stroke of genius, Wright recognised the possibility to invert the design of the seals to place the copper tubes on the outside of the lamp - and thereby to eliminate the usual lamp base and to use the two copper posts themselves as the electrical and mechanical interface between the lamp and its holder. This fundamental change in design resulted in what became known as the 'Bi-Post Base' lamps, and introduced several other advantages which at once made this design attractive for lower wattage lamps that were being produced with the conventional wire-type glass-to-metal seals.

One of the principal requirements in lamps designed for optical projection and spotlighting applications is to have a very precise alignment between the incandescent filament, and the lamp base. This ensures that when one lamp is replaced by another, the filament will always be at precisely the same location and avoids the need for painstaking re-focussing of the filament at the necessary location. To overcome that limitation in conventionally sealed lamps, another GE engineer Robert S. Burnap invented the so-called Pre-focussed base in 1929. With that construction, after sealing the filament assembly into the bulb, the resulting dimensional variations arising from the glass sealing process were corrected by manually re-orienting the filament of every individual production lamp with respect to a special 2-part metal adjustable base. It was a labour-intensive but necessary operation to ensure optimum performance from image projectors and large spotlights.

With Wright's Bi-Post base, the filament can be mounted precisely with respect to the two copper posts that have been pre-sealed into a glass cup assembly, and that orientation does not change following sealing into the glass bulb. The result was a very considerable improvement in optical precision, along with a simplification in manufacturing. Moreover, it solved another problem associated with medium-wattage incandescent lamps in that the electrical connection quality was sometimes inadequate between the lamp bases and their holders, leading to overheating and burnout of the lampholders. The Bi-Post base construction presented a much larger and more robust electrical interface. As a result the new bi-post base construction was introduced in 1932 for the existing ranges of ten, five, two and one-kilowatt projection incandescent lamps. The Bi-Post construction remained the primary form of all incandescent lamps until the advent of tungsten-halogen technologies in the 1960s - and even those continued to make use of similar mechanical designs. Such lamps remained in production until 2007 when the last plant known to be still producing that type, the General Electric factory at Leicester in England, was closed down.

Immediately following the development of the Bi-Post base it was recognised that there were applications to extend its principles to even smaller projection lamps. However due to the mechanical properties of the copper posts used for the seals, it was difficult to seal them to glass when the diameter was reduced below a certain point. That limited the possibility to make lower wattage bi-post lamps in sufficiently small dimensions. The solution lay in a spinoff of Wright's original invention, by changing from copper to a new alloy whose expansion coefficient better matched that of the glass envelopes and which could be produced in smaller diameters. That resulted in the development of the so-called Medium Bi-Post and Miniature Bi-Post designs, and Wright's original copper-sealed lamps became known as the Mogul Bi-Post lamps.

Development of Sealed Beam Lamps
It can be seen from the above reviews that Dan Wright was a man having exceptional competence in the development of lamps having unusual mechanical and glass constructions, and not afraid to push the boundaries of lamp technology towards extremes that had previously been considered impossible. Following his development of the novel bi-post lamps, he soon recognised that the same principles could be applied to a novel form of high-precision reflector lamp.

With conventional projection lamps it had been made possible to precisely align their filaments with respect to the optical system either via Burnap's pre-focussed base construction, or via Wright's bi-post base construction. However, some kinds of lamps integrated the optical system within the bulb itself, for instance with the internal reflector bulbs that had been developed by GE's Royal F. Strickland in 1936. With that design the filament position vs the reflector was permanently fixed following the rather variable glassworking process of bulb sealing, and little could be done to correct that afterwards. That drawback limited the optical performance of all reflector type lamps, and there was considerable variation in beam distribution between individual lamps both within and between the production batches.

Around 1936, Wright recognised that his two-part lamp construction could overcome that limitation, and create a reflector lamp having immensely superior and more consistent performance. His concept was to enlarge the dimensions of the small glass cup used for the bases of his bi-post lamps, to shape the cup into the form of an optical reflector, and to coat it with an internal layer of vaporised aluminium as applied on his colleague's reflector bulbs. The filament could then be mounted to that assembly with very high precision, just as with the bi-post lamps. To complete the lamp, rather than sealing the reflectorised cup into a glass bulb or tube, it was closed by fusing a curved glass dish over to the reflector rim - thereby not disturbing the precise alignment of the filament with respect to either the reflector or the base assembly.

It must be remembered that at the time of Wright's idea, there were no facilities worldwide for producing even on an experimental scale a lamp such as he had conceived. He therefore set to work in 1937 using the materials available at the time, and started by purchasing a number of pressed glass custard cups from a local dime store. Those happened to be available with a convenient shape and dimensions to form the rear reflector part of the lamp. For the curved glass front lenses, he cut out dish-shaped sections from the spherical bulbs of his high wattage incandescent lamps, with a diameter to match the outer rim of the custard cups. Following a mastery of glassworking operations, Wright succeded to seal a pair of metal base posts into the custard cups, coat them with a vacuum-deposited aluminium reflector, mount the filaments, seal them to the glass lenses, and process them into finished and working reflector lamps.

The resulting construction must have looked completely alien to anyone involved in the lamp industry at the time - and thoroughly terrifying to consider how such a radically different construction could ever be optimised for production, and engineered into a low cost lamp for manufacturing by the millions. Had Wright not been fortunate to be employed by one of the world's most powerful enterprises with a rich array of experience in each of the necessary disciplines of metallurgy, glassworking, vacuum engineering and the capability to design and build its own manufacturing equipment, the idea would probably have been classified as far to expensive to possibly ever commercialise. However GE at the time was well used to such challenges, and recognised the potential market value of such a high-precision reflector lamp. Wright received the support he needed to take the idea into manufacturing, and just two years after his original patent, the first of the so-called 'Sealed Beam' lamps were marketed in 1939.

It grew to become one of the most important developments of the lamp industry, and numerous factories were built whose sole focus was the production of the necessary pressed glass components and assembly of these entirely different lamps. The development resulted in numerous other spinoffs for the electronic tube industry, and enormously facilitated the manufacture of many other electrical devices, such as the cathode ray tubes employed for television screens.

The pressed construction was considerably more expensive than the conventional blown reflector lamps, and it was clear from the outset that the new sealed beam lamps could not be promoted to ordinary general lighting customers. However one application that was in dire need of lamps having precise optical control, was that of the booming automotive industry. Early car headlights were not only dim and suffered imprecise beam shape, there were tremendous problems of variability of beam orientation which led to either not enough light on the road for drivers to see ahead, or too much light in the eyes of oncoming traffic. The blinding glare resulting from the latter risk set inconveniently low limits on the permitted intensity of automotive headlights. However, if the beam precision and alignment could be improved so as to reduce the glare for other road users, this would permit a corresponding increase in beam intensity could be justified - making the roads brighter and safer for all. That was precisely the application that GE selected for Dan Wright's invention of the sealed beam lamp, and which was used to justify the vast investments in building new processes, machines and factories to bring the new lamps into production.

So successful was the concept that within a year of its launch, in 1940 the United States ajusted the law to require that all new automobiles must use Wright's sealed beam lamps - a situation which did not change until as recently as 1984. The original design consisted of a 7-inch PAR-56 lamp containing two filaments so as to provide both the dipped (low) and driving (high) beams. In 1957 the use of a four-lamp system was legalised, and the smaller 5¾ PAR-46 lamps were introduced. One contained two filaments for both dipped and driving beams, and the other contained only one filament so as to provide a brighter high beam. From the 1975 model year, the novel rectangular sealed beam lamps were introduced for the four-lamp system, which had a profound effect on the styling of cars of that era. The first rectangular lamps measured 6½ x 4 inches, and in 1978 an 8 x ½ rectangular lamp was introduced for the two-lamp headlighting systems. Even following the advent of tungsten-halogen lamps for American automotive headlamps from 1979, the US Government still considered that the advantages for safety of the sealed beam invention were so significant that the halogen capsules must be provided within the sealed beam reflector units. In other countries of the world the regulations were less severe, and although the sealed beam lamps were not completely mandated they still made up for a major portion of the sales.

As such, there is perhaps no one man other than Daniel Wright, whose inventions had such a profound impact on the lighting and resultant styling of automobiles over such a long period of time.

Thanks to the tremendous volumes of sealed beam lamps required for the automotive industry, the production costs fell quickly as improved methods for their high efficiency production were devised. It had originally been believed that they would be far too expensive to compete in general lighting, but already during the 1940s the compact PAR-38 sealed beam lamp was introduced for commercial spot and floodlighting. Although it always remained more expensive than the blown reflector alternatives, the considerable improvement in optical performance made it the favoured reflector lamp for more professional lighting applications. Its position remained unchallenged for four decades until the 1980s dominance of low voltage halogen spotlights, but the PAR38 evolved and was also upgraded to contain halogen, discharge and even LED light sources instead of the filament, and even today remains one of the most important formats of reflector lamps.

Sealed Beam technology dominated countless other markets beyond the automotive and general lighting industries, perhaps one of the most important being the entertainment lighting business. Very soon after its invention, theatrical and studio lighting engineers recognised the potential of these high-precision light sources, leading to the development of the highly simple but also extremely robust 'PAR Can' lanterns. For many decades these were the workhorses behind practically every entertainment lighting venue around the world, and despite recent challenges by superior discharge and LED sources, their low cost and simplicity ensures that they still maintain a dominant positrion.