Projector lamps are frequently made with an internal reflector to direct a greater portion of the created light towards the film being projected. An early reflector form was made from a glass substrate with a metal coating, such as aluminum or silver on the glass. Glass substrates break, and the metal coatings can be scratched during assembly. A current design uses a copper reflector base with a nickel coating. A final surface coating of silver is apPlied to the nickel. Plated cop per reflectors are costly to make both because of the expensive materials, and because of the additional labor needed in the multiple processing steps.
Unfortunately, plated copper reflectors experience a manufacturing problem known as "blooming", where a white, cloudy area or spot appears on the reflector surface. A cloudy reflector makes the product photometrically and cosmetically unacceptable. "Blooming" is not a rare occurrence, and has at times occurred to some degree in approximately twenty percent of the lamps produced. There is then a need for an internal reflector that is inexpensive to make and does not cloud or spot prior to, or during operation.
Silver plated copper reflectors are relatively heavy with respect to the rest of a lamp. The reflector can develop a large moment during lamp motions that may result in a large deceleration force when the lamp is stopped. The heavy reflector then stresses the reflector supports, and seal, causing assembly or transport failure of the lamps. There is then a need for a reflector lamp with a light weight reflector.
Aluminum reflectors are light weight and inexpensive to make, but under normal circumstances pure aluminum is known to oxidize quickly which may result in tarnished surfaces with a lowered reflectivity. It is therefore common in the industry to form an enhanced oxide skin on the surface of aluminum products. The oxide skin, commonly produced by anodizing the aluminum, protects the aluminum from further oxidization and other chemical corrosion. By some accounts, anodizing aluminum is so common that it may be considered a standard, and perhaps even a required procedure. It is also known that anodized aluminum may be polished to produce a surface that is highly reflective, and resistant to tarnishing. Unfortunately, anodized reflectors have been tested in lamps and found to cause severe envelope wall blackening. There is then a need to formulate an aluminum reflector that does not cause wall blackening.
Lamps in general and projector lamps in particular are known to fail due to oxygen attacking the filament and accelerating tungsten evaporation. Oxygen may be mistakenly included in filling procedures, or may cling to the inner surfaces of the various lamp components. Getters are used in lamps to collect oxygen or other detrimental components in the lamp fill. There is then a need to improve the life of a reflector lamp by limiting oxygen attack of the filament.
Tungsten slowly evaporates at the white hot operation temperatures typical of incandescent lamp filaments. Evaporation leaves the filament progressively weaker, while the evaporated material deposits on the envelope walls, reflector, and other enclosed elements. The settled material clouds the optical surfaces and reduces the projected light. For reading and area lighting this may be a tolerable result, but for slide and film projection, a higher standard is felt to apply. There is then a need to reduce lamp clouding, particularly in projector lamps.