Hard glass Halogen compared with Quartz Halogen
The tungsten halogen principle is now so well known and documented elsewhere that it is considered unnecessary to describe it here. However should you require details of this principle then please contact GE Lighting Ltd or your nearest Subsidiary Company. It is important to distinguish between hard glass lamps that merely have a halogen compound added to the filling gas and lamps such as those enumerated, which are of quartz construction. The former are from the point of view of life and performance identical to conventional glass lamps of the same rating, the halogen only serving to prolong the usefulness of the lamp by preventing internal blackening due to evaporated tungsten. However, once a lamp is constructed from quartz with its higher melting point, instead of glass, the designer can make use of the much greater strength of the small envelope. It is then possible to increase the filling pressure which by reducing tungsten evaporation from the filament prolongs the life of the lamp to at least twice that of a glass lamp of equivalent efficacy.
Biplane or Monoplane?
The filament format of a lamp will have an effect on the beam performance of a luminaire.
In Fresnel optics a biplane filament will, due to its smaller area, produce a narrower spot of slightly increased peak intensity, compared to an equivalent monoplane filament. However, in intermediate and flood positions better light collection is obtained from a monoplane source, as the additional light collected by the rear mirror is largely obscured with a biplane source. A wider angle beam for a given intensity is thus provided by a monoplane filament.
Ellipsoidal optics are designed around a specific filament area. Larger areas will allow some of the light to fall outside the gate and be lost. A smaller filament area will concentrate the light on the centre of the gate producing a hot spot. The choice between a monoplane and a smaller equivalent biplane is, therefore, dependent on luminaire design and customer preference.
GE pursue a policy of allowing the customers to make this choice by offering both monoplane and biplane versions of relevant lamp types.
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