GE SHOWBIZ - Manual (Page 53)

GE LIGHTING - SHOWBIZ™ ENTERTAINMENT LIGHTING CATALOGUE 100
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.
GE LIGHTING - SHOWBIZ™ ENTERTAINMENT LIGHTING CATALOGUE 101
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.