Electric heater

An electric heater for arranging beneath a translucent cooking plate includes at least one electrical heating means, such as a ribbon, coil or filament lamp, in a housing comprising a base and a peripheral wall. Light indicator means is supported peripherally on the heater and visible, in operation, through the cooking plate. The light indicator means comprises an elongate light-emitting device at least partially surrounding the heater and arranged to emit light towards the underside of the cooking plate. Mask means is provided overlying the device and integral with the heater, the mask means being of a material substantially opaque to light from the device. The mask means has one or more apertures, different in configuration to the configuration of the device, through which one or more apertures light from the device is visible, viewed through the cooking plate.

This invention relates to an electric heater, such as a radiant electric 
heater, for arranging beneath a translucent cooking plate, such as a 
glass-ceramic cooking plate. More particularly, the invention relates to 
such a heater having at least one electrical heating means, such as a 
coiled wire, elongate electrically conductive ribbon, or tungsten-halogen 
lamp, in a housing comprising a base and a peripheral wall. 
BACKGROUND TO THE INVENTION 
It is known to provide light indicator means supported peripherally on a 
heater and visible in operation through the cooking plate, the indicator 
comprising an elongate light-emitting device at least partially 
surrounding the heater and arranged to emit light towards the underside of 
the cooking plate. In the case of a circular heater, the elongate 
light-emitting device is arranged to be correspondingly circular, or 
part-circular. 
Such light indicator means serves particularly as a hot warning indicator 
for providing a visual warning when the translucent cooking plate is at a 
temperature at which it is unsafe to be touched. 
DESCRIPTION OF PRIOR ART 
Electric heaters having light indicating means of this type are described, 
for example, in EP-A-0 359 028, EP-A-0 438 656, and GB-A-2 271 840. The 
light indicating means may, for example, comprise an elongate filament 
lamp or an elongate gas discharge lamp, such as an elongate neon lamp. Of 
particular interest, however, is an indicating means comprising an 
elongate light guide, such as an appropriately-shaped glass rod, having a 
light exit region facing the underside of the cooking plate, and 
preferably extending substantially along the length of the light guide, 
and having at least one light entry region, such as one or both ends of 
the glass rod, arranged to receive light from a light source. The light 
from the source is transmitted along the light guide and the source 
suitably comprises a filament lamp, such as a tungsten-halogen lamp. 
In operation, the light indicating means, viewed through the cooking plate, 
is observed as a ring of light surrounding the heater. Such a ring may be 
continuous or may take the form of a series of bright spots, the latter 
being achieved by means such as providing a series of spaced-apart notches 
in the surface of the light guide. 
In practice, however, the observed ring of light, whether continuous or in 
the form of bright spots, may not be sharply defined or of uniform 
brightness and stray light may be visible through the cooking plate. This 
is aesthetically undesirable. 
Furthermore, there is a requirement to be able to provide sharply-defined 
patterns of illumination which can readily be varied from one heater to 
another, if required, to meet specific visual requirements in different 
cooking appliances, without requiring modification to a basic elongate 
light-emitting device. Such specific visual requirements may also include 
patterns of illumination incorporating designs or logos. 
OBJECT OF THE INVENTION 
It is an object of the present invention to fulfill these requirements and 
overcome or minimise the disadvantages of the prior art. 
SUMMARY OF THE INVENTION 
The present invention provides an electric heater for arranging beneath a 
translucent cooking plate, the heater comprising: at least one electrical 
heating means in a housing comprising a base and a peripheral wall; light 
indicator means supported peripherally on the heater and visible, in 
operation, through the cooking plate, the light indicator means comprising 
an elongate light-emitting device at least partially surrounding the 
heater and arranged to emit light towards the underside of the cooking 
plate, wherein mask means is provided overlying the device and integral 
with the heater, the mask means being of a material substantially opaque 
to light from the device and having one or more apertures therein, 
different in configuration to the configuration of the device, through 
which one or more apertures light from the device is visible, viewed 
through the cooking plate. 
The apertures are selected with regard to number, size, shape and position 
to provide any particular desired visual effect with good uniformity of 
brightness. 
In a particular embodiment, a plurality of apertures are provided in the 
mask means, in spaced-apart relationship along the length of the 
light-emitting device. 
The mask means is formed of a material capable of withstanding the 
operating temperature environment of the heater. It suitably comprises an 
appropriately opaque material selected from the group consisting of 
metals; ceramics; ceramic fibre materials; glass cloth materials. 
The mask means may suitably be formed from material in sheet or strip form 
and may optionally be provided of substantially L-shaped cross-section 
whereby a downwardly-directed flange portion, preferably unapertured, 
provides screening of light radiating laterally from the light-emitting 
device and/or provides a means for securing the mask means to the heater. 
The base and peripheral wall of the heater may comprise thermal and 
electrical insulation material suitably located in a supporting dish, such 
as of metal. 
The light-emitting device may be located in a recess or rebate provided in 
the upper surface of the peripheral wall. The mask means may overlie the 
surface of the peripheral wall, at least in part, or may be flush with, or 
lower than, the surface of the peripheral wall. 
Preferably the light-emitting device substantially surrounds the heater. 
The mask means may serve to secure in location the light-emitting device. 
The light-emitting device may be provided of various forms. It may comprise 
an elongate filament lamp or an elongate gas-discharge lamp such as a neon 
lamp. It may advantageously comprise an elongate light guide having a 
light exit region facing the underside of the cooking plate, and 
preferably extending substantially along the length of the light guide, 
and having at least one light entry region arranged to receive light from 
a light source, the light from the source being transmitted along the 
light guide. 
The light entry region(s) may comprise one or both ends of the light guide. 
The light source suitably comprises a filament lamp, such as a 
tungsten-halogen lamp. 
The filament lamp may be located inside a housing, suitably of metal or 
ceramic material, which is provided with one or more apertures therein to 
receive the one or both ends of the light guide. The housing may have an 
interior surface which is light-reflective such as by provision thereon of 
a metallic, or other suitable, layer. 
The light guide suitably comprises a glass rod which may have a 
substantially circular cross-section, although other cross-sections such 
as rectangular, oval, or triangular, could be considered. 
The surface of the glass rod is adapted to allow egress of light from the 
light exit region facing the underside of the cooking plate. In this 
regard, at least an elongate surface strip of the rod constituting, and/or 
diametrically opposite, the light exit region may be frosted or etched or 
micro-roughened. Such frosted or etched or micro-roughened surface strip 
may be graded in degree such that the degree of frosting, etching or 
micro-roughening increases with increasing distance along the rod from the 
light entry region or regions, for example as described in GB-A-2 271 840. 
By this means, facility of egress of light from the light exit region 
increases with increasing distance along the rod from the light entry 
region or regions and light emitted towards the underside of the cooking 
plate is of substantially uniform intensity along the rod. 
As an alternative to a frosted or etched or micro-roughened elongate 
surface strip, a corresponding elongate surface strip of the rod opposite 
the light exit region may be coated with a light-reflective paint, enamel 
or lacquer, preferably of a light colour such as white. The coated strip 
may be tapered in width, such that the width increases with increasing 
distance from the light entry region or regions, whereby substantially 
uniform density of emitted light along the rod is obtained. 
In a particular embodiment, the electric heater is of substantially 
circular shape and the elongate light-emitting device is of corresponding 
circular, or particular, shape. 
The light indicator means comprising the elongate light-emitting device is 
particularly suitable for use as a hot warning indicator for providing a 
visual warning when the translucent cooking plate, which is usually of a 
glass-ceramic material, is at a temperature at which it is unsafe to be 
touched. 
The invention is now described by way of example, with reference to the 
accompanying drawings in which:

DESCRIPTION OF PREFERRED EMBODIMENTS 
A radiant electric heater, for use in a cooking appliance having a 
translucent glass-ceramic cook top, is constructed as follows. A circular 
metal dish 1 contains a base layer 2 of thermal and electrical insulation 
material, such as microporous thermal and electrical insulation material, 
which is well known to the skilled person. A heating element 4, in the 
form of a corrugated metal alloy strip 5, whose corrugations are not shown 
for simplicity, is secured to the base layer 2 by embedding therein to 
part of its height. If desired, the strip 5 of the element 4 may be 
profiled along that edge thereof which is embedded, for example by 
providing downwardly-extending integral spaced-apart tabs (not shown) 
which are embedded in the insulation material of the base layer 2. 
Instead of, or additional to, the strip-form heating element 4, other 
well-known forms of heating element may be provided, for example a coiled 
wire heating element and/or a bright radiating element such as a 
quartz-halogen lamp or a molybdenum disilicide element. 
A terminal connector 6 is provided for electrically connecting the heating 
element 4 to an electrical supply for operation thereof. 
Against the side of the dish 1 is located a peripheral wall 3 of thermal 
insulation material whose top surface 8 is arranged in use to contact 
directly, or indirectly, the underside of a translucent glass-ceramic 
cooking plate 9 in a cooking appliance. 
A well-known form of thermal cut-out device 7 is provided, extending over 
the heating element 4. The cut-out device 7 has two sets of switch 
contacts. One set of contacts is connected to, and arranged to switch off, 
the heating element 4 to prevent over-heating when the heater is installed 
and operating in a cooking appliance. 
The other set of switch contacts in the cut-out device 7 is arranged for 
connection to a light indicator means, described hereinafter, which is 
visible in operation through the translucent glass-ceramic cooking plate 9 
and serves to provide a visual warning that the surface of the cooking 
plate is too hot to touch and/or to provide a visual delimitation of that 
area of the cooking plate beneath which the heater is positioned. The 
light indicator means may be arranged to be illuminated, for example, when 
the temperature of the cooking plate reaches about 40.degree. C. 
The light indicator means comprises an elongate light guide in the form of 
a circular light-transmitting glass rod 10 which is located in a rebate in 
the peripheral wall 3 of the heater and substantially surrounds the 
heater. The light-transmitting rod 10 has ends 11, 12 which locate in 
apertures in a housing 13 which encloses a light source in the form of a 
halogen lamp 14. The housing 13 is suitably of ceramic or metal material 
and preferably has a light-reflective inner surface to enhance 
illumination of the ends of the light transmitting rod 10. the 
light-reflective inner surface may suitably comprise a metallic layer on 
the housing. The lamp 14 is connected to a suitable electrical supply 
through one of the sets of switch contacts in the cut-out device 7 and 
becomes illuminated when the cooking plate 9 reaches a predetermined 
temperature, such as 40.degree. C. 
Light from the lamp 14 is transmitted along the rod 10 and is arranged to 
exit radially from the rod, towards the glass-ceramic cooking plate 9. 
This is achieved by providing an etched, frosted or micro-roughened 
surface strip 15 along the length of the rod on that region of the rod 
either adjacent to, or diametrically opposite, the cooking plate 9, as 
described for example in GB-A-2 271 840. The etched, frosted or 
micro-roughened surface strip 15 is preferably graded such that there is 
an increasing degree of etching, frosting or micro-roughening with 
increasing distance from the ends 11, 12 of the rod where the lamp 14 is 
provided. By this means, substantially uniform brightness of light exiting 
from the rod 10 towards the cook top 9 is achieved along the length of the 
rod 10. 
A mask means 16 is provided overlying the light transmitting rod 10 and 
integral with the heater. The mask means in its simplest form comprises a 
ring-shaped thin strip 17 of substantially light-opaque material provided 
with a pattern of apertures 18 therein different in configuration to the 
configuration of the light transmitting rod 10. The thin strip 17 suitably 
comprises a metal, although other substantially light-opaque materials 
such as ceramics, ceramic fibre materials or glass cloth materials could 
be considered. Preferably, a downwardly-directed flange portion 19 is 
provided on the ring-shaped strip 17 so that the resulting mask means is 
of substantially L-shaped cross-section. As shown in FIG. 2, the mask 
means locates the light transmitting rod 10 in position, the flange 
portion 19 being suitably secured to the metal dish 1 of the heater by 
forming an interference fit therewith or by means 20, such as threaded 
fasteners or spot welds. The upper surface of the strip 17, which is 
provided with the apertures 18 is arranged to be level with, or slightly 
below, the top surface 8 of the peripheral wall 3 of the heater, but may 
be arranged to overlie, at least in part, the top surface 8 of the wall. 
In operation, light exiting radially from the light transmitting rod 10 
passes through the apertures 18 in the mask means 16 and is visible as a 
sharply defined substantially uniformly bright circular pattern through 
the cooking plate 9. The mask means 16, particularly with its flange 
portion 19, prevents stray light from the rod 10 escaping in undesirable 
directions, particularly laterally. 
It may be advantageous for the interior of the mask facing the 
light-transmitting rod 10 to be light-reflective, at least in part. 
Any desired number, shape and pattern of apertures may be selected to 
provide a particular required visual effect. One or more apertures may be 
shaped in conformance with a logo identifying, for example, the 
manufacturer or supplier of the heater or cooking appliance. 
By a straightforward change of apertured mask, different visual patterns 
may be provided from one cooking appliance to another. 
Instead of the light transmitting rod 10 and lamp source 14, a ring-shaped 
discharge lamp, such as a neon lamp, could be used, or a ring-shaped 
filament lamp, the mask means 16 being equally suitable for use with these 
alternative arrangements. In this respect, FIG. 3 illustrates a 
ring-shaped filament lamp 10a in conjunction with a mask that is 
substantially flush with the upper surface of the peripheral wall 3 and 
FIG. 4 illustrates a ring-shaped discharge lamp 10b in conjunction with a 
mask that is at a level lower than the upper surface of the peripheral 
wall 3.