Electric discharge lamps

H. G. MOLYNEUX

ELECTRIC DISCHARGE LAMPS

Oct. 29, 1957

Filed June 22, 1956

2,811,671

Sheets-Sheet 1

<img file="US2811671A_D0001.tif" />

H. G. MOLYNEUX

ELECTRIC DISCHARGE LAMPS

Oct 29, 1957

Filed June 22, 1956

2,811,671

Sheets-Sheet 2

<img file="US2811671A_D0002.tif" />

United States Patent Office

2,811,671

Patented Oct. 29, 1957

2,811,671

ELECTRIC DISCHARGE LAMPS

Harold Grosvenor Molyneux, Ribbleton, Preston, England, assignor to Siemens Edison Swan Limited, a corporation of Great Britain

Application June 22, 1956, Serial No. 593,208

Claims priority, application Great Britain July 1,1955

Claim. (Cl. 315—49)

The present invention relates to mercury vapour electric discharge lamps and more especially to lamps emitting ultra-violet rays for medical treatment and which are suitable for domestic use. Such lamps may be used domestically for producing a tanning effect of the human skin.

It is well known that mercury vapour electric discharge lamps emit erythemal radiation which in the shorter wave lengths (e. g. the emission at a wave length of 2537 Angstrom units) may be harmful unless special precautions are taken and this radiation is present not only during the normal operation of the lamp but also during the running up period. In the lamp of the present invention the amount of harmful radiation is reduced both in the normal operation of the lamp and during its running up period without reducing to an appreciable extent the beneficial longer wave ultra-violet radiation (e. g. the emission at a wave length of 3650 Angstrom units).

According to the present invention, there is provided a mercury vapour electric discharge lamp in which the discharge tube proper is shielded to a partial but significant degree, so far as external objects irradiated by the lamp are concerned, by a shielding member composed of material that is transparent to radiation of wave lengths in a wide range extending from about 3000 Angstrom units upwards and including 3650 Angstrom units, but is substantially opaque to radiation of wave lengths in a wide range below 3000 Angstrom units and including 2537 Angstrom units. The shielding member serves to filter out a portion of the lower wave length erythemal radiation emitted by the discharge tube. A suitable material for this shielding member is the glass known under the trade name “Pyrex.”

The shielding member is in the form of a helix surrounding, but spaced from, the discharge tube proper. With a shielding member of this form, the proportion of the total lower wave length erythemal radiation from the discharge tube which is rendered ineffective can readily be made to have a desired value by suitable choice of the dimensions of the member which is coiled to form the helix and of the diameter and pitch of the helix. The dimensions of the helix may suitably be such that approximately one half the surface of the discharge tube proper is obscured when the lamp is viewed from the front.

The shielding member is in the form of a helix which surrounds the discharge tube proper and which is constituted by a coiled tube, and this coiled tube has running through it a length of resistance wire constituting a ballast resistance for the discharge tube, and the helix, although spaced from the discharge tube, surrounds the discharge tube sufficiently closely for the heat generated in said ballast resistance to shorten materially the time taken for the discharge tube to run up to the full discharge condition when the lamp is switched on. The specific material previously mentioned as being suitable for the shielding member is especially suitable, since it is such as to withstand the heat dissipated by the discharge tube proper and the ballast resistance.

® By way of example, a specific embodiment of the invention will now be described with reference to the accompanying drawings. The embodiment concerned takes the form of a mercury vapour electric discharge lamp for medical treatment, the lamp being one provided with a shielding member constituted by a coiled tube, and this coiled tube containing a ballast resistance for the discharge tube proper. Fig. 1 of the drawings shows a front elevation of the lamp, Fig. 2 shows a side elevation, and Fig. 3 shows a plan. The lamp has a base ¹⁵ member 1 of insulating material which is provided at its four corners with bolts 2 and nuts 3. The bolts 2 and nuts 3 enable the lamp to be suitably mounted for use. Supported above the base 1, by suitable supporting and electrical conducting members 4 and 5 securely fixed in ²⁰ this base, and various auxiliary supporting members, are the mercury vapour discharge tube proper 6 and the shielding member 7. The shielding member 7 is formed of a tube of the glass known under the trade name “Pyrex,” and contains a ballast resistance 8 which is ²⁸ connected in series with the discharge tube 6 and consists of a coiled length of resistance wire of the kind known as Nichrome. Two terminal arrangements 9 and 10 are connected to the members 4 and 5 respectively 30 ^menlbers 11 and 12 respectively. A reflector 13 is supported by two members 14 and 15 securely fixed in the base 1. The shielding member 7, although spaced from the discharge tube 6, surrounds the latter sufficiently closely for the heat generated in the ballast resistance 8 ₃₅ to shorten materially the time taken for the discharge tube to run up to the full discharge condition when the lamp is switched on. The discharge tube 6 takes the form of a conventional 125-watt tube about 5 cms. in length, and the shielding member 7 in which the ballast resistance is contained is a tube of approximately 5 millimetres bore wound in the form of a helix having a diameter of 2 cms. with the turns spaced 1 cm. apart. With a suitable ballast resistance such a lamp may be operated directly from 200-250 volt mains.