mailing list
site map


Radiovisor Parent Ltd.
28 Little Russell Street
London, WC1
Radiovisor Parent Ltd.
Darnoc House
36 Alfred Place London, WC1

Provided light-sensitive control for all types of lighting including both AC and DC lighting units of various capacities. Designs were available for both wall type and spigot cap mountings. The units found a niche application in "Danger" and "Keep Left" etc. signs so they require a minimum of attention. An interesting modified (or inverted) use was suggested where units could be placed in shops and actuated by the torch of policeman if he wanted to inspect the shop; modifications to signs which would switch on when illuminated by the passage of a vehicle or person were also suggested. - APLE Exhibition Catalogue 1932

In these days of fast-moving traffic, Light Actuated Apparatus is being particular used for the control of illumination of such important points as Traffic Circuses, Traffic Islands, including "Danger" and "Keep Left" signs. An improved Radiovisor Lighting Unit (Series 70) has been introduced which uses an entirely new principle of operation and is applicable to both A.C. and D.C. supplies. - Public Lighting #1, 1936

A selenium cell (known as the Radiovisor Bridge) is connected in series with a fixed resistance which at the point of operation is of equal value to the resistance of the bridge, across the mains voltage thus dividing it between (1) the bridge or variable light sensitive resistance and (2) the fixed resistance. In daylight the minute current allowed to pass by the bridge is stored up as a charge on a condenser, across which is a gaeous discharge tube having in series with it the coil of a polarised relay. As darkness approaches the bridge resistance rises, the potential across it and the condenser also rises until the striking voltage of the discharge tube is reached where it flashes and the current passed flows through the coil and so operates the relay. Thus the lighting is then switched on. A second combination of contacts on the relay transfers the condenser circuit across the fixed resistance (2) ready for the next operation in the morning when, due to the falling resistance of the bridge, the potential across the fixed resistance reaches, in its turn, the striking voltage of the same tube and the relay is again operated and switches off. - Public Lighting #2, 1936

Typical island refuge lighting scheme in Chiswick.
The Radiovisor unit controls both the centre lamp and the guardposts.
Bridge housing mounted on top of the harp bracket and controller mounted
mid-way up the post. Public Lighting #3, 1936

The Series 70 control is on display at the 1936 APLE Conference in Cheltenham. It contains no valve or other expendable part, gives a decisive switch action, is adaptable for both AC and DC supplies and has been specially designed to stand up to all conditions of service. - Public Lighting #3, 1936

A special exhibit was shown at the I.M.E.A. Exibition in Torquay of the Radiovisor Lighting Unit for the control of the illumination of traffic islands and bollards. This unit is designed to brign on, or leave on, the lighting should any component become damaged. The Radiovisor Smoke Indicator And Recorder for boiler plants and the Radiovisor Smoke Alarm were also exhibited. - Public Lighting #10, 1938

Again exhibited their Light-Actuated Controls for Street Lighting including a special exhibit for the illumination of traffic silands and bollards. This unit will bring on, or leave on, the lighting should any component of the unit circuit become damaged or defective. It is also noted that being a "Dusk To Dawn" device then it fulfils the "control" recommendation in the MOT's Final Report on Street Lighting. - APLE Conference Programme 1938

Sectional diagram showing how the selenium cell was incorporated
within specially designed finial in bracket designed for Eastbourne.
1938 Paper

The firm have issued an illustrated brochure by Col. the Hon. Arthur Murray, C.M.G, D.S.O. It contains descriptions of various kinds of Radiovisor Light-Ray apparatus. The automatic control of street lighting is called Sky Control. Being a "dusk to dawn" switch, it fulfils the "control" recommendations of the MOT's Final Report on Street Lighting. The apparatus is functioning over 150 miles of streets in the Metropolitan area and also used in South Africa, Australia, New Zealand and Palestine - Public Lighting #11, 1938

Moved to larger premises at Darnoc House in April 1939. - Public Lighting #13, 1939

The firm point out that their units are being increasingly used in areas where street lamps are lighted from dusk to dawn. The light-actuated switch has also been used for Traffic Circuses, Traffic Islands, Bollards and Danager Signs. - APLE Conference Programme 1939

One of their principle units is the Automatic Street Lighting Control Unit. It is essentially a "Dusk To Dawn" control and meets the recommendatins contained in the MOT's Departmental Committee Report on Street Lighting. The lighting remains on if the unit become defective. This unit has been in successful operation for some fifteen years (so introduced in 1930). - APLE Conference Programme 1945

Of special interest is the Radiovisor Mark X Lighting Control unit. There is an obligation on local authorities to keep illuminated all Traffic Islands, Bollards, Guard Posts and "Danger" Signs, not only at night-time, but also during the daytime, should premature darkness occur causing these to become a danager. The use of the Radiovisor Lighting Control Unit is ideal for this purpose. It has been found to be thoroughly reliable in service with a very low maintenance cost. - APLE Conference Programme 1946

APLE Exhibition Catalogue Blackpool 1932
APLE Conference Programme Bournemouth 1938
APLE Conference Programme Glasgow 1939
APLE Conference Programme Glasgow 1945
APLE Conference Programme London 1946
APLE Conference Programme Southport 1947

External Links:
Grace's Guide