Installed in Canada from about 1934, mercury bulbs became very popular after the Second World War because of increased automobile traffic and the construction of highways. They are preferable to incandescent bulbs because they have a long life, provide considerable light and cost less to maintain.

With a life span of 1000 hours, these 250-watt bulbs (fig. 21) have a tubular burner in quartz containing pure argon and mercury to conduct the electric current.

Fig. 21 Mercury vapour bulb, manufactured by Canadian General Electric Co., ca 1939–1947. (921694)

Over time, improvements were made to the watertight enclosure and the design of the electrodes; the egg shape was adopted about 1950. After 1958, these bulbs (fig. 22) were given a phosphorescent coating to increase their light output while retaining a pleasant look. With a power level of 175 watts and a life span of 16 000 hours, this bulb is well suited for lighting commercial, industrial and recreational spaces.

Fig. 22 Mercury vapour bulb, manufactured by Sylvania Canada, ca 1966. (921697)

Designed to dispense high-intensity lighting along major arteries and highways, the "cobra-head" light standard (fig. 23) was an innovation of the 1960s. It was equipped with a transformer or ballast to regularize the voltage and current. It continues to light up Canada's highways today.

Fig. 23 Light standard for major roads, manufactured by Powerlite Devices Limited, Toronto, ca 1965. (921679)