Gone are the days when an electricity company employee needed to light pole by pole: today, this job is done automatically, respecting the decrease in natural light. The poles are equipped with sensors known as photocells or photoelectric relays, which detect the moment when sunlight is no longer sufficient to illuminate the site. Such photocells are cup-sized boxes with openings for light rays to enter. When the sun goes down and the incidence of light decreases, they send a signal to the city’s energy distributor and that’s it: the light from the lamps is turned on. At dawn, the opposite occurs: the photocell detects the first rays of light and notifies the system that the lights can now be turned off. At this point, you must be wondering: and on cloudy days, do we run the risk of running out of light? None of that, because even if the Sun does not appear, its rays are detected. The difference is that, with less sun, the lights are turned on earlier: in winter, around 6 pm, an hour and a half earlier than in summer. In a city like São Paulo, where the distance between posts is usually no greater than 40 meters, a sensor triggers an average of 40 light bulbs. In rural areas, where the distance between the posts is greater, the photocell turns on fewer lamps. But this clever scheme does not completely dispense with human labor. Every night, city officials make the rounds to see if any photocells have malfunctioned and left areas of the city in darkness.
gas lamps
Until the mid-19th century, most Brazilian cities lived in the dark. That’s when the first gas lamps appeared, lit manually, one at a time. In São Paulo, they appeared in 1872, but only in the center. The periphery continued in the dark
incandescent light bulbs
The lamps soon disappeared: from 1883 onwards, electricity and incandescent light bulbs (the same ones we use at home) arrived on Brazilian streets. But lighting was still manual, using keys that connected 20 to 40 poles.
Mercury and sodium lamps
In 1966, another innovation: mercury vapor lamps, with a stronger and whiter light, replaced the incandescent ones, which were yellowish. From 1989, sodium lamps appear. Used to this day, they are four times more efficient