A street light decides nothing. A sensor tells it night has fallen, a cabinet on the corner sends it power, and someone at the town hall chose the hour it switches off.
How a street lights up
The control cabinet. Street lights aren't wired to the grid one by one. They form circuits of a few dozen lights, fed by a grey metal cabinet, often at the foot of a wall or next to a transformer. It holds the protection, the meter and the switching.
Switching turns the whole circuit on and off at once:
- either by a photocell, a small light sensor on the cabinet or on a lamp post, which switches on when daylight drops below a threshold;
- or by an astronomical clock, which works out sunset and sunrise for the town every day;
- more and more, by remote management: each light gets its orders remotely and can dim in the middle of the night.
Night switch-off. Thousands of French towns turn off part of their lighting in the dead of night, often between midnight and 5 am, to save energy and limit light pollution. The law also governs the direction and colour of the light.
The pole
A lamp post stands 4 to 12 metres (13 to 40 ft) tall depending on the road: low in pedestrian streets, tall on highways. The column is a hollow tube of galvanised steel or aluminium. At the base, a small hatch gives access to the connection box and the fuse for that light.
Lamps, from oldest to newest
| Lamp | Light | What to know |
|---|---|---|
| Gas | Soft yellow | City lighting in the 19th century. A lamplighter came by every evening with his pole. |
| Mercury vapour | Bluish white | Banned from sale in the European Union since 2015, still in place in forgotten corners. |
| Low-pressure sodium | Pure orange | Very efficient, but a single colour: under it, you can't tell red from green. |
| High-pressure sodium | Golden orange | The light of roads and cities for forty years. Takes several minutes to reach full brightness. |
| Metal halide | White | Squares, stadiums, monuments. |
| LED | White, warmer or cooler | The standard today. Half the energy of sodium, instant on, dimmable. |
The solar street light
In car parks, on cycle paths and at isolated stops, more and more street lights are self-contained: a solar panel at the top of the pole, a battery (often lithium iron phosphate) in the pole or under the panel, a charge controller, an LED head and a motion sensor. No cable connects them to the grid. See Le solaire photovoltaïque, du panneau à la prise.
What the maintenance crews know
- Orange light hides colours. Under sodium lighting, a map, colour-coded wiring or a wound is hard to read. A white head torch changes everything.
- During a general blackout, solar street lights stay on. They're often the only light in a neighbourhood. And each is a complete, self-contained kit: panel, battery, controller, LED light, which once taken down can light a room or charge a small battery. See Powering a circuit without the grid.
- The hatch at the base of the pole is live. The supply cable is connected there at 230 volts, sometimes more. A hatch torn off after a crash gets reported, not explored.
- Cover a photocell and it thinks it's night: that's how technicians test lights in broad daylight. A photocell covered in bird droppings or badly aimed explains a street lit at noon.
- A street light that blinks at the end of its life is almost always a sodium lamp that switches off as it heats up and comes back on as it cools.
- Lighting attracts insects, especially under white and blue light. That's one reason for moving to warmer, orange-tinted LEDs near natural areas.