Earthquake scales explained
While earthquake reports in the UK are frequently given using the Richter scale, it was actually replaced by the moment magnitude scale or MMS in the 1970s. Both Richter and MMS systems measure the energy released by an earthquake, however, this often has little influence over its effects.
In Japan (along with Taiwan) a different measurement system is used. The Japanese Seismic Intensity Scale measures the wobble of a quake at a specific point. Referred to in units of Shindo (literally translated as “degree of shaking”) it is not unusual for a quake to measure higher in one city than another.
It is this system which Sharp’s earthquake-sensitive streetlights use, triggering at a Shindo 5, at which point unreinforced concrete walls would be expected to fail, windowpanes could break and roads would likely suffer damage. It is also the level of shaking which triggers safety devices to cut off gas supply in equipped houses.
That’s the brainwave behind these earthquake-sensing street lamps, devised by Sharp. They feature seismic sensors in the unit’s aluminium support pole.
When a shake is detected above five on Japan’s Seismic Intensity Scale the unit switches on the full power of its 80 watt 1,800 lumen LED light.
The ultra-bright LED light stays switched on for two days, or until the battery runs out, drawing energy that’s been stored in a sealed lead battery within the street light, which charges during the day from its solar panel.
In normal circumstances, the LED street light stores enough power to run for a week without sunshine. In the case of an emergency, it pushes itself to the limit, operating at full brightness constantly for two days to help earthquake victims and rescuers alike.
Its independence from the national power grid means it’ll be unaffected if the power infrastructure is damaged too. Sharp estimates that installation of an LN-LW3A1 solar street lamp takes just one hour, since it doesn’t require an existing power infrastructure.
In the UK, London is in the process of switching to LED street lighting, and while there’s little danger of earthquakes here it’s heartening to know the technology is as smart as it is efficient.