Red steady-burning rear lights, brighter than the rear position lamps, are activated when the driver applies the vehicle's brakes. These are formally called stop lamps in technical standards and regulations . and in the Vienna Convention on Road Traffic, though informally they are sometimes called "brake lights". They are required to be fitted in multiples of two, symmetrically at the left and right edges of the rear of every vehicle. International UN regulations specify a range of acceptable intensity for a stop lamp of 60 to 185 candela. In North America where the UN regulations are not recognised, the acceptable range for a single-compartment stop lamp is 80 to 300 candela.