Light-emitting device and measurement device

A light-emitting device comprising:

• a substrate;
• one or more light-emitting units each comprising a light-emitting element and a first thyristor;
• a first electrode to which a first voltage is applied for light emission of the light-emitting units;
• and
• one or more second thyristors that permit the light-emitting element to emit light by a second voltage that is lower than the first voltage and set irrespective of the first voltage, wherein:
• the light-emitting units each include one or more light-emitting elements;
• the second thyristors correspond to respective ones of the light-emitting units;
• both of the light-emitting units and the second thyristors are on the substrate;
• the second thyristors are between a member that supplies the second voltage from outside the substrate and the light-emitting units on the substrate;
• and
• further comprising a terminal that supplies the second voltage for each of the second thyristors corresponding to the light-emitting units, wherein:
• the substrate has a first side surface and a second side surface that face each other and a third side surface and a fourth side surface that connect the first side surface and the second side surface and face each other;
• the member that supplies the second voltage is on the substrate adjacent the first side;
• and
• the terminal is on the substrate adjacent one or both of the first side surface and the second thyristors, which are adjacent the third side surface and the fourth side surface .