Refer to diagram: Switch “SI” is in the “on” position. Light “LI” does not come on. Voltage across “SI” is 120 volts. Voltage across “LI” is O. What is the problem?

Refer to diagram: Switch “SI” is in the “on” position. Light “LI” does not come on. Voltage across “SI” is 120 volts. Voltage across “LI” is O. What is the problem?