exceeding for example 36 volts is applied across pins 75 a and 75 zener diode 125 will conduct and a voltage of approximately 0 7 volts will be applied to the base of transistor 90 as a result transistor 90 will be turned on and will conduct current form its collector to its emitter this condition will result in no voltage being applied to the base of transistor 80 thereby causing it and transistor 85 to be in an off non conducting condition led 120 is thus protected from the harmful transient voltage as substantially no current will flow through it in this condition alternatively the circuit may be arranged to provide only a safe level of current to flow through led 120 under transient voltage conditions as will be appreciated led protection circuit 70 may be used to provide protection to leds from transients in both 12 volt and 24 volt electrical system vehicles in the led protection circuit 70 zener diode 125 and transistor 80 85 and 90 form part of a first switching mechanism that allows safe level source voltages to be applied to the remainder of the circuit to provide a current for led 120 in a first switching condition shunts away harmful level source voltages and prevents them from being applied to the remainder of the circuit in a second switching condition in addition when the safe level voltages are applied to the remainder of the circuit zener diode 140 and transistor 95 act as a second switching mechanism that causes a safe below the maximum operating current current to flow through the led 120 regardless of the actual voltage level of the source voltage e g 12 volts or 24 volts as noted above all of the circuit elements shown.