Nominal Voltage DC is the designated vehicle-system voltage for which a product is intended, such as 12 V or 24 V direct current. It identifies the system class, not the full permitted supply range. See Input Voltage DC for the actual operating range. The nominal value is a convenient system designation rather than an exact voltage continuously present at the lamp. Charging systems, cable voltage drop, battery state, and operating conditions cause variation. Product compatibility should therefore be checked against both nominal voltage and the specified input-voltage range, together with relevant transient and polarity protections.