It might be suggested as a solution of this problem that lamps of different voltages could be used. 弗兰克·刘易斯·戴尔.爱迪生的生平和发明.
For example, the simple voltaic cell and the gravity cell have approximately equal voltages, but the current produced by the voltaic cell is stronger than that produced by the gravity cell. 伯莎M.克拉克.科学通论.
But two voltages of equal value do not give equal currents unless the resistances met by the currents are equal. 伯莎M.克拉克.科学通论.