A useful alternative to a series resistor is a series diode, or two diodes in parallel back-to-back. The diodes can be small-signal types and should be in a light-tight enclosure.

• 一个有用的方法是用一个串联二极管或者两个背靠背并联的二极管代替串联电阻。二极管可以为小信号的,必须为不透光的管壳。