This is one of the many versions of this type of indicator that the reader can find on our website. This is from Mullard's 1969 documentation. The indicator is 95 uA (100 uA).
Using power transistors of the time, this source was published in Radio Electronics magazine in...
The network formed by resistors and capacitors determines the frequency of this sinusoidal...
The sensor in this circuit is an LDR and the potentiometer serves to control the sensitivity...