Found in a 1960s RCA documentation, this circuit applies to most common triacs. The trigger device is a neon lamp and the sensor is an LDR. R is typically 100k and C is 220 nF.
Suggested by General Electric in a 1970 document, this circuit uses a LASCR, or SCR fired by...
This circuit was found in February 1976, Radio Electronics magazine. The circuit is powered by 12 V...
This circuit uses LDRs as sensors and can either detect the incidence of light on the sensor or...