We found this circuit in a 1964 Electronic Design. The triac and SCR can be replaced with modern equivalents according to the load. The circuit is for 160V network.
With this circuit it is possible to keep the current in an LED constant even if the supply voltage...
This circuit was suggested by Motorola in its manual of components for optoelectronics (1987)...
This sensitive circuit can be designed with FETs such as BF245 and MPF102. The sensor is a silicon...