I got a LED-torch kit. It drives 5 LEDs by a 1.5V-battery. CL0117, a boost chopper, applies a 1.5V-battery to the power for 5 of 3.1V-LEDs by coil surge. So I would like one spice to cook it, light-sensitive binary sensor. But if you want to make a switch by a transistor, you may meet dropping voltage on its Collector-Emittor because of building a buffer (common collector). It makes your boost chopper power-short for 5 LEDs. MOSFET? MOSFET can typically work on more voltage than 1.5V. 1.5V-battery is a little severe to light LEDs. If you use a relay, you may not meet dropping voltage in it.
1.5V-active-relay? Yes, it would be. At some hobby shop, I got a 1.5V-active-relay made by Matsushita (Panasonic). But, there’s a problem. The lower the coil needs its voltage to make active the switch, the more the current is needed. Because of less turns of wire, the coil has less resistance than coils with many turns of wire. How about heating of the coil? The coil heats more than coils with many turns. But, there’s one to fit my project in an experiment of a binary sensor. Besides, the clicking sound of switching in a relay is so cool.
See R3, a variable 100K Ohms Resistor, which is for adjusting the threshold to switch on/off of a binary sensor. A photoresitor changes its resistance by brightness beaming to it. Through combination of the variable resistor and the photoresitor, a binary sensor determines to switch on/off. Computer technology? Yes, binary sensors use in a analog-to-digital converter (ADC). But ADC typically uses a set of comparators which are made of many transistors to stay these stability against temperature, frequency, etc. If you want a study, check a point of switching on/off of your binary sensor, just above, in several situations. It may vary the point even though you test the same ratio of the resistance of the variable one to the photoresitor. A transistor has changes of its characteristics by temperature, frequency, etc. A comparator resolves this issue of a binary sensor which is made of few transistors.