Which sensor to detect light? I have a kit of 37 sensors as described here:


http://www.instructables.com/id/Arduino-37-in-1-Sensors-Kit-Explained/?ALLSTEPS
https://tkkrlab.nl/wiki/Arduino_37_sensors


I want to create a simple circuit:


if the light is detected - flash LED
if there is no light - do nothing


Among 37 sensors I don't seem to find anything related to light / brightness / lumens...

Can you please advise me which sensor to get? 



Shall I get a photocell  (Light Dependent Resistor) as described here: https://learn.adafruit.com/adafruit-arduino-lesson-9-sensing-light/parts ?
Number 23 in the list says photoresistor, corresponding to module KY-018 in your kit, which is what you called photocell (a photocell is another type of sensor to my knowledge).
As the name states, a photoresistor is a device changing it's resistance depending on the amount of light it detects/receive.

A photoresistor usually looks like:


In order to get a meaningful reading from an LDR you need to convert the resistance into a voltage which the Arduino's ADC can read. The simplest method is to use a voltage divider: the junction between the LDR (photoresistor) and R1 is the node to connect your analog pin to get your readings, which will be a voltage that is a proportion of the supply voltage (5V) defined by the ratio of the two resistances.

The KY-018 module mentioned above already provides all the necessary and provides you 3 pins: 5V, ANALOG and GND.







simulate this circuit &ndash; Schematic created using CircuitLab