Light Level Indicator Using a Window Comparator

The second example below uses a LDR (light dependent resistor) to indicatesome desired light level. The LDR has a large dynimic range and varies inresistance from less than 100 ohms on a cloudy day to over a megohm in totaldarkness. A 2K pot was used to adjust the window range for usual room lightconditions. This setup might also be used to indicate sunrise/sunset conditions.

Light Level Indicator Circuit Diagram

Light Level Indicator Circuit Diagram

The proto board picture below shows the circuit wired to measure lightlevel using a LDR and 2K potentiometer. The green (window) LED is litindicating the light level is about right to take the picture.


Indicator Circuit Diagram

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