741 Based Light Sensor:  CdS photocell used for light/dark controlled relay

Basic   Infrared Light   Train Detection:

Battery Powered Sensor Detects Dangerous U Volt Radiation: 12/08/94 EDN-Design Ideas 

Block Occupancy Detector Helper:

Dark / Light Activated Relay:

Dark Activated Switch or Porch Light Switch:

Darkness monitor :

Day and Night Infrared Detection:

Demodulator Makes Low Cost Optical Tracker: 06/18/98 EDN-Design Ideas

Infrared to Light Converter: This circuit converts infrared light into sound. Modulated Infrared light, like that ROM remote controls, Infrared received by the phototransistor and is amplified by the LM386 IC.

Laser Pointer Train Detector:

Latching light detector is frugal with power and parts: 09/26/2002  EDN - Design Ideas / This idea demonstrates three uses for the humble LED. The circuit in Figure 1a forms a simple light detector that latches and turns on an LED when the ambient light exceeds a preset limit determined by potentiometer P1. LED D1 is both the indicator.

Light / Dark Detector:

Light Detector #1:

Light Detector #2:

Light Direction Sensor:

Light Intensity Sensor: Logarithmic amplifier uses the log caracteristic of PN (diode, transistor) to implement logarithmic function. The second transistor is used as refference and with the PTK resistor minimizes the dT/dV coeficient.

Light Pollution Meter : LED brightness control circuit and a multimeter to compare light levels to LED level.

Light Sensing RF Transmitter:

Light Sensor Adapter for Oscilloscope:

Light Sensor With Hysteresis:

LIGHT/DARK ACTIVATED RELAY: This is actually two circuits a light activated relay being the first and a dark activated relay being the second, once again all components and values are displayed in the gif image.

Matched Diode Pair Improves Performance Of Linear Optical Sensor : 05/27/02 Electronic Design - Ideas for Design / Hand-marked cards for applications like voting machines and meter readers often have dark marks, light marks, erasures, or dirt. Digital systems can't distinguish between an intended mark, dirt, or erasure because they have a single preset threshold....  

Optical sensor needs no tweaking: 06/13/2002  EDN - Design Ideas / The transfer gain of optical sensors spans a 16-to-1 ratio because of variations in the LED, phototransistor, ambient temperature, and optical path. The wide transfer-gain variation complicates output-resistor selection in dc-coupled circuits. You must size the output resistor to prevent high transfer gains from causing output-stage saturation, but low transfer gains yield low output-voltage sw....

Photodetector Sorts Objects: 03/04/99 EDN-Design Ideas / PDF contains multiple circuits - scroll to find this circuit.

Programmable Light Activated Relay:

Pulsed Sensor Extends Battery Life: 01/01/98 EDN-Design Ideas

RF Transmitter, Light Sensing:

Solar sun tracker :

Two LEDs Perform Rudimentary Spectral Analysis: 09/01/94 EDN-Design Ideas

U Volt Sensitive Photodetector:

Using The LM555 Timer With Photocell Detectors:

Visible Light Photo Detector Circuits (E+F):