LDR sensor to be used with a led lamp

[KhaledOsmani]

Hi,

I want to build a circuit, mainly consisting of an LDR, that when senses "complete" dark, the circuit acts as closed switch and the lamp would glow.
The degree of darkness shall be regulated using a pot.
The purpose of this, to make a visible path at home when electricity cuts off.
Any such ldr circuits?

 

[malik_zohaib]

use op-amp as voltage comparator.

 

[betwixt]

In it's simplest form, you use a single transistor with the lamp in it's collector. You provide enough base current through a fixed resistor to turn the transistor on and the lamp lights. An LDR has a resistance that drops when light falls on it so wire it between the transistor base and ground. In daylight the low resistance will pull the bias current to ground and turn the lamp off, in darkness it will have no effect so the lamp will light.

Actual values depend on the voltage and how much current the lamp passes and the LDR characteristics of course.

I have just built a unit for my home that turns battery powered lights on when the main electicity fails but only if it is also dark outside.

Brian.

 

[KhaledOsmani]

In it's simplest form, you use a single transistor with the lamp in it's collector. You provide enough base current through a fixed resistor to turn the transistor on and the lamp lights. An LDR has a resistance that drops when light falls on it so wire it between the transistor base and ground. In daylight the low resistance will pull the bias current to ground and turn the lamp off, in darkness it will have no effect so the lamp will light.

Actual values depend on the voltage and how much current the lamp passes and the LDR characteristics of course.

I have just built a unit for my home that turns battery powered lights on when the main electicity fails but only if it is also dark outside.

Brian.

schematic available?

 

[D.A.(Tony)Stewart]

are you sure you want to detect darkness or loss of power or both?

The key aspects require the light sensor to be blocked from light from the LEDs and battery backup.

 

[mar0791]

do you want emergency lighting? This switches on , when electricity in home cuts off ?

 

[betwixt]

schematic available?

specification available?

I repeat: Actual values depend on the voltage and how much current the lamp passes and the LDR characteristics of course.

What I described is the simplest possible scenario, there is no point in me showing a schematic unless you can specify the voltage it works on and the current drawn by the lamp. I can guess as LDR characteristics as they are all similar but the lamp could be anything between a red indcator LED and a halide floodlight, 1.6V DC @ 1mA or several hundred volts AC @ several Amps.

Brian.

 

[Audioguru]

You can make a circuit where a transistor lights an LED and an LDR turns off the transistor and LED when it is lighted.
A big problem with it is that LDRs have a wide range of resistance with a certain amount of light so some will work and others will need a lot of light to turn off the transistor.

Why doesn't your government fix your electricity system so that it is reliable? It should be upgraded so that they do not need to cutoff areas for "load shedding".