user27363: I have ldr module with 4 pins
 1. Vin
 2. Gnd
 3. AO
 4. DO
I want to know how can i take advantage of DO suppose i want to turn on lcd display when light falls on the ldr sensor! 

I have noticed when light falls on ldr sensor the Green  led with DO written next to it lights up.

user4143: The DO pin gives a Digital Output that is HIGH when the light falling on the LDR is above a threshold, and LOW when it's below a threshold. Just connect it to a digital input pin and read that pin with digitalRead(). 
You can change the threshold by adjusting the small blue trimpot.

27363: <p>I have ldr module with 4 pins
 1. Vin
 2. Gnd
 3. AO
 4. DO</p>

<p>I want to know how can i take advantage of DO suppose i want to turn on lcd display when light falls on the ldr sensor! </p>

<p><a href="https://i.stack.imgur.com/5RUeE.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5RUeE.jpg" alt="enter image description here"></a>
I have noticed when light falls on ldr sensor the Green  led with DO written next to it lights up.</p>
 4143: <p>The DO pin gives a Digital Output that is HIGH when the light falling on the LDR is above a threshold, and LOW when it's below a threshold. Just connect it to a digital input pin and read that pin with <code>digitalRead()</code>. </p>

<p>You can change the threshold by adjusting the small blue trimpot.</p>
