I have connected Relay 4 channel with Arduino Uno and while running the application it was showing on and off of the Relay LED but it is not controlling the bulb on and off. what can be the cause for this?
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hand draw a wiring for the way you put power to the bulb.
the relay only acts as a switch, it is not a power source.
as noted, we need more information.
I see no faulty diagram, no faulty code, no bad version of relay….
Its basic relay program. Please find below.
#define RELAY1 7
void setup()
{
Serial.begin(9600);
pinMode(RELAY1, OUTPUT);
}
void loop()
{
digitalWrite(RELAY1,0);
Serial.println("Light ON");
delay(2000);
digitalWrite(RELAY1,1);
Serial.println("Light OFF");
delay(2000);
}
Pin Setting:-
Arduino Relay
Pin7 IN1
5v Vcc
GND GND
After connection Relay LED is blinking, but the bulb wont react the same.
Connection:-
Power supply to COM
supply line to Light connected to NO
Hope this helps.
Can we get a link to the relay board specs?
Are there any jumper-plug options on the relay board?
Do you hear the relay clicking?
Do you have a multimeter to check the relay contacts? (Check the on/off resistance without power or the lamp connected.) If the relay is not switching it would also be helpful to check the coil voltage.
Does the light come-on when you connect the wires (bypassing the relay)? Of course, "be careful" if that's power line voltage. Or if you connect to NC instead of NO, does the light stay on?
Connection:-
Power supply to COM
supply line to Light connected to NO
COM and NC are OK, but can we see a schematic? (Hand drawn is OK.)
Do you hear the relay click? What power supply for light? How much current / voltage for light?
Is it possible to use code tags, </>, when attaching code? Found in the Quick Reply header to the very left.
kdutta:
Connection:-
Power supply to COM
supply line to Light connected to NO
JCA34F:
Do you hear the relay click? What power supply for light? How much current / voltage for light?
Guys, missing the point here!
What is the OP using to power the Arduino and relay module with the necessary 5 V? (Presumably it is a 5 V relay board.)
Note the requirement for 5 V, not any other voltage!
No photograph of the set-up provided, makes the discussion much more slow and tedious. 
kdutta:
Connection:-
Power supply to COM
supply line to Light connected to NOHope this helps.
well, it does not really help.
we have to assume that your code is perfect and your Arduino is perfect.
that then, leaves the relay. there wire, the power supply and the lamp
since the relay needs a signal.. we have no clue what it is getting
if the relay clicks when called, seems someone asked that.... then the relay is working.
if you send your 5 volt power to your relay COMM and connect your 120 volt light to NO
and do not connect ground... well, the circuit is not complete. but, just guessing here
shame no one thought to ask you to make simple sketch.
or list the lamp,
or what votlage it is
or what voltage the power supply is
or if the relay clicks
the thing that will make you laugh is how silly the answer is.
I'm guessing it is the red wire. it is either connected wrong, or missing altogether.
Hi,
Welcome to the forum.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Can you please post a picture of your project so we can see your component layout?
How are you powering the project?
Can you post a link to data/specs of the 4ch relay pcb?
Thanks.. Tom... 
kdutta , yes, WELCOME to the Forum.
It seems that you are finding out the hard way that we cannot guess with things.
the simplest detail can make all the difference.
this is some odd rule of the universer that relates to speed of answers is inversley proportional to information.
since you have a 4 relay module, we can assume that it works, that you put the jump on it the right way, and that when your sketch sends a signal to it, that the relay you want to us, makes a loud clicking noise.
and than when you invert the signal, that there is a second loud clicking noise.
if you are getting that loud clicking noise, then half of the hardware and all of the software is put into the 'working' category and we do not need to talk about that.
that leaves the power supply, lamp, relay and how things are wired.
if, however, you do not get that loud click, we cannot rule out that :
there may be problems with the power supply, lamp, relay and how things are wired....
but, that the immediate problem is that the relay is not responding.
so, question #1) does the relay click when you send it a signal ?
Check the voltage at coil of relay first at ON and OFF state, it should be match to the rating of relay circuit. Provide circuit diagram to guide better.