How to get lock screen option in Lubuntu?

I am using Ubuntu 12.04 with many DE. Lubuntu is one of them. I don't have any option to lock screen in Lubuntu while I do in Unity and other DE.

Is there any program / application that I can install in order to lock screen in Lubuntu?

I just use the keybindings I've always used on ubuntu. Press: Ctrl + Alt + L

Should work

There is an article at the here at the LXDE forums. It gives instructions on creating a .desktop file to lock the screen, and adding it to the top panel.

The lxlock program provides screen locking functionality in LXDE.

It is part of lxsession. The lxsession package provides it.

Try running lxlock from the Run dialog (Alt+F2 or LXDE Menu > Run) or the LXTerminal (Alt+F2).

If lxlock locks the screen, you can work around the problem by running it that way or by creating a launcher for it on the menu, panel, or desktop.

If lxlock runs but does not lock the screen, that's probably a bug.

If lxlock is not present on your system, run this to install (or, if it's installed but damaged, to reinstall) the lxsession package:

sudo apt-get update && sudo apt-get --reinstall install lxsession

After installing that, lxlock should work, but if it runs and fails, try logging off and back on to see if that helps.

Try installing lubuntu-default-settings package. Open a terminal and run this command:

sudo apt-get install lubuntu-default-settings

This should fix the problem.