how to put that script please give me instruction

@AlessandroB .. Thank you very much .. you saved me alot of search time

This thread is about Unity, not native SDK.

Anyway, if you check the API reference, you'll see that you can use the setFlashTorchMode() method of the CameraDevice class.

https://developer.vuforia.com/resources/api/class_q_c_a_r_1_1_camera_device

What if I'm using the native SDK with eclipse, not unity

can I turn the flash light ON/OFF through it ?

Add it to a script that inherits from MonoBehaviour and then drop that script on to the ARCamera.

where input the code? brother...

Thanks for your help, now my flashlight it's work

Here you go..

        // Turn flash on or off.
        if (GUILayout.Button("Toggle Flash", buttonGroupStyle))
        {
            if (!mFlashEnabled)
            {
                // Turn on flash if it is currently disabled.
                CameraDevice.Instance.SetFlashTorchMode(true);
                mFlashEnabled = true;
            }
            else
            {
                // Turn off flash if it is currently enabled.
                CameraDevice.Instance.SetFlashTorchMode(false);
                mFlashEnabled = false;
            }

            mMenuToShow = MenuMode.MENU_OFF;
            mButtonPressed = true;
        }

That code can go in the OnGUI method of a script that inherits from MonoBehaviour, and you also need to add the following member variable to store the state of the flash so that it can be toggled..

    // Check if flash is currently enabled.
    private bool mFlashEnabled = false;

The button style can be defined as such..

        // Setup style for buttons.
        GUIStyle buttonGroupStyle = new GUIStyle(GUI.skin.button);
        buttonGroupStyle.stretchWidth = true;
        buttonGroupStyle.stretchHeight = true;