Pressing F3 (you can change the key) you can spawn a light attached to your right arm, press the key again to delete the light...
When you are carrying the light you will not be able to shoot (itīs a problem that I canīt fix because I tried to make the light donīt collide with Niko but if the light donīt collide will not stay attached to Nikoīs Right Arm)...
In future versions of Script Hook maybe Iīll be able to fix it, but now, the only bones avaible to attach objects are the Head and Right Hand...
You need GTAIV .NET Script Hook V0.86 BETA...
Download the latest version here: http://www.gtaforums.com/index.php?showtopic=392325 ...
Have you considered using native calls to the engine to fix the placement of the light, that's what i had to do for some of the functions of my script.