Light Arrows are an ammunition type in Demon's Souls.
The Light Arrow is an improved version of the normal arrow, having increased range with otherwise identical stats. It is, however, somewhat expensive. If the souls can be spared, then this arrow is highly recommended to be used as the go-to arrow of any archer.
The increased range also causes lower damage drop off, allowing more damage to be done on mid-range shots. The arrow will also fly in a straighter line, allowing for enhanced accuracy.