Level 5 corresponds to a light brown on the universal colorimetry scale (1 = black, 10 = lightest blonde). It measures the lightness or darkness of hair, independent of the reflect.
The golden (.3) reflect adds warmth and luminosity. It creates a sun-kissed, natural effect that flatters warm skin undertones. One of the most requested reflects because it adds dimension and shine without being excessive.
Each brand codes level and reflect differently. The table above shows how the major professional brands name this same shade: level 5, golden reflect.