The energy efficiency of the Philips Hue White & Colour Ambiance (GU5.3, 6.30 W, 400 lm, 2 x, G) with a "G" rating seems counterintuitive for an LED light source that is normally very energy efficient. Here are some possible reasons:

- EU energy efficiency labelling: EU energy efficiency labels are based on specific criteria and tests that take into account not only the efficiency of the light source itself, but also other factors such as overall system efficiency and compatibility with various devices. It is possible that the "G" rating is due to these broader criteria, rather than just the efficiency of the LED chip itself.
- System requirements: Philips Hue bulbs often require a connection to the Hue Bridge or other devices, which can mean additional energy consumption. These system requirements could be factored into the overall energy efficiency rating.
- Specific test conditions: The EU energy efficiency labels are awarded under standardised test conditions. It could be that the specific test conditions under which the light source was tested resulted in a lower rating.

It is important to note that LED light sources are generally very energy efficient, but the EU rating systems may take into account more complex factors that result in a lower rating. For precise information, I recommend consulting the manufacturer's official documentation or the EU directives on energy efficiency.