It's by opposition to Night VFR (NVFR) which allows to fly by night in visual meteorological conditions. So the answer will focus on NVFR, rather than on day VFR.
EASA harmonization over EU countries is done by enforcing Standardised European Rules of the Air (SERA). SERA states that a night flight must be conducted in IFR, and therefore the crew must hold an Instrument Rating.
Prior to SERA, some countries did not allow VFR at night for security reasons (aircraft not visually identifiable, and no transponder), but other did, that's the case for the UK that I'll use as an example here.
When implementing SERA, EU countries can use acceptable means of compliance, as described in ED Decision 2013/013/R and its annex.
- NVFR is implemented (or denied) in EU country by country. So rules may differ between countries. UK example:
- UK license can be extended for NVFR.
- More for UK NVFR: Safety Notice: SN-2012/007.
- In practice, VFR at night is permitted in accordance with SERA requirements. Aircraft leaving the vicinity of an aerodrome must maintain 2-way communication with ATC and file a flight plan. The process of 'booking out' is still accepted as an alternative method to filing a formal paper or electronic flight plan in certain circumstances. Similarly, abbreviated flight plans filed in flight are still permitted. There are also more restricting weather minima:
- Minimum cloud ceiling of 1500 ft AMSL
- Flight visibility of 5 km, or 3 km in the case of a helicopter flying outside controlled airspace
- Maintain sight of the surface when flying at 3,000 ft AMSL or below
- Minimum height of 1000 ft (or 2000 ft if over high terrain) above the highest fixed obstacle within 8 km of the aircraft except when taking off or landing
- Night is defined for this purpose:
- Aircraft must be compliant for NVFR, e.g. this equipment is required:
- artificial horizon
- Instrument Lighting
- Landing Light
- Position and Anti Collision Lights
In countries where NVFR is not allowed, IFR applies at night.