Matches in the preliminary round, round 1 or round 2 may be played in daylight or under floodlights. If played under floodlights, the illuminance must correspond to the requirements set in the UEFA Stadium Infrastructure Regulations.
From the group stage onwards, matches must be played under floodlights with an average horizontal illuminance level of at least 800 Eh (lux) and uniformity ratios of U1 > 0.40 and U2 > 0.60. The average level of vertical illuminance must be at least 350 Ev (lux). Glare ratings (RG) must be less than 50 and pitch illuminance levels should have a colour rendering (Ra) of at least 65.
From the group stage onwards, an independent backup power supply must be available and able to provide at least 350 Eh(lux) horizontal illuminance, to ensure that matches can proceed in the event of a power failure.
Clubs must ensure that the stadium floodlight system is regularly maintained to meet the minimum illuminance values as outlined in the paragraphs above and proven by a lighting certificate issued no more than one year prior to the date of the club’s first match and valid for the entire competition period. UEFA may conduct an independent assessment of lighting levels in stadiums and will notify the clubs in good time of the results of such assessments and of any corrections to be made.
Full floodlighting must be provided for training sessions the day before the match and from two hours before kick-off, unless it is required earlier for operational purposes (e.g. calibration of goal-line technology). Furthermore, the use of LED floodlight entertainment (light show) may be permitted according to the principles determined in the UEFA Stadium Entertainment Lighting Guide. Any such use may only take place either before the warm-up, between the warm-up and the players leaving the tunnel for the match, or after the match. Exceptions may be agreed with UEFA in specific circumstances (e.g. during a moment of silence).