In order to comply with the Regulation (EU) 2019/2015 the important thing is to make sure that light sources are accompanied by a label in line with the specifications under Annex III. The requirements for the labelling of light sources do not necessarily impose packaging. In this respect and for each light source which is placed on the market as an independent product (i.e. not in a containing product) and in packaging, the label shall be printed on the individual packaging, in the format set out in Annex III.
Given that Article 4 (e) of the 2019/2015 Regulation also refers to labels on light sources attached to the packaging, the possibility to join or fasten the label to the packaging in a stable way exists. This could include sticking the label to the package.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.