ICAO Annex 14 regulation, for unmarked structures (unpainted with white / red horizontal bands), prescribes the use of Aircraft Warning Lights both for day and night operation.
Appendix 6-6 of the standard indicates the use of flashing white high intensity warning lights during day time (200.000cd), twilight (20.000cd) and night time (2.000cd) to be installed on several levels (for buildings from 150 meters up).
If an aeronautical study or the civil aviation body under which the control of the structure in question falls, decides the use of other lights or other configurations, the prescriptions must be respected by way of derogation from the ICAO standard Annex 14.