Red low intensity obstruction lights are usually used for tall structures less than 45m above ground level as top lights. For structures over 45m, multiple low intensity obstruction lights are used on intermediate levels to mark the structure’s outline along with medium intensity obstruction lights. Medium intensity obstruction lights are usually used for tall structures more than 45m above ground level. According to ICAO obstacle lighting standard (Edition July 2018), There are three types of medium intensity obstruction lights: red flashing 2,000cd±25%, red steady 2,000cd±25%, white flashing 20,000cd±25% at day, 2,000cd±25% at night.