ECT 3 : Evening Civil Twilight. Period between sunset and total darkness, when it is necessary to use artificial light to carry out most activities. (Civil Contingencies Secretariat)
Joint Emergency Services Interoperability Principles JESIP (Working Together Saving Lives), Glossary (Common Language within Emergency Services - A Sub-Set of the UK Civil Protection Lexicon), UK 2015. http://www.jesip.org.uk/glossary/, (Emr Common Lang - Brit) {929}