Light Science and Technologies (Photonics) now touches almost every area of our lives. It is considered a Key Enabling Technology (KET) or an Essential Technology for the development of Europe, USA and others main nations around the world. Photonic Sensing is understood as any sensing approach that employs light technologies and it is becoming an area with very important expectations of annual growths and strong socio-economic impacts in the present decade of this XXI century. In this tutorial, will be offered a Doctrinal Conception of Sensing using Light (SuL) as an “umbrella” in what any sensing approach using Light Sciences and Technologies can be easily included. The key requirements of a sensing system will be, easily, introduced up to reach the general conception of a sensor using light techniques and related issues such as its main constituted parts and types. The case in which smartness is conferred to the device it is also consider. To illustrate this general concept, a quick “flight” over significant cases using different principles, techniques, technologies to detect diverse measurands in different sector applications such as Civil Engineering, Industrial Processes, Energy, environmental Health and Medicine, among others will be offered. Finally, some words concerning expected market and challenges to face in the near future will be also addressed. After this tutorial, any sensing approach using Light Sciences and Technologies will be easily and properly included in the umbrella of this key area both of sensors and of photonics: Sensing using Light or Photonic Sensors.