2.1 Introduction

Daylighting is an important element that needs to be considered more during building design. Many research claim that it allows flexibility in the façade design and can enhance more efficiency in terms of energy and usage of artificial lighting (Li et al, 2002). Recently, numerous papers and articles have been written about the importance of daylight, by explaining the benefits and how new technologies can maximize the implementation of daylight in the early stages of design. This chapter will focus on the definition of daylight, its benefits and principles that can allow assess to daylight in buildings.

2.2 Definition of Daylight

Natural light, or daylight is considered all direct, diffuse and reflected light from the sun during the day. It includes sunlight (directly from the solar surface), skylight (clear sky cloudy or overcast sky) and sunlight/skylight reflected from other surfaces such as buildings, the ground or other bodies of water (Steffy, 2002). Daylighting can be defined as the practice of using daylight as the primary source of illumination in a room or building (Ternoey, 1999). Physically, the light of sun is a source of electromagnetic radiation with a balanced spectrum of colors ranging from ultraviolet 100nm to infrared radiation 10nm(SITECO an Osram Business, 2011). But only a small part of this light is visible for human eyes, range between 380nm to 780nm(Tregenza and Wilson, 2013). The characteristics of daylight involves a