**Preface to "Optical Technologies Applied to Cultural Heritage"**

Art and optics have in common one of the most difficult materials to work w ith: l ight. Optics and art cannot be understood without light. Light has accompanied humans from the beginning of time. Light allowed human beings to create habitable spaces in places not reached by sunlight. Family, culture, magic, all of them were possible thanks to light. Fire (heat and light) let those early societies be heated, cook food, and have better relationships among individuals. This essential role is shown in many legends from the early stages of human history. For example, Gilgamesh's trip is a metaphoric journey from darkness to light, or even in the Genesis God said:

"Let there be light," and there was light. God saw that the light was good, and he separated the light from the darkness.

Nowadays, light has the same magical power as in those old times: it allows us to know what is beyond our eyes' reach. Scientists from all around the world are changing the way we see nature and cultural heritage. They push the cutting edge of optics further, and this permits us to deepen our knowledge and understanding of artistic goods, apply better preservation technologies and open a window to a wide range of unknown possibilities where imagination is the limit. Light technology makes it possible to obtain extraordinary information about our universe, travel in time and read information that was hidden in the stars, which the history of cultural heritage is and how to restore and preserve this heritage. Like the lighthouse of Alexandria, a mythical construction whose creation was ordered by Ptolemy II (II BC) and was used to guide sailors to find t he right way into the harbour with a beacon light, the latest optical technologies enlighten to us to make the best decisions regarding how to preserve, restore and make it possible for people to access and enjoy cultural heritage. At the same time as science and technology are changing more and more quickly, cultural heritage is increasing its significance a nd i mportance i n s ociety. I t i s a p aradox h ow the oldest and most constant agent gets a progressively more important role in societies where everything changes very fast. Simultaneously, new technologies are developed every year, which enable us to know better and deeper our cultural heritage. The changing world generates a strong need for a sense of belonging and cultural stability in all human beings around the world, but this sense can be more easily obtained by means of these new technologies due to their impact in cultural heritage preservation and exhibition. When we talk about cultural heritage, we refer to very different artefacts and relics with different conditions, shapes, forms, status, etc. It must be considered that cultural heritage includes artefacts, monuments, buildings, sites, museums, industries, and even intangible goods, and they have a diversity of values like symbolic, historic or aesthetic. With such a casuistry, the appropriate technology for each one cannot be the same. Restorers now have many technologies at their disposal, and more of them coming from optical technologies, but this was a chimera only 20 years ago.

All these new actors that appear around the restoration work require a close relationship among experts from both worlds: science and arts. It is necessary to find new spaces where these two sides of cultural heritage can meet and work together. It is not an easy task, and it requires spaces to share relevant information of both worlds, optics and cultural heritage. This is mainly the scope of this book, which contains important contributions that we hope will be useful to improve the knowledge, understanding and valuation of this area.
