Definitions of Light

I efteråret 2015 udstillede Teknologihistorie DTU i Bygning 306. Udstillingen afsøgte grænsen mellem installation og kulturhistorisk udstilling i et forsøg på at komme nærmere menneskets mange anvendelser og definitioner af lys. I udstillingen var der også mulighed for at selv at bidrage med egen definition af lys. Bidragene blev indsamlet og er nu postet herunder.

Exhibition on display in Building 306 during Fall 2015. What is light? Balancing between the traditional cultural exhibition space and the art installation the exhibition encouraged the user to consider what light is – how we as humans use light, think of light and work with light. The exhibition became complete with the contribution of the users – how did they define light? The contributions was collected and is now posted on this website. 


2015 International Year of Light

UN General Assembly has declared 2015 as International Year of Light and Light-based Technologies. The aim is to bring global attention to the importance of light and optical technologies in a sustainable future.  

Ancient Greece philosophers contemplated the mechanisms of sight. Did the light originate in the eye or come from the object, you were looking at – or perhaps both? They did not really have theories about the nature of light in itself.


From early religions to the modern day Star Wars light is often used as a symbol of the good and virtuous while darkness symbolizes evil.

Learn more about religious festivals of light:


Albert Einstein proposed, that eletromagnetic radiation consists of quantas. This quanta was later coined ‘photon’. And 100-years ago he placed light centrally in the theory of General Relativity. Is light the primary component of the physical universe? Find out more about the Einstein Centenary here:

Light amplification by stimulated emission of radiation - or as we know and love them Lasers. The basic function of lasers is to take a small amount of light and ‘’multiply’’ the amount by means of stimulated emission, giving much higher power


Finsen lamp treatment 1925

In 1903 Niels Finsen received the Noble Prize “in recognition of his contribution to the treatment of diseases, especially lupus vulgaris, with concentrated light radiation, whereby he has opened a new avenue for medical science". Finsen used arc light, which he called chemical rays

Learn more about Finsen here (in Danish, sorry…) all about energy, and light is the strongest manifestation of energy. In fact, the light in your home - both natural and artificial lighting - greatly influences the quality of your home energy - the feng shui of your home 

Could it be a candidate for the Nobel Prize?!

In 1999, the Danish Physicist Lene Hau Vestergaard slows down the light by sending it through temperature close to the Absolute Zero.


The 2014 Nobel Prize was given to I. Akasaki, H. Amano and S. Nakamura for the invention of the blue LED, the fundamental technology behind all modern high efficiency LED lighting. The blue light from the LED is used to excite a phosphors coating on the LED which gives the white light


Who needs light anyway?

Not all living things need light. Some very pale animals living at the bottom of the oceans by the hypothermal vents feed of bacteria that use the toxic hydrogen sulfite leaking from earth. Together with oxygen and carbondioxid from the water the bacteria are able to survive. Eating the bacteria the animals are capable of surviving in total darkness. But don’t dissect these animals without covering your nose – their diet makes them reek of rotten eggs.

Christiaan Huygens formulates a detailed wave theory of light. Here’ the short version of his life:


And God said, Let there be light: and there was light.

And God saw the light, that it was good: and God divided the light from the darkness.

And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.

Quantum Mechanics resurrects an old conflict

What is light – wave or particle? This old conflict reappears with the arrival of quantum mechanics in the early decades of the 20th century. In 1965 American physicist Richard Feynman states: “We choose to examine a phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery.”

“Light does not spread immediately but travels with a definable speed!” boldly claims the Danish Astronomer Ole Rømer after spending a year observing and timing the eclipse of Io (the innermost big moon of Jupiter) by the shadow of the planet.  In 1676, the Danish astronomer Rømer announces his explanation of the Io eclipses in a lecture in Academie des Sciences.Do you want to see his instruments? They are at Kroppedal Museum just outside Copenhagen

Islamic scholars debate eyesight and use new technology to demonstrate that light travels in straight lines. Ibn al-Haytman states, that the eye is a passive receiver of light reflected by objects. The works of these scholars enter into the European tradition through monasteries. 

Front page of the Opticae Thesaurus, which included the first printed Latin translation of Alhazen's Book of Optics

James Maxwell develops four equations for electromagnetism and postulates that light is just electromagnetic radiation, as are many other phenomenon. Find out more about the Long Road to Maxwell’s equations here: 

French philosopher-mathematician René Descartes has light moving as a pressure wave through a medium at infinite speed. Here’s what the great thinker writes between 1629 and 1633. Descartes delayed publishing this book after hearing that the inquisition convicted Galileo. This could lead to a warm and untimely death. Consider yourself warned…

“Less than 100 years ago, everyone could look up at a spectacular starry night sky. Now, millions of children across the globe will never experience the Milky Way where they live. Light pollution not only impairs our view of the Universe, it hurts the planet by increasing energy consumption, wasting money and harming the health and safety of humans and wildlife.” - International Dark-Sky Association

Why, isn’t this HYGGELIGT…The Danes are weird! – why do we light candles when it gets dark and not turn on some bright light so we actually can see what going on? Get the anthropologist’s take on this odd part of Danish culture (in Danish)

Miffed newton supports particles

In early 1670s Isaac Newton tells the world, that white light is made up of colours. Newton also supports the theory that light is made of particles, but other scholars criticise his reasoning. The sensitive Newton decides never to publish again. Humpf…

Around 1878, Thomas Edison invents a system of electrical illumination – and not just as is commonly thought the light bulb.

Citat: "We will make electricity so cheap that only the rich will burn candles” – Edison

Link: commercial for Edison Electric lights

Northen Light

Aurorae are caused by cosmic rays, solar wind and magnetospheric plasma interacting with the upper atmosphere (thermosphere/exosphere). Their charged particles, mainly electrons and protons, enter the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent light emissions. Incidental protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.

Light poverty

More than 1.3 billion people are trapped in light poverty, with no access to electricity

Sunbathing and the great outdoors were essentials for a healthy lifestyle in the vitalism movement starting in the 1890s. This probably inspired Pierre de Coubertin to resurrect the Modern Olympic Games in 1896. The work by artist J.F. Willumsen is representational for the ideas. Visit his work here: 

Are you SAD?

SAD - Winter depression 

The 6th Century scholar Jordanes describes the inhabitants of Scandza (Scandinavia) in the work Getica: In the north, there was the nation of the Adogit who lived in continual light during the midsummer (for forty days and nights) and in continual darkness for as long during the midwinter. Due to this alternation they go from joy to suffering. The sun moreover seemed to pass around the Earth rather than to rise from below.

DTU Contributions

lys er varmt og smukt. lys er glæde og hygge på kolde dage eller i triste tider. lys er elektronisk, fascinerende og mystisk

light is energy, happiness, waves, photons, rythm in days and nights

electro-magnetic waves and photons

at the basis of life

light matters

light is pretty light

light is light

light is a sparkle in your heart

field and wave electromagnetics

where my fear stops

it is better to light a candle than to curse the darkness - light is power. light is hope. light is life

not darkness

light is art and science at the same time

lys er godt

let there by light

because of light you and me can see

light is about love, family and kindness