The year of 2015, chosen to stage the UNESCO International Year of Light 2015, coincided with many anniversaries regarding history of the science of light and one of these was Fresnel’s Wave Theory of Light. Quite frankly there could be an anniversary for Fresnel each year for the next six years to celebrate one of his many achievements, each one equal to the magnitude of and stems from his wave theory.
On 10 March 2015, the Society of Light and Lighting (SLL) staged a large event at the Royal Institution in London, celebrating Augustine Fresnel’s life and work. It was sponsored by Philips, the International Association of Lighting Designers (IALD) and the STLD and included reconstructions of classic experiments and their modern counterparts, specially commissioned films and animations and showed artifacts. HRH The Duke of York and over 400 people attended it from the lighting industry. I was honoured to be given the opportunity to put the record straight of just how important Fresnel’s legacy is to everything we do with light.
My interest in him started from a young age. Whilst at school, I had a Saturday job in which I used Fresnel lenses for live professional shows. This lens that was lit by a pre-focussed filament lamp produced a soft edge beam. Later, when I was fifteen, my teacher, Roy Proudlove, taught me about how light behaves in great detail, as will be explained below, and nearly every aspect of this had the name Fresnel associated with it. I remember asking my teacher, (whose widow Jenny and his son were present at the lecture), the somewhat rhetorical question, was this the same Fresnel whose lens was used in stage lighting? I could not believe that one person could have achieved so much in his short lifetime. I have found that if you always keep his ideas in mind both the technical and aesthetic look of a lighting project will be correct. Unwittingly everyone reading this use his ideas all the time but it is rarely articulated. I wanted to put the record straight.
Augustine Fresnel was born in Broglie, France, in 1788, the same year as William Haslett and Lord Byron. His father Jacques, originally from Mathieu in the Calvados region and where Fresnel himself would grow up, worked as an architect and for many years oversaw renovations at the Chateau de Broglie where he met his future wife Augustine Mérimée of noble descent. He was the second of four brothers, Louis (1786-1809), a brilliant scholar who died young in 1909 whilst serving in the military in a battle in Jaca, Spain, and whose death intensified Fresnel’s hatred of Napoleon; Leonor (1790-1865) a polymath who is mentioned again later; and Fulgence a gifted linguist who translated ancient Muslim texts and histories of the source of the Nile and lead archeological surveys in Mesopotamia. His cousin Prosper Mérimée was a writer and was instrumental in early preservations of ancient monuments. For example, statues destroyed in WWII destruction of Reims Cathedral were replicated from Plaster casts that had been taken by Fresnel’s cousin over two hundred years before.
In 1801, aged thirteenth, Fresnel attended the l’Ecole Centrale de Caen and at 16 the Ecole Polytechnique where he was taught by his uncle Léonor Mérimée and then two years later he entered Ecole des Ponts et Chaussées where he met the scientist and his life long friend François Arago and was taught by Poisson and Legendre. He worked in the French equivalent to the UK Department of Public Highways, Ponts de Chausees where he designed projects such as a bridge at Ille-et-Vilane. At around the same time Napoleon returned from the Island of Elba and put royalist intellectuals under house arrest. It was then at 26 that Fresnel’s real passion for light really took off and would sustain his intellect for the rest of his life. He had been interested in fluid mechanics but when he read about the observations of Etienne Malus, that light is polarised when reflected and who had noticed, whilst walking past the Palace of Luxembourg, that the Sun’s reflection in one of the palaces windows all but disappeared when viewed through a ‘polarising’ crystal but not the view sun directly, leading to the Laws of Malus.
Fresnel’s early experiment was to study diffraction, the spreading out of light when it passes through a narrow aperture and the interference pattern observed when two such apertures are lit from a single source. Unknown to him at the time, was that Thomas Young at the Royal Institution in London, had done an almost identical experiment a few years earlier and had published his findings. When Fresnel discovered this he was really disconcerted, thinking he had missed-the-boat. But with the help of Arago, who spoke and could translate English well, he started corresponding with Young who encouraged him further. Fresnel had carried out his experiment with a modification to Young’s. As well as obtaining an interference pattern with two slits he used a very shallow pair of prisms, know now as a Fresnel Bi-prism, which produced two virtual lines of light, much brighter than Young’s method. The pattern produced from this could only be explained if the amplitude of light waves was perpendicular to the direction of travel of the light wave, i.e. a transverse wave. Not even Young had proposed that light was completely transverse. It seemed that those who believed that light was a wave, as the Dutch Scientist Huygens had proposed 150 years earlier, were gaining ground on others who thought light as being particulate in nature. Fresnel went on to explain a phenomenon that had baffled even Huygens, Newton and many others. A property that some materials like Iceland Spar, now called calcite, refracts (or bends) in such a way as to produce two rays. The first is the ordinary ray, which refracts in the same way as in any transmitting material. The extraordinary ray, that refracts differently depending on the angle that the light enters the material, Fresnel described by relating it to the polarization that occurs with the direction of the wave through the material leading to a changing in its refractive index that occurs which is in turn caused by the material not being ‘isotropic’ i.e. not being optically the same in all directions.
Fresnel rewrote the laws of reflection, modifying them so that as well as stating that for a specular surface, the angle of incidence equals the angle of reflection, he worked out that the magnitude of that reflection might be over 90% when the angle to the normal is high (grazing incidence) and as low as 4% at the normal and these values depended on the refractive index of the material. The lecture illustrated this by recalling the opening sequence of the 1960’s comic Harry Worth who used to stand at one end of a shop window, with one leg in the doorway out-of-site and lifting his other leg with the camera looking at grazing incidence. It gave the impression that he was lifting both legs as the reflection was so strong. Fresnel calculated the same efficiencies for refraction too, allowing us today to design lenses and optical systems with tremendous precision.
It was Fresnel’s deeper understanding and calculations regarding polarisation of light that allowed a thoroughly rigorous theory of it and would allow Lord Rayleigh to discover how light becomes scattered in the upper atmosphere and why the sky is blue and the Sun turns red as it sets as seen from the Earth or why we might see a blood-red moon during a lunar eclipse.
Of course, so far we have not even mentioned the famous lens that bears his name. This was really the main point of the lecture: to explain his other achievements. The lens was originally designed for use in lighthouses to create an intense beam of light to reduce the numbers of lives lost at sea. His brother Léonor, continued with the further use of Fresnel lenses in lighthouses after Fresnel’s death. If this was the single Fresnel had designed, we would still be celebrating him 200 years on, a laudable achievement in its own right. But it was not. In terms of his popularity, not his legacy, If the so called Fresnel lens, for he developed more than one type, was his No 1 selling 12 inch single, then his work on reflection, refraction, diffraction, interference between two diffracting images, birefringence and polarisation were his critical albums. The consequences of these are enormous today. The whole science of diffraction gratings, for example, first worked out out that our Sun is made mainly of hydrogen and helium (hence the name helium is from the Greek Helios meaning The Sun). The way in which light reflects off of architecture and indeed anything is accurately calculable by Fresnel and Lambert and all lighting software uses these ideas. Taking a mobile phone, for example, we see a reflection of our world off of the front glass, then the aerial systems that transmit the data use Fresnel Zones to maximise the signal strength. After that the entire internet is connected by fibre-optics whose total internal reflection allowing extremely long runs of cables, are fully understated by his work.
Lastly, some aspect of the Rosetta Stone, in the British Museum, tells us something about Fresnel’s character. As described, in Andrew Robinson’s excellent biography of the polymath Thomas Young, “The Last Man who knew Everything” (1) describes how Young was the first to be able to translate Hieroglyphics into Demonic and Greek. He looked at the elliptical borders around certain hieroglyphs (cartouches) and concluded that these were the names including Ptolomy for example. From this, the beginnings of translation were born and this directly allowed Champollion to run with the idea and improved translation further still. However, he never admitted any help from Young and this soured their relationship. But with Fresnel, although his correspondence with Young was not always in agreement, their correspondence was fruitful and indeed Young’s recommendation directly lead to Fresnel being awarded The Rumford Medal, which was brought to him on his death bed soon before his premature death in 1827. He had TB disease and was just 39. When pondering whether we are to survive living on our planet, I feel that as well the technology of the internet, Fresnel’s attitude: of people from other countries, who don’t always agree but correspond for the greater good of mankind, is timeless.
Peter Phillipson is the Senior Lighting Designer and Principal of Future Group Lighting Design. He is a Member of the Society of Light and Lighting and has chaired their London
Events Committee since 2011. Peter has been involved with the IYL 2015 and on December 2014, he lit the Downing Street Christmas tree, including the design and production of special IYL 2015 decorative baubles with Inessa Demidova. He is also currently involved with the off-grid lighting charity, Gravity Light.
Peter has worked with light for most of his life and from a very young age, sometimes holding multiple positions at any one time. He has worked in the theatre on many professional shows and ran a lighting laboratory designing optics as well as writing software. He worked as an animator for a 3D animation studio, and he has designed and run architectural lighting projects all over the world. Early in his career he won the Millar Award (forerunner of the Young Lighter of the Year) and on the strength of this was sponsored by the Thorn Lighting to go to university. He has worked at DHA designing lighting for architectural effects and for museums.