Numerous visual artists have declared the central role of light in their art, and the source of that light plays a vital role in the composition of landscape paintings. As all but nocturnes rely on natural light from the sun to create the image, that light determines the overall look of the painting.

For a landscape artist painting from a view in front of them, there’s limited choice as to what is possible. In the northern hemisphere, if the landscape to be painted is to the north of the point of view, that view will be well-lit; if it’s to the south it will be in shade. There is some flexibility, of course, according to the time of day, but that also affects the elevation of the sun, which in turn determines the colour-balance of its light and various transient effects.

Lighting also determines one of the most difficult aspects of landscape painting: cast shadows. In natural vision, these give the viewer important clues to depth and the three-dimensional structure of a view. Moreover, all these lighting effects are major contributors to the look of the painting.

If painting in front of the motif appears difficult in terms of getting the lighting right, it’s even more of a challenge when composing idealised landscapes from sketches and memory, which are often obtained under quite different lighting conditions. Bringing a realistic look to a view which never existed is far harder than it might look.

This is one of Nicolas Poussin’s great skills, for which he must have been able to visualise in his mind his idealised landscapes in near-perfect detail. In his Landscape with a Calm from about 1651, the sun is to the left of and behind the viewer, providing a crossed light which has remained popular in most landscapes, as it produces marked contrasts between lit surfaces and those in cast shadow.

The observant landscape painter also knows how the light affects clouds, which appear brilliant white where they are in full light, and dark grey when in shade or the shadows cast by other clouds. Because of the complexity of skies, the wise artist draws on a library of careful ‘skying’ studies.

Poussin’s choice of lighting makes this a brilliant painting, but demands meticulous detail in determining which surfaces are shown lit, as with the façade of this palatial Italianate mansion, and which are seen in shade or cast shadow. This also has to be consistent with the lighting shown on the sheep, and in the distance. That’s a painstaking task only suitable for the studio, of course.

While Claude Lorrain also painted landscapes in crossed light, his most characteristic were into the sun (contre-jour), with the sun low in the sky towards dusk.

Claude’s Embarkation of St Paula is typical with its towering classical buildings giving it great depth and drawing the eye from its foreground figures to the low sun.

Viewers, particularly those who don’t themselves paint, aren’t always good at noticing cast shadows in paintings. We are so used to seeing the world in relatively flat, even illumination that an absence of shadows doesn’t normally cause alarm. But when they are included, cast shadows make a great difference, particularly in views dominated by buidings, as shown in Gerrit Adriaensz Berckheyde’s Groote Market in Haarlem, Amsterdam of 1673. This is another example of the effects of crossed light, with the sun to the left of the viewer.

While the masters of the Dutch Golden Age paid attention to details like cast shadows, later painters like John Constable usually got away with rather vaguer indications of shadows. His finished version of The Hay Wain from 1821 looks meticulously detailed, but its shadows are of varying accuracy. According to those cast on the wall of the millhouse at the left, the sun is high on the right, providing crossed light to the whole view. But trees further in the distance at the right have vaguer areas of darkness underneath them, and the back of the standing figure in the centre is bright white.

JMW Turner was a great admirer of Claude Lorrain, and in 1817 painted his Claudean Decline of the Carthaginian Empire looking straight into the setting sun.

Many of his other paintings are also contre-jour, such as this view of The Harbour of Dieppe from about 1826. Turner’s landscapes were firmly rooted in the many sketches he made in front of the motif, but he faced similar challenges to those of Poussin in painting finished works such as this much later, and in the studio.

With the growing popularity of painting en plein air, landscape artists faced a different challenge. While there is every opportunity to capture a specific and very real state of light, that state isn’t constant, and in the time that a careful oil sketch is made, the sun has both moved and changed in elevation.

The most exceptional painters, Camille Corot and Camille Pissarro, trained themselves to capture cast shadows at a single moment, and their remarkable paintings are fine examples of the value of doing so. Pissarro’s Hoar Frost at Ennery from 1873 is one of the best, with its sun being low and behind the right of the viewer. This results in the rhythmic shadows of unseen trees being cast on the field. He also makes overt use of colour in those cast shadows, one of the controversies raised by the Impressionists.

Paul Cézanne’s early Impressionist landscapes are a complete contrast. Whether he was unable to develop Pissarro’s technique for freezing light and shadow, or simply had no interest in trying to do so, is unknown. When he painted The House of Père Lacroix, Auvers-sur-Oise alongside Pissarro’s easel in 1873, different passages of his painting show different cast shadows, revealing how sections of the roof were painted several hours apart.

As shown in the marked-up image below, the angle subtended by the shadows isn’t consistent. In some, the sun is high in the sky, close to its zenith, but in others rather lower. These imply a wide range of solar elevations, an issue which often affects those still learning how to paint plein air.

While other aspects of composition underwent radical change during the late nineteenth century, light and its effects remained a more stable feature, and continued to pose problems for many masters.

Another who had a struggle with cast shadows is Georges Seurat, in his famous Sunday Afternoon on the Island of La Grande Jatte from 1884-6, whose painstaking deliberation is the antithesis of the plein air view. During the hundreds of hours which Seurat spent applying small marks of paint to construct this monumental work of Divisionism, his lighting conditions wandered.

The woman standing fishing at the far left of the painting casts her shadow at an approximate angle (viewed from above) of 0130-0200 by the clock face, and hers is a long shadow too. Follow her shadow back until you meet a man standing wearing a ‘pith’ helmet, and he casts almost no shadow, as if the sun was almost vertically above him.

Continue to the right and towards the foreground and there is a woman holding a red parasol, walking towards the viewer, with a small girl beside her. Their shadows are cast in a different direction, closer to 0230-0300. Although most of the figures beyond the immediate, shaded foreground are seen to cast their own shadows, there are almost no corresponding shadows cast by the trees closer to the water, leaving most of the grassy area in unbroken sunlight.

Light is fundamental to paintings, and its challenges remain today.