It is an interesting fact that on a perfectly overcast day no object on the earth's surface can be brighter than the sky unless it be self luminous. On cloudless days a white object may be as much as 10 times brighter than the sky although usually it is about six times brighter. Incidentally the clear noon sun is many million times brighter than the shadows in a landscape.
It is difficult to discuss the artistic aspect of light and shade in nature because this involves taste which, in general, is more or less inde terminate. However a few points will be brought forth because they appear so definitely established after years of observation. Variety is perhaps the keynote of nature's beauty. Take a scene which may appear commonplace at mid day on a clear day and it is not uncommon for it to be enchanting in the early morning or late afternoon. A study of this scene ap pears to indicate definitely that the beauty near the ends of the day is due to the long shadows and hence a greater variety in light and shade. A clear sky may hepleasing in its tranquillity, but to be beautiful or powerfully effective variety is necessary and this is obtained by cloud effects. Great areas of uniform bright ness such as an overcast sky conspire with the absence of defined• shadows to produce an effect toward which we are indifferent and often dis pleased.
It is interesting to note that the sharply defined shadows outdoors on a clear day are not annoying and are even very pleasing yet shadows of a similar sharp contour are usually displeasing indoors under artificial lighting. The difference may be accounted for by the much greater luminosity of the shadows out doors and the adaptation of the eye to a much higher level of illumination intensity so that the contrasts are less violent. These points might well be borne in mind in the practice of artificial lighting. A symmetrical distribution of light in interiors produces effects which ap proach the light and shade of nature and the finer sensibilities recognize that there is mach to be gained in departing from the common symmetrical distribution of light in artificial lighting systems.
It is seen that light and shade is of great importance in many activities, both from the scientific and artistic viewpoints. It is the most important .factor in vision because every
one is more conscious of form than of color; however 'color plays a part in vision even though unconsciously. For example, in provid ing an illumination for a certain activity it is well to study how the perception of .the ob jects is best accomplished. It may be that cer tain small objects may be best seen outlined in shadow against a bright background or vice versa. If they have polished surfaces, the regularly reflected high-lights may be of the greatest importance. Thus it is seen that the background is a large factor in the discrimina tion of objects.
The shadow is an important factor in model ling an object and the cast shadow likewise lends its aid. Under the illumination of an overcast sky or an indirect lighting system, ob jects are less distinctly visible because in these cases only the profile or silhouette is the dominant factor. Under such conditions of illumination much of the advantage of the modulation from light to shadow and of the form of the cast ,shadow is absent. Although somewhat disadvantageous in the perception and recognition of fine detail, such types of light-distribution are exceedingly applicable to some classes of problems. Perhaps no system of lighting has been as successful as the so called indirect lighting in producing light and shade effects befitting the spirit or mood of an interior. An excellent field for such observa tions is in churches because so many types of architediure are available and the different creeds call for different expressions of the interior. This is not commonly recognized but it is nevertheless true and the possibilities of lighting in this respect have been recognized to some extent even though subconsciously.
Without taking the space to summarize this article, which in itself is a brief summary of an extensive subject, it may be repeated that light and shade must be ranked as one of the most important factors in human existence because it is.the most essential factor in vision. It is a many-sided subject, embodying the scientific aspect of the appearance and hence of the discrimination of objects, the asthetic aspect of many scenes, the psychology of light, the aims and limitations of the imitative arts and many other aspects. See ART DRAWING.