Because of the stimulating effect of sunshine, may not an excess of sunshine be just as detrimental as a deficiency? It has, indeed, been assumed that the climatic dangers of the tropics are largely due to the injurious tropical sunlight, particularly to the abundance of the ultra-violet rays. Woodruff holds that the failure of the white race to colonize in the tropics is due to the excessive light, and not to the heat and humidity. The light, he contends, tends to produce ennui, neurasthenia and ultimate collapse in blond persons (26). This conclusion is not sustained by recent investigations. Experiments have shown that monkeys do not succumb from insolation in the tropical sun if care is taken not to allow the bodily temperature to rise, by conducting away by brisk air currents the excessive heat (Aron, 23). The injurious quality of the solar light is thus due to the infra-red and not the ultra-violet rays. The white man can secure adequate protection in the shade from the heat rays, and by wearing white clothing he can be adequately protected from the ultra-violet rays. Whether the retinal excitation by the sun’s rays exerts any stimulating influence is not known. It is known, however, that red colors are stimulating. They excite some animals (for example, cattle, frogs and turkeys) and increase muscular strength. Thus Fere obtained the following strength records: with ordinary light, 23 units; with blue, 24; with green, 28; with yellow, 30; and with red, 42 (29). Colors, as is well known, possess marked affective qualities, due not merely to the affective tone of the sensation and the sense feeling, but to the affective elements of consciousness, namely associations, emotions and sentiments (29). That sunlight does exert psychic influences apart from any specific retinal influence is a matter of common experience. Nevertheless, the most important visual influence of sunshine is perhaps not the emotional satisfaction, cheer or exuberance which it engenders, but the optical value of good daylight. Daylight is relatively colorless because it contains both chromatic and achromatic light. A bright colorless illumination is best from the standpoint of visual efficiency, health and affective quality. It is less fatiguing than a colored light or than intense or dull artificial light. Electric lights are often too intense because of the proximity of the light or because the rays are thrown directly into the eyes or directly upon the object under observation. They thus over-stimulate the sensitive layers of the retina, and this may cause degenerative changes. Mercury vapor lamps and old Welsbach burners emit a greenish flame whose affective quality is very disagreeable to many persons. Many of the gas jets in common use, unless equipped with incandescent burners, not only give a weak flickering, dirty yellowish light, which is extremely fatiguing and irritating to the eyes, but they also vitiate the air of the living