252. The ideal of artificial illumination is to have the light coming from overhead, and to have it so thoroughly diffused that no object in the room shall appear conspicuously brighter than any other.

While it is impracticable to attain this ideal, with the means at hand at the present time, yet it should be so kept always in mind that mistakes in lighting may be avoided.

Lights of great brilliancy, such as electric arc lights, not only dazzle the eye, but frequently produce blindness. Oculists strongly condemn them, because they impair the vision of persons using them. The trouble is due mainly to the brilliancy of the light.

In using artificial lights for illumination, the aim should be to illumine all objects within the ordinary field of vision to about the same degree of brilliancy as that afforded by diffused daylight. Objects which are lit up by direct sunlight are usually too bright to look at continuously.

The flames of gas burners or lamps are much too bright to be looked at directly, therefore they should be screened so that whatever light reaches the eye shall be reduced to a moderate intensity.

The physiological effect of a light which shines in the eyes of a person who is looking at something else, is to produce considerable nervous irritation and fatigue, if long continued. Thus, if a gas burner or kerosene lamp, or any bright object, comes within the ordinary field of vision while a person is listening to an address, and is looking towards the speaker, it will cause a great deal of uneasiness. A few lights misplaced in that way will fatigue an audience to a greater degree than is generally supposed. Therefore, all lights which are located in the vicinity of a person addressing an audience, either above or behind, or at either side, should be fully covered by opaque screens which will prevent any light from passing towards the audience.

While the irritating brilliancy of such lights may be mitigated by means of globes of white or opal glass, yet they continue to be conspicuously bright, and are very objectionable. The best result is obtained by using opaque screens which reflect the light back upon the platform.

For similar reasons all chandeliers or pendants should be hung so high that the lights will not come within the field of vision of any person looking towards the platform or speaker.

253. Large audience rooms, such as churches and lecture rooms, can be illuminated to best advantage by means of groups of small burners which are located near the ceiling, and are provided with proper reflectors to project the light downwards. These sun lights may be arranged in a great many ways, and can be adapted for almost any kind of service. The light which they give is more agreeable than that from a single burner of equal power, because it proceeds from a large number of flames, and is thus so diffused that the shadows are very soft or indistinct.

This method of lighting is correct in principle, and it should be employed for domestic lighting to a much greater extent than it is at present. While there are some difficulties in carrying out the plan on a small scale, yet these should act as a stimulus to invention rather than as a bar to improvement. The introduction of the modern high-power lamps, such as the Wenham regenerative and the Welsbach incandescent, makes it very necessary that great improvements be made in the modes of distributing and diffusing light. There is a great need of such improvements in domestic illumination.

Flat gas flames, when turned horizontally, give a brighter illumination to objects below them than when burning in the ordinary erect position. The gas flames in overhead sun lights should always be horizontal.