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FOURTH SESSION

President Williams called the meeting to order at eight o'clock Wednesday evening, announcing as the first order of business the paper by Mr. E. A. Norman, of New York, entitled Efficiency of Various Methods of Illumination.

The following paper was presented by Mr. Norman:

EFFICIENCY OF VARIOUS METHODS
OF ILLUMINATION

The study of illumination is very complex, insomuch that no general rule can be laid down to govern different situations. Each installation must be studied separately; the color of the wails, ceilings and floors, style of illuminant, method of installation, and effect desired, must all receive careful attention.

Several situations may present themselves to the illuminating engineer. First, the customer who desires the most light at the smallest possible cost, without regard to artistic effect. Second, the customer who seeks entirely the artistic. Third, the customer who has a desire for the artistic, as well as a desire for economy developed to a great extent. The last is by far the most common and the most difficult to satisfy. The illuminating engineer must study each one of these cases very carefully, determining upon the form of illumination to be used and the method of its installation.

In New York city we have illustrations of practically every form of illumination. Incandescent lamps of different types, enclosed-arc lamps, diffuser-arc lamps, flaming-arc lamps, Nernst lamps, mercury-vapor tubes, Moore tubes, and so forth. I think all of these types are at present in use in our post-office, presenting an appearance at night that can be better imagined than described.

From an aesthetic standpoint, with the possible exception of ball-rooms, assembly-halls, and so forth, a room lighted with uniform intensity is not desirable. It is not necessary to illuminate every niche and corner-shadow must exist to display form, to relieve monotony, and to give depth. It is not alone sufficient to know the area of a room to prescribe a certain illuminant. The decorations must be carefully considered. A wall of one color will absorb more and consequently reflect less light than will a wall of another color. In addition to this, the color scheme of the room must be considered; lights of different colors will change the color values of the decorations.

The appended table, taken from The Upholsterer, shows color changes effected by different color rays:

Orange rays falling on white make it appear orange

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When the style of illuminant has been decided upon, the question as to the manner of its installation arises. Shall the illumination be direct or indirect, and what style of direct or indirect shall be used?

The chief objection to direct lighting is due to the glare. This may be removed to a certain extent, however, by the judicious use of reflectors and shades. Some form of shade is almost a necessity with the high-candle-power units in so general use at the present day.

Indirect lighting is undoubtedly attractive, but where used alone soon becomes tiresome. The same uniform intensity is fatiguing to the eye. The absence of an apparent source, together with the total absence of shadow, produces an unnatural . effect.

A combination of direct and indirect methods would undoubtedly be productive of excellent results, tending to remove the objections that arise from the use of either system alone.

In a paper presented before the Illuminating Engineering Society, I pointed out that by means of concealed lighting the glare of the direct lighting would be reduced. This is well shown in Figures 1 and 2 illustrating our Twenty-seventh street auditorium. Figure 1 shows the ceiling lighting alone, Figure 2 the entire lighting, ceiling, cove and side brackets. The glare or halation so noticeable in the first illustration is missing in the second.

Arc Lighting

The question as to what style or make arc lamp to install must be decided by its intended use and its environment. In one installation it was desired to replace incandescent lamps (Figure 3) by arc lamps in the riding ring of a certain riding and driving club; 16 diffuser-arc lamps were installed, and proved undesirable; neither the color nor the volume of light was satisfactory. Six flaming-arc lamps were then installed, flooding the ring with a warm, brilliant light. The dark tanbark and dark walls absorbed most of the white light, but reflected the yellow.

On the other hand, one hotel complained that in the room. where silver was cleaned, illuminated by means of incandescent lamps, the results were unsatisfactory. The silver, apparently clean under the incandescent light, when brought into daylight would appear tarnished. Owing to the low ceiling, it was impossible to install an ordinary arc lamp, so Liliput arc lamps (Figure 4) were hung, and thus far have given perfect satisfaction. The white light in this case was desirable. These cases are cited simply to show that the surroundings and the result desired must always be considered carefully. In an ice-skating rink, for instance, a much better effect would be produced by

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