An examination made in 1924 and 1925 of a vast amount of medical literature brought out some interesting facts with respect to light. A preponderance of medical testimony with respect to the value of light establishes the following: that sunlight is one of the most effective bactericidal agents known; that sunlight carefully administered will not only cure rickets and surgical tuberculosis, but will prevent their occurrence; that sunlight is a great stimulus to health, causing chemical changes in the skin and blood and increasing cheerfulness; that the heat of the sun rather than its light is responsible for most of the ill effects noted from over exposure; that all sunlight acts as a tonic; that ordinary window glass filters out or excludes most of the beneficial short ultra-violet rays; but that the lower ranges of ultra-violet will pass through ordinary window glass and kill bacteria if sufficient exposure is given.
Some negative evidence with respect to the value of sunlight was discovered, but the great preponderance of medical testimony is on the side of its positive value.
Ventilation was studied to some extent, but the report of the New York State Commission on Ventilation was so conclusive that it was deemed unnecessary to go further. That report contains several statements of significance to this discussion. The first is, that early sanitarians overemphasized the importance of pure air and the harmful effects of carbon dioxide; that foul air however does affect the appetite and the work output; that it is overheated air which is really deleterious; that good room ventilation requires a temperature of 68 degrees, or less, without the production of chilling drafts.
Some examination was made as to the restful effects of grass, trees and shrubbery.
The best report on the relation of public morals to overcrowding was written by one of the justices of the municipal court of the city of New York, and published in full in a report of the State Commission on Housing and Regional Planning. This showed a direct relationship between public morals and room overcrowding - a fact which is not news. It also showed a relationship between room overcrowding and land overcrowding, which is directly related to the problem of zoning.
The results of an examination of the number of cases of reportable infectious diseases by weeks in the city of New York over a period of eight years compared with the reported sunshine and recorded temperature in the city of New York during the same period indicates similar interesting correlations. The total number of reportable infectious diseases rises rapidly at the beginning of each year to a high point in February; and then usually falls off, reaching a low point about September 1st, and rising again in the autumn.
The amount of sunlight available is directly the reverse - low in January, rising to a high point in June and July and beginning to fall off in the autumn. As a matter of fact, there is a lag of about 30 to 45 days between the high point of sunlight and the lowest point in the disease curve, and a similar lag between the lowest point in the sunshine curve and the highest point in the morbidity curve.
The entire field was thus canvassed to determine what, if any, relationship exists between density of occupancy and health and welfare and zoning.
Out of all this mass of material, one fact stands out clearly, the value of light and of sunlight in particular.
How to get this valuable gift of Nature into our buildings is the question. Records of the Weather Bureau show that the United States is fortunate in the amount of sunlight available. In New York City over a period of 50 years, the sun shone 59 per cent of the time when it would have been possible for it to have cast a shadow. In Philadelphia the figure was 57 per cent of the time. Just east of New York, on Long Island, we have in the New York Region the high point of sunshine on the Atlantic Coast - 78 per cent of possible sunshine, exceeded only by the area in the southwestern part of the United States, near Flagstaff, Arizona, and El Paso, Texas.
Detailed astronomical calculations were made to determine the length of shadow cast by buildings of various kinds, and the area of the sunlight upon the floor of the room through a given window of standard size for each 30-minute interval throughout the day.....These studies show that it is possible to guarantee one-half hour of noon sunlight, or its equivalent in sunlight intensity, morning and afternoon, in every room of every dwelling 25 feet square, without using more land than is customary in our usual subdivisions with lots 40 feet by 100.