Lighting Practice Outside the Home

Schools and Meeting Places.

Long continued close visual application indoors, particularly among young people, has come about in relatively recent times, and the practice of artificial lighting installations has not kept pace with the knowledge of what constitutes proper conditions for the conservation of eye sight. A comprehensive survey in 1932 reported 22% of grade school children with defective vision while in the colleges this percentage rose to 4o. The adolescent eye needs better light for the same task and the effects of glare from bare or bright sources, or the twilight zone strains of inadequate intensities, not only have been found to induce ocular deficiencies of a permanent nature but also may increase the cost of education.

When more than 90% of human knowledge is obtained through vision one can appreciate the vital importance of good school lighting. Many a "backward" child has simply suffered from poor lighting and faulty eyesight. When the pupil comes from perhaps 500o foot-candles of daylight outdoors into often less than 5 f oot candles of desk-top illumination he must adjust to a severe de ficiency. Often the blackboard lighting is even less. The normal grade schoolroom should have not less than Io foot-candles aver age, and preferably double that figure. The equipment commonly installed between 1915 and 1935 consists of four or six diffusing glass globes surrounding 15o or 200 watt lamp bulbs. More

recently the best practice calls for an increased size of glass globe to hold the surface brightness below 3 candles per square inch, increasing the height to 10 feet or more above the floor, and employing no less than a 200 watt lamp in a 16 inch diameter globe, or a 30o watt lamp in an 18 inch globe. Ceiling surfaces should have a reflection factor of 8o% or more and the upper walls approximately 5o%.

For sewing and drafting rooms the values should exceed is foot candles and for auditoriums and assembly rooms, not used for study purposes, some 3 to 5 foot-candles suffice. The indirect or semi-indirect systems have grown in favour, supplemented by prismatic plates or lenses directing a fan of light against black boards or on fixed work-benches. The use of the photo-electric cell for the automatic control of the artificial lighting in place of the manually operated wall switch, insures a more constant illumination at all times. A very prevalent fault has been to suspend lighting fixtures too low within the fields of view and to provide insufficient wiring capacity for adequate wattage without severe losses. An installation capacity on the order of 5 watts per square foot is present good practice. Further data on the standards of school lighting are obtainable from the American Standard Codes issued by the Illuminating Engineering Society and the American Institute of Architects. (S. G. H.)