Hoffman, D. L.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  The Student's Lamp Creators:  Hoffman, D. L. Issue Date:  Mar-1920 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 3, no. 2 (March 1920), 13-14. URI:  http://hdl.handle.net/1811/34040  Appears in Collections: Ohio State Engineer: Volume 3, no. 2 (March, 1920)         The Ohio State Engineer 13The Student s LampBy D. L. HOFFMAN, E. E. '20A story recently appeared in one of our popularmagazines of a minister who made a great discovery.Some of the men in his congregation went to sleep inspite of his best efforts at oratory. The women folksstayed awake. The reverend gentleman searched fora reason for the phenomenon. A little science wasbrought to bear and the conclusion was that the menwere lulled into slumber by a glow of light that hadbeen located above the pulpit. The results of a quietinvestigation brought out that the women's hatsshaded their eyes, while the bare-headed men werewholly unprotected. As the story goes, the misdi-rected light was eliminated and the masculine mem-bers of the congregation are now wakeful and inter-ested listeners to the minister's sermons.Without overdrawing conclusions, the above storycan be made applicable to may students who arehandicapped during study with misdirected light. Astudent made irritable by headaches from eye-strainproduced by a glaring light source during an eveningof study cannot start the next day in the properframe of mind to work at the highest efficiency. Im-proper illumination is expensive from any angle.Floor and table fixtures are being used more andmore extensively and the many styles and patterns onthe market indicate that practically all of themhave been designed from a decorative standpoint,with shades of metal, glass, silk, or a combination.As a rule unless specially designed this type furnisheslittle or no control of the light from the incandescentlamp. The shades must be dense, because the unit isalways in the field of vision. With dense glass ormetal reflecting surfaces the direct lighting reflectorthrows most of the light downward. Direct lightingreflectors distribute the illumination well, but oftenmay give glare and disagreeable shadows. With atable lamp the intensity of illumination on the tabletop is usually too high for comfort if the rest of theroom is to receive light from the same source. Atable or floor lamp can be designated to be effective bydirecting downward only enough light to give theproper intensity on the table top, and by directingthe remainder of the light to the ceiling where it willbe reflected about the room without discomfortingbrightness. There are floor and desk lamps on themarket which fill these requirements by a combina-tion of direct and indirect lighting. The direct lightis thrown downward and the lamps are shut out fromthe direct line of vision by dense shades; the indirectlight for the general illumination of the room is fur-nished by lamps in an indirect reflector at the top ofthe fixture. As a result the whole effect is very pleas-ing and the illumination is even and efficient. If acommon type of floor or table lamp is used, it shouldbe supplemented by general illumination produced byanother lamp, so placed that dark shadows about theroom are eliminated. In other words, the function ofthe local lamp should be merely to intensify the illu-mination at the work, or to give light in a particulardirection, as may be required.The eye sees brightness, but brightness is merelyvisual sensation. The sensation of brightness isaroused by a physical phenomenon, namely: the quan-tity of light emitted by or reflected from a luminoussurface. Arrangements of lighting that will intro-duce normal sensations, or sensations for which theeye is not adapted, are to be avoided. An opticallycorrect and visually efficient lighting arrangement ismore a matter of distribution of light than of itsquantity. It is not possible to lay down definite rulesfor lighting to cover all conditions. But certain fun-damental principles may be stated, which are foundin all good lighting. These are:Correct Intensity.Good Diffusion.Light from Proper Direction.Absence of Glare (both direct and reflected).In the normal process of seeing, the eye is calledupon to adjust itself for illumination intensities whichvary from several thousand foot-candles outdoors ona sunny day, to small fractions of a foot-candle in thesame location at night. At the very high values, ablinding effect from the large volume of light reflectedto the eye obliterates detail, while at the low rates, thequantity of light is so small as to render accurate dis-crimination impossible. Between these limits thereis a wide range of intensities at which good vision ispossible; consideration of economy naturally limitsthe intensities employed in artificial lighting to thelower values of this range. Light for the student, tobe correct, should be of such intensity that work canbe carried on without straining the eyes, and yet notbe of such high intrinsic brilliancy that the pupilof the eye contracts to such an extent that it cannotsee properly. Desirable light intensities for the classof work under consideration range from 8 to 12 foot-candles ; intensities up to 50 foot-candles would do noharm if proper diffusion is obtained. An illuminationof at least one foot-candle over the entire room shouldbe provided where desk or local fixtures are used. Inorder to provide sufficient intensity it is not necesarythat the largest lamp possible should be used; a lampThe Ohio State Engineerlarge enough to give the amount of illumination nec-essary for the desired effect is all that is required.The medium-sized lamp, frosted or opal bulb, is bestadapted for the study-room. For close work, such asreading, or writing, a high intensity of illuminationis necessary if eye strain and discomfort are to beavoided.By diffusion of light is meant the ability of the illu-minant to distribute light in all necessary directions,thus tending to produce an even illumination. Day-light on a cloudy day is perfectly diffused. The beamof a searchlight has no diffusion. Diffused light isdistinctly agreeable and easy to the eyes. It is acommon mistake in weak or overstrained eyes to re-duce the intensity rather than increasing the diffu-sion. ' ' Paper work'' calls for very little shadow sinceall the objects requiring distinctions are in one plane.The importance of light from the proper directionis obvious to all. One of the fundamental rules forproper lighting of study tables is to have the prepon-derance of light come from the left side.Among the most frequent and serious causes of badlighting are those due to glare in its various forms.Glare has been described as "light out of place."The most common cases of glare are those which aredue to unshaded or inadequately shaded lamps locatedwithin the field of vision. The bare local lamp is aconstant sourcme of glare which is extremely injuri-ous to the user's eyes. It is contended that the glarefrom even a small 15-watt lamp filament decreases theseeing efficiency of the eye 25 per cent. Glossy sur-faces of paper, desktops and woodwork are likely tobe sources of glare because of specular or mirror-likereflection of images of poorly designed light sources.This form of glare is particularly harmful because ofthe fact that the eye is often held to such surfaces forlong periods of time, and while the glare may not besufficiently annoying to be recognized as of a seriousnature, it may nevertheless in time produce eyefatigue or even permanent injury. Specular reflec-tion can frequently be prevented from striking theeye by locating the light source in such a positionwith respect to the work that specularly reflected lightwill be thrown away rather than towards the worker.The use of lighting units of large area, reducing thebrightness of the light source, moving the light out ofthe field of vision and using a good diffusing mediumglare, both direct and indirect, can be reduced to aminimum. Too much emphasis cannot be given to theharmful effects due to glare. The proposed industriallighting code of this state reads: Glare results indecreasing ability to see; it may cause temporary dis-comfort, and if the condition is long continued mayresult in permanent injury to the eyesight. The de-creased ability to see results in lower quality anddecreased quantity of output; consequently, asidefrom discomfort and danger to the eyes, glare is eco-nomically bad. Within the past few years an import-ant work has been undertaken by scientists in behalfof good lighting. Prominent among these is Dr. C. E.Ferree, of Philadelphia, a brother of Dr. Ferree ofthe University Faculty. He has made a series of teststo find out how light affected the human eye. Hefound that after three hours work under diffuseddaylight the eye lost practically nothing in efficiency,whereas, after the same length of time working with-in range of the rays of an exposed light the same eyedepreciated 86 per cent in seeing efficiency. Glarecan and does do more harm than any other part of apoorly designed system of lighting.The problem of student room lighting, from thestandpoint of utility, can be very simply stated. Fun-damentally it is to provide the best illumination forsustained vision of flat surfaces in horizontal or slight-ly oblique planes in which papers, pictures, and booksare usually examined.To summarize, the eyesight must be catered to bya uniform horizontal illumination, minus glare andobjectionable shadows. There should be no extremecontrast in the brightness of objects within the fieldof vision. The providing of light well diffused and ofample intensities will eliminate discomfort and theeye will not become excessively fatigued even withapplication for long periods of time. The severe re-quirements imposed on student's eyes by moderneducational methods create need for the best of work-ing conditions.

The Student's Lamp

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The Student's Lamp

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