Bright Lighting in Display Areas Can Brighten Your Profit Picture

Schools or offices using daylight from a side window wall as primary source of light, and artificial lighting as a supplement, have more effective illumination than buildings with overhead lighting only, a university study reveals.

In fact, about one-half as much illumination is needed if daylight walls are used as the primary source. Most ordinary reading and writing tasks require twice as much illumination if it comes only from overhead sources rather than sidewall lighting.

These are conclusions drawn from a research project which analyzes the effect on visual performance of direct lighting from a side window wall. The effect of reflected glare was studied by Professor J. W. Griffith, internationally known daylight authority at Southern Methodist Univereity. Professor Griffith has been associated with Libbey-Owens-Ford Glass Company for 15 years in studies of daylighting.

Professor Griffith researched the quality of light from a side window wall and from overhead sources on visual tasks. He studied the efiectiveness of each type of lighting on tasks, rather than merely how much light each system produces on a given task.

He measured the contrasts of tasks utilizing pencil, ink and ballpoint pen, as well as tasks involving typed material and print. Simulated daylight tests were made on illumination from an overcast sky and uniformly bright sky, as well as light emitted when venetian blinds were drawn halfway. He also tested overhead lighting from a luminous ceiling and from fluorescent luminaires.

The tests showed a considerable loss of contrast from reflected glare on tasks Iighted only by overhead systems as compared to tasks illuminated only by a side window wall.

Four basic factors in seeing, Professor Griffith notes, are (1) time, (2) size, (3) brightness and (4) conrrast. Seeing is made more difficult by reducing any one of these factors. To maintain equal visibility any loss of vision must be made up by changing one or more of the other factors. But the professor's research showed additional illumination cannot be obtained by increasing the brightness of the luminaires without increasing the loss of contrast at the task.

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