A company's productivity depends on the capacity of individual employees to work effectively. Properly designed lighting systems can and do produce measurable, long term improvements in performance, morale, reduced errors, reduced absenteeism, and higher quality products and service.

Visual comfort and productivity are directly related. This shouldn't be too surprising: The higher a workers visual comfort, the higher the productivity.

What do we mean by visual comfort and how can we measure it? Visual comfort is how easily we can view tasks. More often visual comfort is discussed in the negative terms of discomfort glare, disability glare and veiling reflections. High levels of these three conditions result is visual discomfort and lower productivity.

Discomfort Glare is the annoyance or pain caused by high luminances in a worker's field of view. The degree of discomfort glare depends on the size, luminance and number and position of glare sources. Background luminance is also a factor. The most common causes are windows and luminaires.

Interestingly, increasing background luminances decreases discomfort glare. The Visual Comfort Probability , or VCP, of a lighting system is a rating that indicates the percentage of people that will find a given discomfort glare acceptable. The VCP rating is applicable direct lighting fixtures with the viewer in a specific location and looking in a particular direction. A VCP rating of 70% is usually considered acceptable, but 80% is required for areas with computer monitors. VCP differences between fixtures of 5 or less are not significant.

Disability Glare results from light scattering within the eye, which, in turn, decreases contrast and reduces visibility. This condition is also called veiling luminance. The most common example is the glare on glossy magazine pages that makes it difficult, if not impossible to read. Disability glare can occur with or without discomfort glare and / or veiling reflections.

Veiling Reflection is the reflection of a large luminance area on a task. This results in a loss of contrast between the task and the background. Veiling reflections are usually caused by windows or luminaires placed above or in front of the task.

A measure developed for veiling reflection is called Equivalent Sphere Illuminance , ESI. The footcandles of ESI indicate how much illumination must be provided for a task in a theoretical perfectly diffusing hemisphere to provide the same visual performance as the actual lighting system. The higher the ESI, the better.

The color rendition of a lighting system also affects visual comfort. Our sense of well being is influenced by the accuracy of an object's colors.

In addition to visual comfort, the four factors of seeing: size, contrast, brightness and time also affect productivity. When each of these factors is high, visual performance is high.

Relative visual performance, RVP, is the percentage likelihood that an individual can perform a particular task of a given size for the lighting system in question. Both contrast and background luminance are taken into consideration.

This graph shows that the RVP varies with the contrast or background luminance. Below a certain threshold, performance decreases significantly. Designers should be designing lighting systems with RVP ratings illustrated.

Today's workplace incorporates ergonomic furniture, computers, sophisticated telephone systems, faxes, calculators and photocopiers, among other tools. As important as these tools are, it is lighting that really affects how people work.