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When facilities managers or employers receive a request for full-spectrum fluorescent lighting, the person receiving the request cannot be blamed for not knowing how to respond. Lighting design should accommodate six human needs: visibility, activity, health & safety, mood & comfort, social contact & communication, aesthetic appreciation. Claims about the superiority of one lighting product over another should be evaluated against criteria in these areas. Evaluating the complete lighting design requires attention also to architectural design, maintenance, economics, and energy issues. No one product fits all circumstances.
Evaluating Full-spectrum lighting
A full-spectrum fluorescent lamp is one that is designed to mimic daylight in the north sky, having emissions in all parts of the visual spectrum and some emissions in the ultra-violet range. A full-spectrum fluorescent lamp appears slightly blue, and renders colours well. Some people claim that the similarity of the light from a full-spectrum fluorescent lamp to daylight makes this inherently better for meeting human needs, by improving visual acuity, mood, and school achievement and attendance. The National Research Council's Institute for Research in Construction has reviewed the literature on full-spectrum lighting to clarify the validity of this idea. Most of the claimed benefits are not conclusively supported by the scientific evidence.
Visibility. Seeing task details depends on the size, contrast and brightness of the task and on characteristics of the viewer (age in particular). Some researchers theorise that lamps with relatively more blue light will improve visual acuity because this stimulation appears to reduce pupil size, which increases depth of field. If this were true, full-spectrum lamps would produce better visibility than most other lamp types. However, the effects that have been demonstrated in the laboratory under strict experimental controls have not generally been observed in field studies under normal viewing conditions.
Performance and behaviour. Several prominent studies involving classroom lighting received widespread publicity, and have led some classroom teachers to change the lighting in their classrooms (even at their own expense!). However, close examination of these studies revealed several problems in the research design and statistical analysis. The chief problem is that most studies have looked at different teachers in different classrooms with different lighting. Differences in achievement, attendance, or classroom behaviour could have been caused by differences in socio-economic circumstances, parent behaviour, and teaching style, among other variables.
Mood and comfort. Probably the most common claim for full-spectrum fluorescent lighting is that it prevents or treats depression. It is true that light therapy is an effective treatment for the clinical condition Seasonal Affective Disorder (SAD), and it might even be helpful for other forms of depression, but the type of white light that is used in light therapy does not affect treatment outcomes. Any very bright white light, administered at the right time of day, is effective. Furthermore, the effectiveness of this medical treatment doesn't mean that everyone should be exposed to high light levels all the time.
Safety and health. Other health effects ascribed to full-spectrum fluorescent light are based upon its ultraviolet component. The literature is confusing on this point. One group suggests that the presence of ultraviolet light in interiors is essential to health because modern, Western society receives too little exposure to naturally-occurring UV light for health. Others fear than UV exposure from fluorescent light (full-spectrum light in particular) could be a carcinogen. The total UV dose that one would expect from the lighting sources in a typical office, however, is very small in comparison to that received outdoors, even at relatively northerly latitudes.
Aesthetics. Full-spectrum light does make it easier to distinguish between colours than some other lamp types. However, it is not the only lamp type that provides good colour rendering, and other lamp types will be more appropriate for some places. Few of us would want the very cold colour of a full-spectrum lamp in our living rooms; we would rather have the warm colour of an incandescent lamp.
Social connections and communication. Non-visual processes related to lighting also influence us. Being in environmental conditions, including lighting, that we prefer puts us in a good mood (what psychologists call positive affect), which leads us to behave more co-operatively and creatively. Preferences for different types of light vary, but some studies have found that full-spectrum lighting is not well-liked in comparison to warmer colour temperatures, especially if the light level is low.
CONCLUSIONS: IS FULL-SPECTRUM LIGHT THE QUALITY CHOICE?
Most of what we need to know about lighting types and their effects on people remains to be learned. For example, there might be some benefit to using lamps with some UV output in circumstances where there is very little daylight (such as the far North), but no one has studied this question.
We do know, however, that for general use in offices, schools, and institutions, there is no particular benefit to using a full-spectrum lamp over any other lamp type. If one wants to make fine colour discriminations, then one needs a lamp with good colour-rendering properties, which could be a full-spectrum lamp (but need not be).
The most important consideration in creating good-quality lighting is not the lamp type. Codes and standards are silent about lamp type, focusing instead on light levels, distribution, and glare control as the most important considerations. Characteristics of the end-users, the setting and activities in it, the architecture, and economic issues all come into this complex equation.
© National Research Council Canada, 2000
IRC performs research on the building envelope, fire risk management, urban infrastructure and the indoor environment. IRC also provides a construction product evaluation service and assists in the development of the national building codes. For more information about indoor environment research at IRC, including lighting, visit http://www.nrc.ca/irc/ie.