Environmental Engineering Reference
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Fig. 5.5 Normalized spectrum of typical (4,000 K) fluorescent lamp
very closely matched to the spectral characteristics of a source (e.g., the sun), the
performance of the resulting system would reasonably be expected to exceed
that of a system in which the two were mismatched. The significance of this
reasoning becomes important when we consider the spectrum of an average
(4,000 K, T8) fluorescent bulb, shown in Fig. 5.5.
Clearly the fluorescent spectrum that is shown differs significantly from the
visible portion of the solar spectrum. Thus the wavelength distribution is not
optimized for human vision. From a systems point of view, one could reason-
ably speculate that visual acuity for tasks such as reading would be poorer
under the fluorescent spectrum in Fig. 5.5, compared to the visual acuity one
would experience when performing the same tasks under the same quantity of
light with the solar spectrum shown in Fig. 5.3. Reduced visual acuity is a source
of discomfort and diminished visual performance that also leads to decreased
feelings of well-being. Anyone who has experienced a decline in visual acuity
due to age or other factors can attest to the malaise it creates. By extension, we
can reason that if visual acuity is increased under natural lighting, improve-
ments in one's feeling of well-being and improvements in one's performance on
tasks requiring visual acuity (reading, writing, and detailed physical work)
might also be increased.
Beyond visual acuity issues, it is generally appreciated that organisms
respond differently, at an organic level, to optical stimulation from different
portions of the spectrum. Certainly the UV spectrum has its organic benefits
(vitamin D production and prevention of rickets) and hazards (sunburn and
carcinoma). In addition, the use of fiber optic blankets that emit blue-green
light have become common in the treatment of infants with elevated bilirubin
levels. These are limited examples of organic spectral affects that are generally
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