Environmental Engineering Reference
In-Depth Information
custom mixing rod to adapt the light to the hexagonal shape. Sunlight Direct
had also continued to work on the molding technology for the primary mirror,
and the mirror quality was approaching that of the glass mirror that had been
used in the initial prototypes.
With the design of the system reaching maturity, detailed spectral character-
ization of the optical system was conducted to evaluate the efficacy of the
different components and their impact on the overall performance of the system
[15]. The spectral characterization of the system showed that the natural light
from the HSL luminaires (measured with the electric lights extinguished) dif-
fered only slightly from the solar spectrum, with a small loss in the red portion
of the spectrum (Fig. 5.17).
At the time of this writing, more than 20 HSL systems are installed at
various locations throughout theUnitedStateswith tenof those organizations
participating in the detailed beta test program [5]. Figure 5.18 shows an
installation in progress at ORNL with four units on a newly constructed
building, and Fig. 5.19 shows various views of an installation at the Walmart
in McKinney, TX.
The energy performance at the beta test sites is monitored to accumulate
energy savings data. The plot in Fig. 5.20 shows the impact of the HSL system
on the energy used for lighting in a typical office environment. These data,
fromSan Diego State University, represent the energy used to provide lighting
in an office area at the university. The data show the onset of energy usage,
when the lights are turned on early in the morning. The full electrical load of
1.00
Sunlight
Fiber Output
0.75
0.50
0.25
0.00
350
400
450
500
550
600
650
700
750
wavelength (nm)
Fig. 5.17 Normalized comparison of direct sunlight and light from HSL fibers
