In 2001, BPA replaced the art projection lamp as an energy project, replacing the PAR38 halogen lamp with a 15W and 23W compact fluorescent lamp (CFL). GATEWAY shows the optical performance of Cree PAR3812WLED lamps and two types of CFLs, such as light intensity, power, energy consumption and life. Although the CFL emits more light than the Cree PAR3812WLED, the LED light distribution is narrower, reducing the light intensity of the wall above the artwork and allowing the light to be concentrated on the artwork. And, compared to the 23WPAR38 and 15WR30CFL, the LED increases the vertical illumination contrast between the artwork and the wall.
The goals of the GATEWAY project include improving the visibility of the artwork in the hall, the lighting quality of the displayed work, and the appearance of the new LED replacement lamp. At the same time, BPA also pays attention to the energy consumption and cost saving potential of this new technology, and cooperates with Pacific Northwest National Laboratory (PNNL) to report and analyze the lighting performance before and after the retrofit of the luminaire.
First, the contrast between LED lights and CFL display
Table 1 compares the characteristics between CFLs and LED lamps. Two different models of CFL lamps are installed in different locations in the hall. Both fluorescent lamps have a divergence angle of more than 110°, while Cree LEDs have only 18°. The optical density of the center beam of the LED product is significantly higher than that of the fluorescent lamp. The fluorescent lamp is about 300, and the LED reaches 4465, which allows the LED lamp to concentrate more light in a local area.
The spectrum of the CFL is weaker in the long wavelength red range, which appears to be yellowish green compared to halogen or LED lamps. Cree LEDs offer better illumination quality and, like halogen incandescent lamps, have a high color rendering index. In terms of color rendering index, the display index of both CFLs is 82, and the two Cree LEDs reach 93, because Cree LED lamps will have more energy distribution in the long wavelength red spectrum region.
The three lamps are similar in power and efficacy, so the highlights of Cree LED applications are not energy saving and high brightness. In fact, the full lumen output of Cree LEDs is only a little more than half that of 23W compact fluorescent lamps. It has the advantage of being able to concentrate the beam in a small cone, which is especially suitable for local illumination. Cree LEDs emit less light in large angle areas.
When considering the application of local illumination to compare luminaires, the central beam candela and full spectral distribution of the luminaire are much more important than pure luminous flux or efficacy.
In short, Cree LED lights can increase the contrast between the artwork and the surrounding walls, making the color of the artwork look more vivid. Table 2 gives a brief description of the different lighting conditions caused by different luminaires. On the wall above the artwork, the average vertical illumination of the Cree LED is reduced compared to the 23W fluorescent lamp, as it concentrates more of the light on the surface of the artwork. From the contrast can be analyzed, the CFL is only 0.5, and the contrast of the LED light is 1.9, which greatly enhances the lighting effect of the artwork.
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