Potential of using led modules as primary light sources for office buildings

Abstract

This paper discusses the potential of using LED modules as the primary light source for office buildings’ lighting systems. The LED lamps are the newest mass-produced lamps today; they have many insurmountable advantages compared to other light sources, like long lamp life, high efficacy, and low heat emission. Because of these advantages, owners and occupants of buildings can benefit greatly from the application of LED luminaires. The main focus of this paper is in 4 categories, which include the reliability of published data, occupant comfort, energy efficiency, and the life cycle costs of building lighting systems. LED light sources are compared to other primary light sources, which include fluorescent and incandescent lamps, of low ceiling office spaces from these 4 categories. The reliability of published data discussion covers color rendering index (CRI), correlated color temperatures (CCT), lamp life, and efficacy of the different type of lamps. The criteria of LED lamps are the most emphasized point of this section. The current CRI, efficacy, and lamp life evaluation systems are not suitable for LED lamps, and this paper discusses the practical value of each of these published data in office lighting system design. Some technical reports presented in this paper show that high CRI values of LED light sources do not directly link to excellent color rendition. However, LED light sources can have similar spectrum power distributions as natural light, and offer adequate visual comfort. Efficacy and lamp life are in the same situation. Even though, the published values do not necessarily reflect the real life performance of LED lamps, they often still have the longest lamp life and highest efficacy. Human comfort is the second factor discussed. Engineers and lighting designers consider illuminance level, color rendering ability, and glare of lighting systems to be deciding factors of human comfort from a lighting design perspective. However, many medical studies show that the human is much more sensitive to the correlated color of light sources. Light sources must vary output luminous flux and correlated color temperatures over time to help occupants reach optimum office task productivity and maintain health and visual comfort. LED lamps are the only light source that can practically change both the output luminous flux and correlate color temperature without heavy extra investments in equipment, which makes it the perfect candidate for this category. Energy efficiency is the third discussion point presented in this paper. Efficacy is a widely adopted term for evaluating the energy efficiency of a lamp, which describes the ratio of the output illuminance and input power. Because the output illuminance of LED lamps is decided not only by the illuminant bodies, but also many other electronic components in the lamps, some experts suggest that using efficacy to judge LED lamps is biased. This paper states the author’s position on whether efficacy can adequately describe the efficiency of LED lamps. Costs are also an inevitable point of this paper. LED lamps have the reputation of being the most expensive type of light source, but marketing data shows that the price of LEDs has been dropping dramatically recently. Moreover, Haitz’s law predicts that the price of LEDs will drop even more in the future. In this paper, the lifecycle costs of a light system have also been addressed across different types of light sources. Some crucial drawbacks of LED lamps, such as narrow photometric distribution and thermal damage control, are also addressed in this paper. Scientists and engineers still have not found the perfect solution to these drawbacks, but they are not significant enough to jeopardize the application of LED lamps in most architectural lighting design cases. According to the finding of this paper, LED lamps are the mainstream light source of future office lighting systems. The author also gives some suggestions for using LED lamps as primary light sources in office lighting system design applications at the end of the paper.