Spectral Design Considerations of White LED for Classroom Application

The improved efficiency of Phosphor-converted white LED devices and fixtures along with the significant cost down effort have led to tremendous market growth in almost every lighting application. However, the high-energy blue proportion of phosphor-converted white LED has raised concern about photochemically induced retinal damages. For applications such as classroom lighting, the blue light hazard reduction along with other parameters such as illuminance, illuminance uniformity, colour rendering, flicker, glare are all important considerations. In the paper, we present two different LED package designs and their spectral power distribution (SPD) characters suitable for classroom lighting. The first design uses common approach of single wavelength blue LED chip to excite multiple phosphors to achieve high colour rendering of Ra98. The second design uses two different wavelength blue LED chips combined with phosphors to further reduce the high energy blue light while maintaining colour rendering of Ra98. The LED package of the second design approach is found to be more suitable and is therefore built into fixtures and implemented in a classroom. The lighting design of the classroom using Dailux simulation tools is also presented. Key parameters are then measured to meet the lighting quality standard of GB 7793–2010 for classroom application.