InGaN RGB Light-Emitting Diodes With Monolithically Integrated Photodetectors for Stabilizing Color Chromaticity

In this paper, a solution toward realizing color chromaticity stabilized InGaN red, green, and blue (RGB) light-emitting diode (LED) is proposed and demonstrated. The InGaN/GaN multiple quantum wells (play a key role in light emission from the LEDs and photodetection from the photodetectors (PDs). The spectral overlaps between the emission and absorption spectra are measured and the photocurrents of the PDs exhibit linear behavior with increasing LED driving currents. The solution involves the use of RGB chips with monolithically integrated PDs that detect the levels of light output from an individual chip in real time, whose photocurrent signals are fed to LED driver circuits that make use of the signal to provide a driving current that stabilizes the light output. Adoption of this feedback strategy results in CIE coordinates drifts of Δ(0.003, 0.005) over the 400 h duration of testing, proving to be an effective way of stabilizing color chromaticity from RGB LEDs.

I. Introduction

The efficiencies and reliabilities of gallium nitride (GaN) light-emitting diode (LED)-based solid-state lighting are widely established. While LEDs have longer lifetimes than conventional lighting technologies [1]–[3], their performances degrade over time in the forms of reduction in luminous flux as well as shifts in chromaticity coordinates and color rendering index [4]–[6]. Even though all types of lamps experience color chromaticity shift to different extents, the long-term color stabilities (defined as the maintenance of spectral power distribution over time) of LEDs raise concerns owing to their significantly longer lifetimes [7], [8]. The effects of color shifts, which affect both the color appearance of the light source and the color of objects being illumination, depend on the application and the environment for which the light source is deployed. Generally, a high degree of color stability is required for high-end applications such as medical or museum lighting [9]–[11]. For applications involving large numbers of light sources, the lack of color stability will result in nonuniform color uniformities across the surfaces being illuminated.