The performance of white pc LEDs based on violet chips is analyzed in terms of
several metrics (lm/W, mW/lm, and package efficiency). A calculation is developed to
evaluate package efficiency using spectroradiometric measurements and accounting for
extraneous factors (Stokes' loss, luminous efficacy of the phosphor and bleed). The
method is demonstrated on a state of the art "warm white" power LED, and performance
entitlement is also discussed.
Currently, the highest color rendering index (CRI) value obtained in commercially available LED devices is around 90. This falls short of the CRI values typical for incandescent lamps (defined at 100). Similarly, the commercially available LEDs for higher color temperature have CRI values of 65-85, well below the theoretical maximum of 100. New phosphor blends are proposed for use with LED chips emitting in the 350-450 nm range. The application of such blends can afford CRI values greater than 95, over the entire range of color temperatures of interest for general illumination (2500K -
8000K). In some cases, the CRI values approach the theoretical maximum of 100. LED based lamps with a steady state performance of 23 LPW and 25 lumens per chip at 3000K, with a general CRI (Ra) of 97 and a mean CRI (R1-R14) of 96 are demonstrated.
Proc. SPIE. 5187, Third International Conference on Solid State Lighting
KEYWORDS: Near ultraviolet, Light emitting diodes, Statistical analysis, Ultraviolet radiation, Ultraviolet light emitting diodes, Monte Carlo methods, Europium, Standards development, Spectral models, RGB color model
The advantages of near UV LED chips with phosphors for white light generation are discussed. Recently developed UV LED excitable phosphor blends are presented. Monte Carlo simulations suggest low color point variation (entirely within the first MacAdam oval) for the standard LED chip bin (400-410 nm), compared to high color point variation (outside the fourth MacAdam oval) for the standard bin (460-470 nm) and typical phosphors, modeled as Gaussians of realistic spectral width and targeting the 3000K ANSI color point (x=0.440, y=0.403). A discussion of the full LED package performance is also offered.