Introduction to KSF Phosphor LEDs & Luminus LUX COBs

KSF (Potassium Fluorosilicate (PFS), K₂SiF₆: Mn⁴⁺) phosphor* is a red powder engineered to emit a narrow-band spectrum around 630 nm when illuminated with blue light. It’s used in the packaging of high-color-gamut liquid crystal LED-based display backlights and high-color-rendering white LEDs. It is reliable and long-lasting: “the red KSF phosphor is an excellent narrow-band color converter.”[1] It emits five peaks in the red spectrum, each exhibiting “an ultra-narrow 5-nm FWHM”[1] (see Figure 1) with the main peak centered around 631 nm. “It is a stable material under high light flux and high temperature conditions.” [1]

Red KSF phosphor technology is a cutting-edge advancement used in the development of high-CRI and high-efficacy white LEDs.[2] The primary goal of this technology is to improve the quality and efficacy of white light produced by LEDs for a wide range of applications, particularly those requiring accurate color rendering and energy efficiency. KSF phosphors are new in commercial white LED technology and have significant advantages over traditionally employed nitride-based red phosphors. The KSF phosphor provides high efficacy and highly visible saturated red in LEDs and has no self-absorption, as shown in Figure 1. [3]

Figure 1. The spectral power distribution (SPD) of KSF phosphor demonstrates its unique narrow-band intensity in the red spectral region between 600 and 650 nm. The excitation curve is completely separated from the emission curve, so KSF has no self-absorption.

White LEDs with KSF phosphors are specially blended to produce a light source with a high CRI and high R9 (red) values to give illuminated objects very high color realism with less energy expenditure.

By replacing the red emitting nitride phosphor with KSF phosphor, the color quality of 80 CRI white LEDs can be improved to 90 CRI while maintaining a similar LED efficacy. The narrow red spectrum contributed by the KSF phosphor increases red light efficacy (lm/W) by moving the radiant power in the SPD from the barely visible long wavelength tail of typical nitride-based red phosphors to a more visible wavelength range.

Adding KSF to a 3000K 90 CRI LED phosphor blend increases the Luminous Efficacy of Radiation (LER)** from 283 lm/W to 334 lm/W. Nitride phosphors have broad red emission bands that extend considerably beyond the visible range, lowering their attainable luminous efficacy of radiation.

Figure 2 illustrates the strategy to increase the LPW (Lumens per Watt) of a 3000K 90 CRI LED while maintaining CRI quality. This is achieved by replacing most of the nitride red phosphor components (blue line) with a blend of red KSF phosphor and some nitride, resulting in the desired spectral shape in the 530 – 600 nm region (red line). Nitride phosphors emit a significant amount of invisible light, whereas the KSF spectra only emit visible light. By reducing the invisible light component, the LER is increased as shown.

Figure 2. Increasing LPW of a 3000K 90 CRI LED while maintaining CRI quality.

Product Features of Luminus LUX Series COB LEDs with KSF Phosphor

Harnessing the cutting-edge KSF phosphor technology, Luminus has developed the LUX COB (chip-on-board) LED (Light Emitting Diode) product line. This innovation enables Luminus to provide a multitude of performance and efficiency benefits. The product’s notable features encompass:

• High Lumen Output and Efficacy: The LUX COBs distinguish themselves by achieving high efficacy at both 90 and 95 CRI (Color Rendering Index), mirroring that of an equivalent 80 CRI conventional white LED. This heightened efficacy enables the utilization of superior light sources in high CRI applications where energy consumption is also a critical concern.
• Wide Range of CCTs: The LUX COBs are offered across a span of correlated color temperatures (CCTs): 2400K, 2700K, 3000K, 3500K, 4000K, 5000K, and 6500K. These options come with exceptional color rendering and the exceptional white light quality that customers have come to associate with Luminus LEDs:
  • At least 90 CRI for the complete LUX COB series.
  • Typically, 97 CRI for 2700K through 5000K color temperatures.
  • Adherence to a 3 SDCM and 2 SDCM color binning standard.
• Outstanding Color over Angle Performance: The KSF phosphor-based LUX products exhibit superior optical emission uniformity and consistency of color across optics with different beam angles.
• Enhanced Thermal Conductivity: The LUX COB boasts exceptional thermal conductivity, ensuring efficient heat extraction.
• Eco-Friendly: These products are environmentally conscious, and comply with both RoHS and REACH regulations.
• Licensed IP: Luminus has secured the licensing of the innovative TriGain® PFS/KSF phosphors originally patented by General Electric (GE) for integration into our LUX COB product line. This GE-developed phosphor (now a product of Current Lighting Solutions) was chosen due to exceptional performance.

This integration of KSF phosphors into the LUX COB product line underscores Luminus’ commitment to pushing the boundaries of lighting technology and providing customers with advanced solutions that excel in performance, efficiency, and environmental responsibility.

NOTES:

* A potassium fluorosilicate (PFS)-based phosphor patented by GE Lighting as part “of its TriGain^® family of potassium fluorosilicate (PFS)-based phosphors for LED-based backlighting in displays, along with a broader licensing program for packaged LED manufacturers. The PFS technology enables LCD-based TVs, monitors, and mobile devices to produce richer reds with truer color control.” [4] KSF and PFS are equivalent terms. Both are abbreviations for K₂SiF₆: Mn⁴⁺.

** Luminous Efficacy of Radiation (LER) refers to the number of lumens produced by an LED per optical watt it generates (the ratio of its luminous flux to its optical radiation power). This value remains constant for each specific spectral power distribution (SPD) used as an input. When the same SPD shape is applied at different optical power levels, the LER remains unchanged. LER is quantified in units of lm/optical watt to convert between lumens and optical power output for an LED. It's important to note that LER only changes if there is an alteration in the SPD shape.

For more information about KSF Phosphors and Luminus’ LUX Series COB LEDs with KSF phosphor technology, read the white paper:  LUX Series COBs: Achieving High CRI Lighting with High Efficacy Using Luminus LUX Technology.

REFERENCES:

[1]         Ghaffarzadeh, K., “Phosphors or QDs for color conversion in LCD and microLED?” Wevolver, August 16, 2022.

[2]         Cohen, W.E., et al., “Review—The K₂SiF₆:Mn⁴⁺ (PFS/KSF) Phosphor”, ECS Journal of Solid State Science and Technology, 12 076004, 2023. DOI: 10.1149/2162-8777/ace47a

[3]         Setchell, J., “Chapter 4: Colour description and communication,” pages 99-129 in Colour Design (Second Edition), Janet Best (Ed.), Woodhead Publishing, 2012. DOI: 10.1016/B978-0-08-101270-3.00004-7

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