Expand this Topic clickable element to expand a topic
Skip to content
Optica Publishing Group
About All Issues Feature Issues

Spectral optimization of color temperature tunable white LEDs with red LEDs instead of phosphor for an excellent IES color fidelity index

Guozhao Zhang, Ke Ding, Guoxing He, and Ping Zhong

Open Access Open Access

Abstract

The optimal spectral parameters and photometric performances of white LEDs with red LEDs instead of phosphor (pc/R-WLEDs) for the color fidelity index (Rf) above 97 at correlated color temperatures (CCTs) of 2700 K to 6500 K have been obtained based on the luminous efficacy (LE) model. We have first reported four real pc/R-WLEDs with Rfs of 96–97 and LEs of 120–124 lm/W at CCTs of 2969 K, 4468 K, 5682 K, and 6558 K by using blue (448 nm) and red (650 nm) LEDs, as well as green (507 nm) and yellow (586 nm) phosphors. As compared with phosphor-converted white LEDs (pc-WLEDs) as well as quantum dots white LEDs (QD-WLED), it was found that the pc/R-WLEDs, not the QD-WLED as widely expected, make strong candidates for excellent color rendition, especially in the low color temperature range, for replacing current pc-WLEDs in the future.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

The high-efficiency hybrid white LEDs, as we known, can be divided into three categories: the phosphor-coated white LED (pc-WLED), the quantum dots white LED (QD-WLED), and pc-WLED with red LEDs instead of phosphor (pc/R-WLED). Both excellent color rendering property approached the ideal or natural light source and high efficiency have always been the goal pursued by people. Typically, the performance of hybrid white LEDs is described primarily by the general color rendering index (Ra) [1] and luminous efficacy (LE) [2]. In our previous works [3,4], the optimization of white LEDs was studied under the constraint of both a designated correlated color temperature (CCT) and Ra by maximizing radiation luminous efficacy (LER). The CCT tunable pc/R-WLEDs with the blue InGaN chip , the red AlGaInP chip, and green and yellow silicate phosphors at CCTs of 2700 to 6500 K could achieve LER higher than 296 lm/W under conditions of both Ra and R9 above 98 [3]. It was reported that QD-WLEDs with green-, yellow-, and red-emitting QDs excited by the blue LED could achieve LERs of 327–371 lm/W for Ra = 95 and R9 = 95 at CCTs of 2700 to 6500 K [4]. In order to consider the energy loss of Stokes shift, we proposed the concept of limited luminous efficacy (LLE) [5]. Some optimized hybrid white LEDs have been investigated by maximizing LLE under conditions of designated color rendering [5–9]. The CCT tunable pc/R-WLEDs with the blue chip, the red chip, and green and yellow phosphors could achieve LLEs of 276–309 lm/W for both Ra and R9 above 98 at CCTs of 2700 to 6500 K [5]. The QD-WLEDs with cyan CsPb(Cl0.1Br0.9)3, green CsPb(Br0.9I0.1)3, yellow CsPb(Br0.5I0.5)3, and red CsPb(Br0.2I0.8)3 QDs excited by the blue chip could realize CCT tunable white-lights with Ras of 96–97 and LLEs of 243–254 lm/W at CCTs of 2700 K to 6500 K [9]. The R/Y/C white LED cluster, which consists of AlGaInP red LEDs (633 nm, 20 nm), pc-Y LEDs packaged by combining silicate green (512 nm) and orange (580 nm) phosphors with the InGaN blue LED die (452.6 nm, 25.7 nm), and the pc-C LED packaged by combining silicate green (512 nm) phosphor with the same InGaN blue LED die, could realize CCT tunable white lights with Ras of 98–99, R9s of 98 and LLEs of 267–282 lm/W at CCTs of 2700 K to 6500 K. The real R/Y/C white LED cluster can realize CCT tunable white lights with Ras of 97–98, R9s of 98–99, and LEs of 122–132 lm/W at CCTs of 2731 K to 6533 K [10]. The color rendition is commonly measured by adopting Ra. One problem with Ra is that it can give fairly high scores to sources that render some saturated object colors very poorly [11,12]. Recently, the Illuminating Engineering Society of North America (IES) published a two-measure system, including a color fidelity index (Rf) and a relative color gamut index (Rg) [13] to remedy the limitations of the Ra. The Commission Internationale de l’Eclairage (CIE) has accepted the method toward international recommendation [14]. According to IES evaluation, the Rfs of pc/R-WLEDs, QD-WLEDs, and the R/Y/C white LED cluster mentioned above were less than 95. This indicates that their color rendering properties were not as high as the CIE Ra. Zhang [15] reported that the four-channel LEDs with the red, yellow, green, and blue LEDs could yield high color rendering in terms of Rf (93–94) and Ra (95–97) and relatively excellent LER (299–339 lm/W) over a wide range of CCT from 2800 K to 6500 K. The practical 17-channel LED array consisting of 13 types of narrow-band LEDs and 4 types of phosphor-converted white LEDs with Rfs of 93–97, Rgs of 100–102, and LERs of 282–312 lm/W at CCTs of 2800 to 6500 K was demonstrated [15]. It is a pity that there was no data on the luminous efficacy of the 17-channel LED array. However, the LLE is based on the hypothesis that incoming photons is equal to the emitted photons. Recently, the optimization model for LE of CCT tunable pc-WLED has been developed [16]. The optimal pc-WLEDs with green, yellow and red phosphors excited by a blue chip could achieve a Rf of 97 and LEs of 118–127 lm/W at CCTs of 2700 K to 6500 K for a radiant efficiency (Re) of the blue chip of 60% and a quantum efficiency (Qe) of phosphor layer of 90%. Four real pc-WLEDs with Rfs of 96–97 and LEs of 93–106 lm/W at CCTs of 3037 K, 4081 K, 4951 K, and 6443 K have been demonstrated [16]. In order to evaluate the photometric performance of three types of hybrid white LEDs, it is urgent to establish the LE model of pc/R-WLEDs. The spectral optimization of the CCT tunable pc/R-WLEDs by maximizing LE under a designated of Rf has not been explored until date. In this work, the model for LE of pc/R-WLED, including the Res of both blue and red LEDs, as well as the Qe of the two-color phosphor layer, was developed. The optimized spectral parameters of each color component, as well as photometric and colorimetric performances of pc/R-WLEDs for maximizing the average LE at CCTs of 2700 K to 6500 under the condition of Rf ≥ 97 were presented. Furthermore, the photometric performances of three kinds of hybrid white LEDs with a Rf of 97 were discussed in teams of the LE. Finally, four strongest candidates, pc/R-WLEDs with Rfs of 96–97 and LEs of 120–124 at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, were demonstrated.

2. Photometric optimization model

The relative spectral power distribution (SPD) of a pc/R-WLED consisting of the phosphor-coated LED (pc-LED)s with green and yellow phosphors excited by a blue LED, as well as red LEDs, Spc/R(λ), is given by,

$${\mbox{S}_{\textrm{pc/R}}}(\lambda ) = {{\mbox{k}}_{\textrm{pc}}}{{\mbox{S}}_{\textrm{pc}}}(\lambda ) + {{\mbox{k}}_\textrm{r}}{\mbox{S}}(\lambda ,{\lambda _{\rm{r}}},\Delta {\lambda _{\rm{r}}})$$
where Spc(λ) and S(λ, λr, Δλr) refer to the relative SPD of pc-LED and red LED, λr and Δλr refer to peak wavelength (WL) and a full width at half maximum (FWHM) of red LED, respectively.kpc and kr refer to proportions of the relative spectra of pc-LED and red LED, respectively. Notice that the proportion coefficients (kpc and kR) have only one independent parameter for the relative SPD of pc/R-WLED. The relative SPD of pc-LED, Spc(λ), is given by,
$${{\mbox{S}}_{\textrm{pc}}}(\lambda ) = {{\mbox{q}}_{\textrm {b}}}{\mbox{S}}(\lambda ,{\lambda _{\textrm {b}}},\Delta {\lambda _{\textrm {b}}}) + {{\mbox{q}}_{\rm{g}}}{\mbox{S}}(\lambda,{\lambda _{\rm{g}}},\Delta {\lambda _{\rm{g}}}) + {\hbox{q}_{\rm{y}}}\hbox{S}(\lambda ,{\lambda _{\rm{y}}},\Delta {\lambda _{\rm{y}}})$$
where S(λ, λb, Δλb), S(λ, λg, Δλg) and S(λ, λy, Δλy) refer to relative SPDs of the blue spectrum transmitted through phosphor layer, green and orange phosphors, respectively. λb, λg and λy refer to peak WLs of blue LED, green, and orange phosphors, respectively. Δλb, Δλg and Δλy refer to their FWHMs, respectively. qb, qg and qy are proportions of the relative spectra of the blue spectrum transmitted through phosphor layer, green and orange phosphors, respectively. Notice that the proportion coefficients (qb, qg, and qy) have only two independent parameters for the relative SPD of pc-LED. We employ Ohno model [17] of SPDs for the blue and red LEDs. The SPDs of phosphors are modeled as a Gaussian function on the photon energy scale [18]. The number of low energy photons emitted from the phosphor layer consisting of green/yellow phosphor blends per second, Np, is
$${\mbox{N}}_{\textrm{p}} = \frac{{{\mbox{k}_{\textrm{pc}}}{\mbox{q}_{\textrm{g}}}}}{{\mbox{hc}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _\textrm{g}},\Delta {\lambda _{\textrm{g}}})\lambda {\mbox{d}}\lambda } + \frac{{{\mbox{k}_{\textrm{pc}}}{\mbox{q}_{\textrm{y}}}}}{{\mbox{hc}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _{\textrm{y}}},\Delta {\lambda _{\textrm{y}}})\lambda {\mbox{d}}\lambda }$$
The number of high energy blue photons absorbed by the green/yellow phosphor layer per second, Nab, is
$${\mbox{N}_{\textrm {ab}}} = \frac{{{{\mbox{q}}_{\textrm {ab}}}}}{{\mbox{hc}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _{\textrm {b}}},\Delta {\lambda _{\textrm {b}}})\lambda {\mbox{d}}\lambda }$$
where qab, h and c refer to the absorbed proportion of the blue light, Planckian constant, and light speed, respectively. The Qe of the green/yellow phosphor layer is defined as Np/Nab, so the absorbed proportion, qab, can be calculated as follows:
$${{\mbox{q}}_{\textrm {ab}}} = \frac{{{{\mbox{k}}_{\textrm{pc}}}{{\mbox{q}}_{\textrm{g}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _{\textrm{g}}},\Delta {\lambda _{\textrm{g}}})\lambda {\mbox{d}}\lambda } + {{\mbox{k}}_{\textrm{pc}}}{{\mbox{q}}_{\textrm{y}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _{\textrm{y}}},\Delta {\lambda _{\textrm{y}}})\lambda {\mbox{d}}\lambda } }}{{{\mbox{Q}_{\textrm{e}}}\int_\lambda {{\mbox{S}}(\lambda ,{\lambda _{\textrm {b}}},\Delta {\lambda _{\textrm {b}}})\lambda {\mbox{d}}\lambda } }}$$
The radiant efficiency of the blue LED, Re,b, is
$${\mbox{R}_{\textrm{e,b}}} = \frac{1}{{{\mbox{P}_{\textrm{in,b}}}}}\int_\lambda {({\mbox{k}_{\textrm{pc}}}{{\mbox{q}}_{\textrm {b}}} + {{\mbox{q}}_{\textrm {ab}}}){\mbox{S}}(\lambda ,{\lambda _{\textrm {b}}},\Delta {\lambda _{\textrm {b}}}){\mbox{d}}\lambda }$$
The radiant efficiency of the red LED, Re,r, is
$${\mbox{R}_{\textrm{e,r}}} = \frac{1}{{{\mbox{P}_{\textrm{in,r}}}}}\int_\lambda {{\mbox{k}_\textrm{r}}{\mbox{S}}(\lambda ,{\lambda _{\textrm{r}}},\Delta {\lambda _{\textrm{r}}}){\mbox{d}}\lambda }$$
where Pin,b and Pin,r refer to the normalized input power of blue and red LEDs, respectively. So the LE of a pc/R-WLED, including the radiant efficiency of both blue and red LEDs, as well as the quantum efficiency of the green/yellow phosphor layer, can be calculated by
$$\begin{aligned}\mbox{LE} &= \frac{{683}}{{({{\mbox{P}}_{{\textrm{inb}}}} + {{\mbox{P}}_{{\textrm{inR}}}})}}\int_\lambda {{\mbox{V}}(\lambda ){{\mbox{S}}_{\textrm{pc}/\mbox{R}}}(\lambda ){\mbox{d}}\lambda } \\&= \frac{{683\int_\lambda {{\mbox{V}}(\lambda ){{\mbox{S}}_{\textrm{pc}/\textrm{R}}}(\lambda ){\mbox{d}}\lambda } }}{{\frac{1}{{{{\mbox{R}}_{{\textrm{e}},{\textrm{b}}}}}}\int_\lambda {({\mbox{k}_{\textrm{pc}}}{{\mbox{q}}_{\textrm {b}}} + {\mbox{q}_{\textrm {ab}}}){\mbox{S}}(\lambda ,{\lambda _{\textrm {b}}},\Delta {\lambda _{\textrm {b}}}){\mbox{d}}\lambda } + \frac{1}{{{{\mbox{R}}_{{\textrm{e}},{\textrm{r}}}}}}\int_\lambda {{{\mbox{k}}_{\textrm{r}}}{\mbox{S}}(\lambda ,{\lambda_{\textrm{r}}},\Delta {\lambda _{\textrm{r}}}){\mbox{d}}\lambda } }} \end{aligned}$$
where V(λ) is 1988 CIE photopic luminous efficiency function. In order to optimize spectra of CCT tunable pc/R-WLEDs, we introduce the average LE of CCT tunable pc/R-WLEDs with both blue and red LEDs (Re,b = Re,r = 60%) as well as the green/yellow phosphor layer (Qe = 90%) under the condition of Rf ≥ 97 as an objective function F:
$$\begin{aligned}{\mbox{F}} = \sum\limits_{{\textrm{j}} = 1}^8 {\mbox{LE}_\textrm{j}} (& {\mbox{k}_{{\textrm{r}},{\textrm{j}}}},{\lambda _{\textrm{b}}},{\lambda_{\textrm{g}}},{\lambda _\textrm{y}},{\lambda _\textrm{r}},\Delta {\lambda _\textrm{b}},\Delta {\lambda _{\textrm{g}}},\Delta {\lambda _{\textrm{y}}},\Delta {\lambda _{\textrm{r}}}) \\ & ({\mbox{for R}}_{\textrm{f}} \ge 97,{\mbox{D}_{\textrm{uv}}} = 0) \end{aligned}$$
where the subscripts j = 1, 2, 3, 4,5, 6, 7, and 8 refer to 2700, 3000, 3500, 4000, 4500, 5000,5700, and 6500 K of CCTs, respectively. The chromaticity of hybrid white LEDs were constrained to lie along the Planckian locus for CCT below 5000 K, or the daylight locus for CCT above 5000 K, that is, the chromaticity difference from the Planckian or daylight locus on the CIE 1960 uv chromaticity diagram (Duv) is equal to zero. The reason for a limit of Duv = 0 is to avoid going out of the range of the chromaticity tolerance quadrangles of white-light sources [19] due to the deviations of peak WLs and FWHMs of LEDs and phosphors [20]. For the pc/R WLED, the chosen WLs are varied between450 nm and 470 nm for the blue LED, between 490 nm and 550 nm for the green phosphor, between 550 nm and 600 nm for the yellow phosphor, and between 600 nm and 650 nm for the red LED in our optimization. In addition, the FWHMs are varied between 25 nm and 35 nm for blue LED, between 70 nm and 120 nm for green and yellow phosphors, and between for 20 nm and 30 nm red LEDs. Subjecting the 12-dimensional parameter space to three color-mixing constrains results in the location of the feasible vectors on the hyper surface with 9 dimensionalities [21] so that the objective function F does not include the parameters kpc, qb, qg and qy. Hence the optimization problem reduces to finding maximum of the objective functions (F). In optimization, a fast Pareto genetic algorithm [22] is chosen because it is able to scan a vast set of solutions, does not depend on a starting solution, is useful for complex problems, and most importantly can be easily modified to estimate the Pareto optimal set.

3. Results and discussion

The optimal spectral parameters of each color component and the photometric performances of CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700 K to 6500 K (Duv = 0) have been obtained by nonlinear program for maximizing F. The optimal peak WLs of blue LED, green phosphor, yellow phosphors and red LED are 443.4 nm, 505.3 nm, 584.2 nm and 642.6 nm, respectively. Their optimal FWHMs are 35.0 nm, 70.0 nm, 85.0 nm, and 30.0 nm, respectively. The optimal proportions (qs, ks), relative radiation fluxes (Φes%) of the blue LED, the green phosphor, the yellow phosphor and the red LED, as well as photometric and colorimetric performance are shown in Table 1, where the relative radiant flux (Φe) of each color component replaces the proportion (qs, ks) to facilitate the adjustment of each color composition in practical application. The results show that the Φe increases as CCT increases for blue and green components, and decreases as CCT increases for yellow and red components. Table 1 indicates that pc/R-WLEDs with could realize white lights with Ras of 98–99, Rfs of 97, Rgs of 100–102, and Rf,skins (average of the CES15 and CES18 samples representing human skin tones) [12] of 98–99, LERs of 282–307 lm/W, and LEs of 136–146 lm/W at CCTs of 2700 to 6500 K for Re,b= Re,,r =60% and Qe = 90%. The optimal SPDs of CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700 K to 6500 K are shown in Fig. 1. The Rf, hues for 16 hue bins [13] of the optimal CCT tunable pc/R-WLEDs with Rf ≥ 97at CCTs of 2700 K to 6500 K are shown in Fig. 2. The results show that Rf, hues are higher than 92.2 for 16 hue bins at CCTs of 2700 K to 6500 K. So the pc/R-WLEDs with the blue LED (443.4 nm, 35.0 nm), the green (505.3 nm, 70.0 nm) and the yellow (584.2 nm, 85.0 nm) phosphors, as well as the red LED (642.6 nm, 30.0 nm) could achieve CCT tunable white lights with excellent color rendering properties and high luminous efficacy.

Tables Icon

Table 1. qs, ks, Φes of each color component, Ras, Rfs, Rgs, Rf, skins, LERs, and Les of the optimal CCT tunable pc/R-WLEDs at CCTs of 2700 K to 6500 K for Re,b = Re,r = 60% and Qe = 90%.

View Table | View all tables in this article
 figure: Fig. 1.

Fig. 1. SPDs of the optimal CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700 – 6500 K (Duv = 0).

Download Full Size | PDF

 figure: Fig. 2.

Fig. 2. Rf, hues for 16 hue bins of the optimal CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700- 6500 K (Duv = 0).

Download Full Size | PDF

Compared with the R/Y/C LED cluster [10] with Rfs of 91–92 (according to the IES evaluation results), the Rf of pc/R-WLEDs are higher than that of the R/Y/C LED cluster, although the Ra of pc/R- WLEDs are almost the same as that of the R/Y/C LED cluster. This indicates that color rendering properties of pc/R-WLEDs are higher than the R/Y/C LED cluster. So the CCT tunable pc/R-WLEDs with Rfs of 97 require shorter peak WL of blue LED and longer peak WL of red LED. Both the shortening of WL for the blue components and the lengthening of WL for the red components indicate the broadening of the spectral range. It is due to the wide spectrum distribution that the natural colors of the samples are reproduced better.

To compare LEs of the pc-WLED, the QD-WLED and the pc/R-WLED, the luminous efficacy ratios of the pc/R-WLEDs with pc-WLEDs and QD-WLEDs [16] for Qe = 90% at CCTs of 2700 K to 6500 K under a condition of Rf ≥ 97, LEpc/R/LEpc and LEpc/R/LEQD, are shown in Table 2, where both LEpc/R/LEpc and LEpc/R/LEQD are independent of Re, assuming the same Re of blue and red LEDs. The results show that both LEpc/R/LEpc and LEpc/R/LEQD increase as CCT decreases, and that the LEs of optimal pc/R-WLEDs will be higher than the optimal pc-WLEDs by 9%–23%, and higher than the optimal QD-WLEDs by 6%–18% for Qe = 90%. It is suggested that the pc/R-WLED optimized by LE make strong candidates, especially in low color temperature range, for replacing current pc-WLED in the future. At the same time, it also shows that the QD-WLED is not a candidate with strong competitiveness for excellent color rendition due to the LE of the QD-WLED slight higher than pc-WLED [16] as well as greatly lower than pc/R-WLED.

Tables Icon

Table 2. Luminous efficacy ratios of the pc/R-WLEDs with the pc-WLEDs and QD-WLEDs [16], LEpc/R/LEpc and LEpc/R/LEQD, for Qe = 90% at CCTs of 2700 K to 6500 K under Rf ≥ 97.

View Table | View all tables in this article

According to the optimal spectral parameters, four real pc/R-WLEDs at CCTs of 2969 K, 3955 K, 5034 K, 6558 K were demonstrated. Four real pc-LEDs with the different G1758 (507 nm, 67 nm) and O5446 (586 nm, 85 nm) phosphors (Intematix Corporation) densities in silicone excited by the InGaN blue LED (448 nm, 30 nm), as well as the AlGaInP red LED (650 nm, 25 nm) were fabricated, respectively. The SPDs, the luminous flux (Φ) and the input power (Pin) of both the pc-LED and the red LED at different drive currents (IF) were measured by an automated photometric/radiometric measurement setup (EVERFINE Corporation)and a power meter at an temperature of 25°C. The automated photometric/radiometric measurement setup contains a spectroradiometer (HAAS-2000), an integrating sphere (0.5 m), a LED adapter with a temperature controller (TC-100) and a digital power meter (PF9800). The LED was placed inside the integrator sphere and fixed on the LED adapter with the TC-100 temperature controller. The real pc/R-WLED consists of a pc-LED and a red LED. The forward current of red LED (IF, red) is 50 mA, and the forward current of pc-LED (IF, pc) according to requirements of CCT of the pc/R-WLED can be predicted by using He-Zheng model [23]. The photometric and colorimetric performances of four real pc/R-WLEDs at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K are shown in Table 3. The Rf, hues for 16 hue bins of four real pc/R-WLEDs are shown in Fig. 3.

Tables Icon

Table 3. Photometric and colorimetric performances of four real pc/R-WLEDs consisting of different pc-LED and an AlGaInP red LED under the forward current of 50 mA at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively.

View Table | View all tables in this article
 figure: Fig. 3.

Fig. 3. Rf, hues for 16 hue bins of four real pc/R-WLEDs at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively.

Download Full Size | PDF

The SPDs of four real pc/R-WLEDs and pc-LEDs, as well as the red LED are shown in Fig. 4. The experimental results show that four real pc/R-WLEDs can realize white lights with Ras of 98–99, Rfs of 96–97, Rgs of 101, Rf, skins of 97–98, LERs of 280–295 lm/W, and LEs of 120–124 lm/W, as well as their Rf, hues for 16 hue bins are above 90.2 at CCTs of 2969 K to 6558 K, and that LEs of the four real pc/R-WLEDs are higher than that of pc-WLEDs by 14%–33% [15]. Because peak WLs and FWHMs of the actual LEDs and phosphors are different from the optimal ones resulting in the different relative radiation fluxes of the LEDs and phosphors, there are larger differences between real SPD and optimal one, but the color rendering properties of the real pc/R-WLEDs are very close to that of the optimal one. For Rf = 96 at CCTs of 2969 K to 6558 K, the WL of real red LED needs to reach about 650 nm. The longer WL of red LED reduces the LER of pc/R-WLED, and that leads to the reduction of luminous efficacy. The pc-LED and red LED in the pc/R-WLEDs will exhibit different long-term degradation rates that will change the resulting SPD of the pc/R -WLED as well as CCT, however those changes could be solved by adjusting forward currents of LEDs according to the ratio of their light intensity which could be measured by an auxiliary detector in the pc/R-WLED.

 figure: Fig. 4.

Fig. 4. SPDs of four real pc/R-WLEDs consisting of different pc-LEDs under IF,pcs of 117 mA, 178 mA, 238 mA, and 316 mA, as well as a AlGaInP red LED under the forward current of 50 mA at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively. The inset shows photographs of white light of the real pc/R WLED from the integrating sphere with a increase in the CCT from top to bottom.

Download Full Size | PDF

4. Conclusions

The pc/R-WLEDs with the blue LED (443.4 nm, 35 nm), the green (505.3 nm, 70 nm) and the yellow (584.2 nm, 85 nm) phosphors, as well as the red LED (642.6 nm, 30 nm) could achieve tunable CCT white lights with Ras of 98–99, Rfs of 97, Rgs of 100–102 and Rf, skins of 98–99,and LEs of 136–146 lm/W at CCTs of 2700 to 6500 K for Re,b = Re,r = 60% and Qe = 90%. The LEs of the optimal pc/R-WLEDs will be higher than the optimal pc-WLEDs by 9%–23%, and higher than the optimal QD-WLEDs by 6%–18% for Qe = 90%. Four real pc/R-WLEDs consisting of two pc-LEDs with different G1758(507 nm, 67 nm) and O5446 (586 nm, 85 nm) phosphors (Intematix Corporation)densities in silicone excited by the InGaN blue LED (448 nm, 30 nm) under IF,pcs of 117 mA, 178 mA, 238 mA, and 316 mA, as well as one AlGaInP red LEDs (650 nm, 25 nm) under IF,red of 100 mA can realize white lights with Ras of 98–99, Rfs of 96–97, Rgs of 101, Rf, skins of 97–98, and LEs of 120–124 lm/W, as well as their Rf, hues for 16 hue bins are above 90.2at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively. It is suggested that the pc/R-WLED make strong candidates, especially in low color temperature range, for replacing current pc-WLED in the future.

Funding

National Natural Science Foundation of China (NSFC) (51575099).

References

1. Commission Internationale de l’Eclairage, “Method of measuring and specifying colour rendering properties of light sources,” CIE 13.3-1995 (CIE Central Bureau, Vienna, 1995).

2. Commission Internationale de l’Eclairage, “ILV: International Lighting Vocabulary,” CIE S 017/E: 2011, (CIECentral Bureau, Vienna, 2011).

3. G. X. He and H. F. Yan, “Optimal spectra of the phosphor-coated white LEDs with excellent color rendering property and high luminous efficacy of radiation,” Opt. Express 19(3), 2519–2529 (2011). [CrossRef]  

4. P. Zhong, G. X. He, and M. H. Zhang, “Optimal spectra of white light-emitting diodes using quantum dot nanophosphors,” Opt. Express 20(8), 9122–9134 (2012). [CrossRef]  

5. G. X. He and J. Tang, “Spectral optimization of color temperature tunable white LEDs with excellent color rendering and luminous efficacy,” Opt. Lett. 39(19), 5570–5573 (2014). [CrossRef]  

6. G. X. He and J. Tang, “Spectral optimization of phosphor-coated white LEDs for color rendering and luminous efficacy,” IEEE Photon. Technol. Lett. 26(14), 1450–1453 (2014). [CrossRef]  

7. W. Yang, P. Zhong, S. L. Mei, Q. H. Chen, W. L. Zhang, J. T. Zhu, R. Q. Guo, and G. X. He, “Photometric optimization of color temperature tunable quantum dots converted white LEDs for excellent color rendition,” IEEE Photon. J. 8(5), 1–11 (2016). [CrossRef]  

8. W. Yang, G. X. He, S. L. Mei, J. T. Zhu, W. L. Zhang, Q. H. Chen, G. L. Zhang, and R. Q. Guo, “Controllable synthesis of dual emissive Ag:InP/ZnS quantum dots with high fluorescence quantum yield,” Appl. Surf. Sci. 423, 686–694 (2017). [CrossRef]  

9. W. L. Zhang, W. Yang, P. Zhong, S. L. Mei, G. L. Zhang, G. P. Chen, G. X. He, and R. Q. Guo, “Spectral optimization of color temperature tunable white LEDs based on perovskite quantum dots for ultrahigh color rendition,” Opt. Mater. Express 7(9), 3065–3067 (2017). [CrossRef]  

10. D. Y. Lin, P. Zhong, and G. X. He, “Color temperature tunable white LED cluster with color rendering index above 98,” IEEE Photon. Technol. Lett. 29(12), 1050–1053 (2017). [CrossRef]  

11. N. Narendran and L. Deng, “Color rendering properties of LED light sources,” Proc. SPIE 4776, 61–67 (2002). [CrossRef]  

12. N. Sándor and J. Schanda, “Visual colour rendering based on colour difference evaluations,” Light. Res. Technol. 38(3), 225–239 (2006). [CrossRef]  

13. Illuminating Engineering Society of North America, IES method for evaluating light source color rendition, IES TM-30-15, (IESNA, 2015).

14. Commission Internationale de l’Eclairage, CIE 224:2017 CIE 2017 Colour Fidelity Index for accurate scientific use, January 4, 2017 (CIE Central Bureau, Vienna, 2017).

15. F. Zhang, H. Xu, and Z. Wang, “Optimizing spectral compositions of multichannel LED light sources by IES color fidelity index and luminous efficacy of radiation,” Appl. Opt. 56(7), 1962–1971 (2017). [CrossRef]  

16. W. J. Gao, K. Ding, G. X. He, and P. Zhong, “Color temperature tunable phosphor-coated white LEDs with excellent photometric and colorimetric performances,” Appl. Opt. 57(31), 9322–9327 (2018). [CrossRef]  

17. Y. Ohno, “Spectral design considerations for white LED color rendering,” Opt. Eng. 44(11), 111302 (2005). [CrossRef]  

18. S. J. Rosenthal, “Bar-coding biomolecules with fluorescent nanocrystals,” Nat. Biotechnol. 19(7), 621–622 (2001). [CrossRef]  

19. American National Standard, American National Standard for Electric Lamps, ANSIC78.377 (American National Standards Institute, 2008).

20. Y. Lin, Y. L. Gao, Y. J. Lu, L. H. Zhu, Y. Zhang, and Z. Chen, “Study of temperature sensitive optical parameters and junction temperature determination of light-emitting diodes,” Appl. Phys. Lett. 100(20), 202108 (2012). [CrossRef]  

21. I. Mereno and U. Contreras, “Color distribution from multicolor LED arrays,” Opt. Express 15(6), 3607–3618 (2007). [CrossRef]  

22. E. Hamidreza and D. G. Christopher, “A fast Pareto genetic algorithm approach for solving expensive multiobjective optimization problems,” J. Heuristics 14(3), 203–241 (2008). [CrossRef]  

23. G. X. He and L. H. Zheng, “White-light LED clusters with high color rendering,” Opt. Lett. 35(17), 2955–2957 (2010). [CrossRef]  

Cited By

Optica participates in Crossref's Cited-By Linking service. Citing articles from Optica Publishing Group journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (4)
Fig. 1.
Fig. 1. SPDs of the optimal CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700 – 6500 K (Duv = 0).

View in Article | Download Full Size | PDF

Fig. 2.
Fig. 2. Rf, hues for 16 hue bins of the optimal CCT tunable pc/R-WLEDs with Rf ≥ 97 at CCTs of 2700- 6500 K (Duv = 0).

View in Article | Download Full Size | PDF

Fig. 3.
Fig. 3. Rf, hues for 16 hue bins of four real pc/R-WLEDs at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively.

View in Article | Download Full Size | PDF

Fig. 4.
Fig. 4. SPDs of four real pc/R-WLEDs consisting of different pc-LEDs under IF,pcs of 117 mA, 178 mA, 238 mA, and 316 mA, as well as a AlGaInP red LED under the forward current of 50 mA at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively. The inset shows photographs of white light of the real pc/R WLED from the integrating sphere with a increase in the CCT from top to bottom.

View in Article | Download Full Size | PDF

Tables (3)

Tables Icon

Table 1. qs, ks, Φes of each color component, Ras, Rfs, Rgs, Rf, skins, LERs, and Les of the optimal CCT tunable pc/R-WLEDs at CCTs of 2700 K to 6500 K for Re,b = Re,r = 60% and Qe = 90%.

View Table | View all tables in this article
Tables Icon

Table 2. Luminous efficacy ratios of the pc/R-WLEDs with the pc-WLEDs and QD-WLEDs [16], LEpc/R/LEpc and LEpc/R/LEQD, for Qe = 90% at CCTs of 2700 K to 6500 K under Rf ≥ 97.

View Table | View all tables in this article
Tables Icon

Table 3. Photometric and colorimetric performances of four real pc/R-WLEDs consisting of different pc-LED and an AlGaInP red LED under the forward current of 50 mA at CCTs of 2969 K, 3955 K, 5034 K, and 6558 K, respectively.

View Table | View all tables in this article

Equations (9)

Equations on this page are rendered with MathJax. Learn more.

S pc/R ( λ ) = k pc S pc ( λ ) + k r S ( λ , λ r , Δ λ r )
S pc ( λ ) = q b S ( λ , λ b , Δ λ b ) + q g S ( λ , λ g , Δ λ g ) + q y S ( λ , λ y , Δ λ y )
N p = k pc q g hc ∫ λ S ( λ , λ g , Δ λ g ) λ d λ + k pc q y hc ∫ λ S ( λ , λ y , Δ λ y ) λ d λ
N ab = q ab hc ∫ λ S ( λ , λ b , Δ λ b ) λ d λ
q ab = k pc q g ∫ λ S ( λ , λ g , Δ λ g ) λ d λ + k pc q y ∫ λ S ( λ , λ y , Δ λ y ) λ d λ Q e ∫ λ S ( λ , λ b , Δ λ b ) λ d λ
R e,b = 1 P in,b ∫ λ ( k pc q b + q ab ) S ( λ , λ b , Δ λ b ) d λ
R e,r = 1 P in,r ∫ λ k r S ( λ , λ r , Δ λ r ) d λ
LE = 683 ( P inb + P inR ) ∫ λ V ( λ ) S pc / R ( λ ) d λ = 683 ∫ λ V ( λ ) S pc / R ( λ ) d λ 1 R e , b ∫ λ ( k pc q b + q ab ) S ( λ , λ b , Δ λ b ) d λ + 1 R e , r ∫ λ k r S ( λ , λ r , Δ λ r ) d λ
F = ∑ j = 1 8 LE j ( k r , j , λ b , λ g , λ y , λ r , Δ λ b , Δ λ g , Δ λ y , Δ λ r ) ( for R f ≥ 97 , D uv = 0 )
Select as filters
Select Topics Cancel
Top
       
© Copyright 2024 | Optica Publishing Group. All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies.
Privacy | Terms of Use