Energy-saving quality road lighting with colloidal quantum dot
nanophosphors
Talha Erdem,1 Yusuf Kelestemur,1 Zeliha Soran-Erdem,1 and Hilmi Volkan Demir1,2,*
1
Department of Electrical and Electronics Engineering, Department of Physics, and UNAM–Institute
of Materials Science and Nanotechnology, Bilkent University, Ankara, 06800, Turkey
2
School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences,
Nanyang Technological University, Singapore 639798, Singapore
*E-mail: volkan@stanfordalumni.org
Supplementary Information
1 Calculation methodology of mesopic luminance
The mesopic luminance (Lmes) is calculated according to CIE 191:2010 report [1], and defined for the
photopic luminance levels between 0.005 and 5 cd/m2. The eye sensitivity function for the mesopic
regime is defined as the linear combination of the photopic and scotopic eye sensitivity functions
given in Equation (S1) and the mesopic luminance is calculated by Equation (S2).
M (m)Vmes ()  mV ()  (1  m)V '()
(S1)
Lmes  683 / Vmes ( 0 )  Vmes () P()d 
(S2)
where V(), V'() and Vmes() are the photopic, scotopic, and mesopic eye sensitivity
functions, respectively; P() is the spectral radiance, M(m) is a normalization constant such
that Vmes() has the maximum value of 1, 0 is 555 nm, and m is a coefficient that depends on
the visual adaptation conditions. In this work, we use this most recently adapted mesopic
photometry system for the evaluation of QD-WLED based road lighting.
[1] CIE Technical Report 191:2010. Recommended system for mesopic photometry based on
visual performance. (CIE Central Bureau, Vienna, Austria, 2010).
S1
2 Computational methodology
In this study, the color converting white LED was modeled to be comprised of a blue LED
pumping the QDs which convert the blue light to green, yellow, and red light generating the
white light spectrum. The emission spectra were modeled to be Gaussian type for each color
component, i.e., blue, green, yellow, and red. In the first step of simulations, we varied the
blue wavelengths between 440 and 490 nm, the green between 500 and 540 nm, the yellow
between 550 and 590 nm, and the red between 600 and 640 nm, all with a 10 nm step size.
Totally, 750 wavelength combinations were generated. The blue component was intentionally
included to the design in order to obtain the information about required spectral features of the
blue LED so that the blue LEDs specific to street lighting can be produced. In addition, we
changed the full-width at half maximum (Δλ) of each of the Gaussian-type spectra between 30
and 45 nm with a 5 nm step size. These Δλ combinations constituted 256 cases. Moreover, the
amplitude of the color components were varied over 0, 1, 2, and 3 units and then normalized
to 1000. As a result, 529 amplitude combinations were obtained. In total, 101,568,000
(750×529×256) QD-WLED designs were generated and the Lmes and CQS thresholds
mentioned above were applied. To examine whether a wavelength step size of 10 nm is
sufficient, we performed additional simulations around the average wavelengths with a 5 nm
step size and also further with 2.5 nm. For each of the cases, 81 wavelength combinations
were obtained and the resulting number of spectrum combinations became 10,969,344
(81×529×256). These simulations indicate that the results obtained with a wavelength step
size of 10 nm are in good agreement with those of 5 and 2.5 nm step sizes. Therefore, for
understanding the required spectral conditions we used the first simulations. On the other
hand, it is quite possible to miss the spectrum possessing the highest Lmes with a wavelength
step size of 10 nm. To reveal this information we followed another 3-step methodology. In
this case, we carried out simulations around the wavelength combination giving the highest
S2
Lmes with 5 nm step size following the first experiment. Subsequently, the third step of the
simulations was carried out around the wavelength combinations of the previous step giving
the highest Lmes, this time with the 2.5 nm wavelength step size. As in the previous cases,
10,969,344 (81×529×256) spectrum combinations were tested in the last two steps of the
simulations at all of the six radiance levels.
3 Results
Table S1. Spectral parameters of QD-WLEDs resulting in the highest Lmes for all the four mesopic
road lighting standards, and for scotopic and photopic vision regimes. : peak emission wavelength,
: FWHM and α: relative amplitudes of color components of blue (b), green (g), yellow (y), and red
(r).
λ (nm)
Δλ (nm)
α (1/1000)
b
g
y
r
b
g
y
r
b
g
y
r
Scotopic
462.5
522.5
577.5
617.5
30
35
30
30
267
267
200
267
Mesopic 1
460.0
522.5
555.0
610.0
30
45
45
30
167
167
167
500
Mesopic 2
460.0
515.0
550.0
610.0
35
35
35
30
125
125
250
500
Mesopic 3
460.0
515.0
550.0
610.0
35
35
35
30
125
125
250
500
Mesopic 4
460.0
517.5
555.0
612.5
35
35
40
30
125
125
250
500
Photopic
462.5
522.5
555.0
612.50
30
40
30
30
125
125
250
500
Table S2. Radiance (P), photopic luminance (Lp), mesopic luminance (Lmes), CRI, CQS, and
correlated color temperature (CCT) of the QD-WLED spectra exhibiting the highest mesopic
luminance for the simulated four mesopic road lighting standards, and scotopic and photopic vision
regimes.
P (mW m-2sr-1)
Lp (cd/m2)
Lmes (cdmes/m2)
CRI
CQS
CCT (K)
Scotopic
1.50×10-2
0.005
0.098
85.0
88.4
4969
Mesopic 1
1.47
0.577
0.625
85.8
85.1
3417
Mesopic 2
2.36
0.932
0.980
85.9
85.1
3243
Mesopic 3
3.39
1.340
1.393
85.9
85.1
3243
Mesopic 4
4.74
1.886
1.930
86.1
85.2
3164
Photopic
13.6
5.386
5.386
87.1
85.3
3033
S3
Table S3. Required radiance of the conventional source (Pconv) such that it can generate the equal
amount of mesopic luminance (Lmes) that the QD-WLED generates and the radiance of QD-WLED is
required (PQD-WLED) for generating the designated Lmes.
Scotopic
Lmes
(cd/m2)
0.098
PCWFL
(W m-2sr-1)
PHPS
(W m-2sr-1)
3.7×10-5
PMH
(W m-2sr-1)
2.2×10-5
PQD-WLED
(W m-2sr-1)
1.5×10-5
Mesopic 1
0.625
2.0×10-5
169.9×10-5
178.6×10-5
199.0×10-5
147.3×10-5
Mesopic 2
0.980
271.9×10-5
276.6×10-5
319.8×10-5
235.6×10-5
Mesopic 3
1.393
391.9×10-5
389.0×10-5
462.0×10-5
338.8×10-5
Mesopic 4
1.930
547.9×10-5
534.5×10-5
650.1×10-5
474.3×10-5
Photopic
5.386
1587×10-5
1460.0×10-5
1890×10-5
1355.0×10-5
Table S4. Minimum power conversion efficiency of the QD-WLEDs required for consuming less
electrical power than the conventional sources CWFL, HPS, and MH while generating the same
mesopic luminance indicated in Table S3.
Scotopic
CWFL
21%
HPS
13%
MH
16%
Mesopic 1
24%
26%
18%
Mesopic 2
24%
26%
18%
Mesopic 3
24%
27%
18%
Mesopic 4
24%
28%
18%
Photopic
24%
29%
17%
S4
Table S5. Average and standard deviations of peak emission wavelengths (μ(λ) and σ(λ),
respectively) of the spectra passing the thresholds for all color components for the corresponding
mesopic road lighting standards and vision regimes. The acronyms b, g, y, and r stand for the blue,
green, yellow, and red, respectively.
μ(λ) in nm
σ(λ) in nm
b
g
y
r
b
g
y
r
Scotopic
457.6
512.7
560.6
613.8
5.71
9.20
11.3
4.88
Mesopic 1
460.3
528.9
563.7
610.0
1.93
1.88
2.05
1.06
Mesopic 2
459.4
527.3
561.4
610.4
2.78
9.93
12.9
1.97
Mesopic 3
459.5
528.7
560.3
610.4
2.61
10.4
12.6
1.97
Mesopic 4
459.5
528.1
562.1
611.0
2.61
9.82
14.1
3.02
Photopic
459.8
529.8
564.4
612.3
2.45
8.64
15.3
4.23
Table S6. Average and standard deviations of relative amplitudes (μ(α) and σ(α), respectively) of the
spectra passing the thresholds for all color components for the corresponding road lighting standards
and vision regimes. The acronyms b, g, y, and r stand for the blue, green, yellow, and red, respectively.
μ(α) /1000
y
r
b
σ(α) /1000
g
y
r
199.7
313.3
34.5
39.6
38.0
26.9
244.2
134.2
448.7
36.9
79.9
90.3
61.7
158.5
234.6
144.4
462.8
30.3
82.5
93.3
58.2
Mesopic 3
153.6
243.2
129.9
473.5
25.9
83.9
101.1
52.3
Mesopic 4
146.9
237.5
147.9
467.9
25.3
78.8
92.6
57.8
Photopic
138.4
240.3
151.1
470.3
21.9
72.0
91.6
48.0
b
g
Scotopic
245.6
241.5
Mesopic 1
173.1
Mesopic 2
S5
Table S7. Average and standard deviations of full-width at half maxima (μ(Δλ) and σ(Δλ),
respectively) of the spectra passing the thresholds for all color components for the corresponding road
lighting standards and vision regimes. The acronyms b, g, y, and r stand for the blue, green, yellow,
and red, respectively.
b
μ(Δλ) in nm
g
y
r
b
σ(Δλ) in nm
g
y
r
Scotopic
34.2
36.9
37.6
35.9
4.86
5.40
5.53
5.09
Mesopic 1
37.5
39.3
37.8
33.9
6.17
5.52
5.52
3.32
Mesopic 2
38.7
39.2
37.4
34.1
5.93
5.45
5.84
3.44
Mesopic 3
38.7
39.9
37.2
35.7
5.17
5.53
5.78
4.02
Mesopic 4
38.2
39.0
37.0
36.2
5.10
5.50
5.86
4.61
Photopic
37.7
38.9
36.7
36.1
5.10
5.59
5.61
5.05
4 Synthesis of core/graded-shell CdSe/CdSeS/ZnS quantum dots
For a typical synthesis, 1 mmol CdO, 2mmol Zn(acetate)2, 5 ml of OA and 25 ml of 1-ODE
were loaded into a 50-ml three-neck flask. Then, the flask was degassed for nearly 2 hours at
100⁰C under vigorous stirring to remove the oxygen, water and other residues. Subsequently,
the temperature was raised to 310⁰C under argon flow and a solution of TOPSe was injected.
The TOPSe solution was prepared via dissolution of 0.2mmol of Se powder in 0.2ml of TOP
and 0.8 ml of ODE mixture. After nearly 1 min, 0.3 ml of DDT dissolved in 0.8 ml of 1-ODE
was injected dropwise. After 20 minutes of growth, a solution containing 2 mmol of S
dissolved in 1 ml of TOP was injected. Then, the quantum dots were allowed to grow for
another 10 minutes to complete the synthesis. The mixture was cooled down to room
temperature and precipitated with hexane/acetone mixture twice. Then, the resulting quantum
dots were dissolved in hexane and used for further experiments.
S6
5 Synthesis of core/shell quantum dots
New generation CdSe/CdS core/shell CQDs are synthesized in two steps. Firstly, CdSe cores
are synthesized. In the CdSe core synthesis, cadmium myristate and selenium dioxide are used
as cadmium precursor and selenium precursor, respectively. They are dissolved in octadecene
and evacuated at room temperature for 10-15 minutes. After evacuating the solution, the
solution is heated to 240 ⁰C within 10 min. When the temperature is reached 220 ⁰C – 240 ⁰C,
the nucleation of CdSe cores are started and observed with the change of solution colour to
yellowish. Then, the temperature of the solution is kept at 240 ⁰C for the growth of CdSe
cores until the desired size of CdSe cores is reached. After that, the reaction is stopped by
decreasing the temperature. Finally, as-synthesized CdSe cores are precipitated by using
acetone and dissolve in hexane. For the coating of CdS shell, certain amount of CdSe cores
(100 nmol) dissolved in hexane is loaded to four-neck flask containing 3 mL octadecene and 3
mL oleylamine. Then, the solution is evacuated at around 100 ⁰C remove hexane and any
other organic residuals. After that, the temperature of the reaction solution is set to 300 ⁰C for
the coating of CdS shell under argon atmosphere. When the temperature is reached around
240 ⁰C, injection of calculated amount of cadmium precursor (cadmium oleate diluted in
octadecene) and sulphur precursor (octanethiol diluted in octadecene) is started with a rate of
3mL/min. After complete injection of shell precursors within two hours at 300 ⁰C, the reaction
is stopped with decreasing the temperature. As-synthesized CdSe/CdS core/shell CQDs are
precipitated with acetone and dispersed in hexane.
S7