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www.we-online.com ANO003a // 2018-08-01 // RiB 2
Advantages of LED L
ighting in Horticultural
Applications
Application Note
3 Efficiency
The potential efficiency of LEDs
[5]
over traditional lighting sources has long
been recognized
[6]
. This is because of their low losses, generated as heat,
meaning a greater proportion of the electricity goes towards generating
light. Additionally, this means the light source can be placed extremely
close or even within the plant canopy. The efficiency (wall-plug efficiency)
of light sources is usually expressed as the radiant flux (W) per electrical
input power (W) or luminous efficacy, expressed as luminous flux (lm) per
electrical input power (W) but for horticulture, photon efficacy is used
(µmol J
-1
). This is the output of photosynthetic photons (µmol s
-1
) as a
function of the input power (W). As discussed in Section 2, the PPF and
radiant flux will vary greatly between different wavelengths of LED.
Although blue LEDs have higher wall-plug efficiency than red LEDs, the
difference in photon efficacy is much closer (Figure 2).
Figure 2: Comparison of Photon Efficacy and Wall Plug Efficiency of the
WL-SMDC Deep Blue (150 353 DS7 4500) and Hyper Red
(150 353 HS7 4500)
This is further complicated by the efficiency of LEDs being different for
different materials used to generate different wavelengths in addition to
changing as a function of the input current (Figure 3). The most efficient
‘colors’ of LED, based on photon efficacy, are blue and red.
Figure 3: Typical Photon Efficiency (µmol/J) as a Function of Input
Forward Current (mA)
To compare HID and LED light sources directly, the focus is on the
efficiency of the conversion of electrical power to photosynthetic active
photons (Table 1).
Light Source Type
Electrical
Input
(W)
PPF
(µmol s
-1
)
Photon
efficacy
(µmol J
-1
)
High Pressure Sodium
[7]
400 W (Magnetic)
443
416
0.94
1000 W (Magnetic)
1067
1090
1.02
1000 W (Magnetic)
1024
1333
1.30
Ceramic Metal Halide
[7]
315 W (3100 K)
337
491
1.46
315 W (4200 K)
340
468
1.38
Flourescent
[7]
400 W (Induction)
394 374 0.95
60 W
58 48 0.84
Light Emitting Diode (@350 mA)
WL-SMDC Deep Blue
(
150353DS74500
)
1.12 2.31 2.06
WL-SMDC Hyper Red
(
150353HS74500
)
0.84 1.81 2.15
WL-SMTC Moonlight
(
158353030
)
1.12 1.58 1.41
WL-SMTC Daylight
(
158353050
)
1.12 1.69 1.51
Table 1: The Most Efficient ‘Colors’ of LED, Based on Photon Efficacy,
are Blue and Red
The result of this is that the efficiency is highly sensitive to electricity prices
(Figure 4). As the price of electricity increases, the savings of
implementing an LED lighting system become far more significant.
Figure 4: Cost per PPF as a Function of Electricity Prices in High-
Pressure Sodium (Grey), Metal Halide (Blue), Fluorescent (Black) and
LED (Red).
0
0.5
1
1.5
2
2.5
200 mA 400 mA 600 mA 800 mA 1000 mA
Photon Efficacy (µmol·J
-1
)
Forward Current
Blue Red Cool White Neutral White Warm White Green
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.0 0.1 0.2 0.3
0.4
0.5
Cost per Photon Flux (€/mol · s
-1
)
Electricity Price (€/kWh)
Flourescent 400 W (Induction) Flourescent 60 W
HPS 1000 W (Magnetic) HPS 1000 W (Electronic)
CMH 315 W (3100 K)
CMH 315 W (4200 K)
WL-SMDC Deep Blue
WL-SMDC Hyper Red
WL-SMTC Daylight