January 2020 - 50

technically speaking
BY ERIK RUNKLE
LED Fixture Efficacy: A 2020 Update
Light-emitting diodes (LEDs) have come a long way in the
past decade. The prices for LEDs have come down, their output
has greatly increased, and their efficacy (energy efficiency)
has dramatically improved. Back then, we didn't discuss fixture
efficacy and with rare exceptions, the prices were just too high
for large-scale commercial application.
In 2014, we communicated the efficacy of LED fixtures that
were then on the market. This marked the beginning of our use of
the term fixture efficacy, which is the amount of photosynthetic
light emitted (micromoles of photons per second, or
µmol·s-1
(watts, which equals joules per second, or J·s-1
resulting unit is micromoles per joule, or µmol·J-1
) divided by the amount of energy consumed
). The
. The
most efficient LEDs in 2014 were as efficient as the most
efficient conventional lamp, the double-ended 1,000watt
high-pressure sodium (HPS).
In October 2018, the Design Lights Consortium (DLC)
published technical requirements for a horticultural
lighting fixture to become qualified and included in
their Horticultural Lighting Qualified Products List
(QPL). Qualified products are usually eligible for energy
efficiency incentives and rebates from utility companies
throughout the U.S. and Canada. Among the minimum
qualifications are a 5-year warranty, photosynthetic
light maintenance of at least 36,000 hours, and a
minimum efficacy of 1.9 µmol·J-1
.
As we enter 2020, there are already more than 50 LED
Erik Runkle is
professor and
floriculture
Extension specialist
in the department
of horticulture at
Michigan State
University. He can be
reached at runkleer@
msu.edu. Reference
to companies,
commercial products,
or trade names
does not imply
endorsement or bias
against those not
mentioned.
products on the DLC Horticultural Lighting QPL. The spectrum,
amount of emitted light, and efficacy vary widely among
fixtures. Some of the products primarily intended for highintensity
greenhouse lighting applications are listed in Table 1. A
full list of products, including ones primarily for indoor lighting,
as well as additional details, are available on the DLC website
at www.designlights.org/horticultural-lighting. Information
about each fixture was generated by accredited laboratories
and thus is unbiased.
The photosynthetic photon flux refers to the amount of light
emitted per fixture, and for those in Table 1, varies from 766 to
1,636 µmol·s-1
. All of these fixtures include white LEDs. Ones
that emit a low percentage of green light (less than 10%)
indicate that there are relatively few white LEDs per fixture,
and the light emitted will appear pink to us. Those with a
higher green light percentage indicate a higher percentage of
white LEDs per fixture and thus, the light will appear whiter.
While all of the DLC-listed fixtures are more efficient than HPS
fixtures, their efficacy varies considerably, by as much as 50%.
Clearly, there are a lot of differentiators among LED products
for plant applications.
MANUFACTURER
AND MODEL
PHOTOSYNTHETIC
PHOTON FLUX
(µmol·s-1
)
Blue Green Red
California
LightWorks
GHPRO 340
Esttech
EST-LED-GH001
Fluence
VYPR 2p
Greenhouse
Illumitex
HarvestEdge
EDG1S12NLX6
Lumigrow
TopLight Adjustable
Targeted Spectrum
MaxLite
PH-GH600 BPRX
Philips
GP Toplighting
2.1 DR/W LB HO
Sunritek
GX530A
FSG 26 D1
Table 1. Examples of LED products primarily for high-intensity
greenhouse lighting on the DLC Horticultural Lighting Qualified
Products List.
Although LEDs have become much more economically
viable, growers are still encouraged to compare purchase
and operation costs with HPS fixtures, especially for tall
greenhouses, where 1,000-watt double-ended HPSs can be
used. These lamps emit a photosynthetic photon flux of around
1,840 µmol·s-1
and have an efficacy between 1.7 and 1.8
J·s-1. Therefore, it usually takes more than one LED fixture to
match the light output of this 1,000-watt HPS fixture. However,
the most efficient LEDs available now are over 50% more
effective than these HPS fixtures, making LEDs compelling when
electricity prices are high and/or when lighting is needed more
than a few months of the year. The availability of utility rebates
can also sway investment decisions.
784
6
6
88
2.78
1,442
17
7
76
2.33
766
17
40
53
2.35
890
10
21
68
2.61
RADIATION
PERCENTAGE
EFFICACY
(J·s-1
)
839
10
38
52
1.81
1,636
23
42
36
2.50
1,144
16
39
45
1.98
1,281
8
42
40
2.48
50 JANUARY 2020 GPNMAG.COM
http://www.designlights.org/horticultural-lighting http://www.GPNMAG.COM
January 2020

Table of Contents for the Digital Edition of January 2020
