User Manual

www.we-online.com ANO003a // 2018-08-01 // RiB 4
Advantages of LED L
ighting in Horticultural
Applications
Application Note
5 Lifespan
When operated at appropriate temperatures, i.e. that well below the
maximum operating temperature, LEDs can last for up to 60,000 hours
equating to 9.1, 13.7 and 20.5 years when operated for 18, 12 and 8
hours a day respectively. This is greatly reduced when LEDs operate at
higher temperatures because of ambient temperature or being driven with
higher currents (Figure 7).
Figure 7: Typical Lumen Maintenance of One Type of LED at Different
Operating Temperatures
[13]
. Markers Represent Measured Data and
Lines the extrapolated Lifespan as per IES TM-21. Dashed Lines
Represent Predictions Beyond the Limits of TM-21
The lower the operating temperature, the longer lifespan LEDs have. In
their lifespan, LEDs can drop to around 70 % of their luminous output.
However, this is highly dependent upon operating temperature.
Because of the relatively high investment needed to replace LED fixtures,
it is thought LEDs will be operated to the limit of their lifespan despite the
lower PPF in the end-of-life period (like HID lamps). Replacement of
individual LEDs is prohibitively expensive and impractical in the field.
However, the LED is often not the limiting factor. Power supplies, fans,
and other components (sealings, fixtures, enclosures, etc.) in LED fixtures
can fail well before the LEDs themselves. It is therefore important for any
LED fixture fabricator to ensure the supporting electronics for the LEDs
are designed with reliability in mind, operating well within operating limits
to maximize the lifespan of the fixture to match the lifespan of the LEDs.
Double-ended high-pressure sodium lamps (1000 W) have a life
expectancy of 10,000 to 24,000 hours (based on manufacturer literature),
or 3.7, 5.5 and 8.2 years when used an average of 18, 12 and 8 hours
per day respectively. However, due to the lumen maintenance
performance, it is expected a lamp will be replaced within the first five
years. Replacing the bulb increases maintenance costs, due to labor and
replacing the bulb. Metal halide lamps have a lifespan between 6,000 and
20,000 while fluorescent (T-5 and T-8) a lifespan of 20,000 to 36,000.
Again, due to the lumen maintenance, it is expected that lamps will be
replaced before this maximum is reached. A comparison of the lifespan of
light sources can be seen below (Figure 8).
Figure 8: Comparison of Life Eexpectancy Between Metal halide (MH),
High-Pressure S(HPS), Fluorescent and LED Light Sources.
6 Physical properties and environmental
impact
The small size of LEDs and their fixtures, in combination with their low
operating temperatures, allows them to be positioned in places HID
sources cannot such as intracanopy lighting and means there is no risk of
burn injuries to operators. Their low operating temperature also allows
LED fixtures to be fully or partially encased which can be water and/or
dust resistant. Because of their fabrication, LEDs are significantly more
resistant to shock meaning less risk when handling or transporting lamps
and fixtures. They do not use glass in their fabrication which can be easily
damaged and cause injury. Unlike HID light sources, LEDs are RoHS
compliant, which means they do not contain mercury that necessitates
specialized disposal. In addition, they do not generate UV wavelengths
(unless specifically added) as HID lamps can do if damaged. Because
LEDs can be operated close to the canopy with a smaller emission pattern,
and because they only emit the specific wavelengths used by plants they
produce much less wasted light and therefore reduce energy electricity
use.
50 %
60 %
70 %
80 %
90 %
100 %
0 kh 20 kh
40 kh 60 kh 80 kh 100 kh
Lumen Maintenance
Time
55 °C 85 °C 105 °C
60.000 h
TM-21 limit
L70
TM-21 limit
0 kh 20 kh 40 kh 60 kh 80 kh 100 kh
Lifespan