In market we find same spec LED fixtures with a huge variations on pricing. Especially for Industrial LED lighting its a huge challenge ensure that you selected the right product. This blog will help you in evaluation of LED fixtures technically.
www.leizur.co.uk are experts in selecting right product for your LED lighting application, Interior, Exterior, Industrial or Explosion proof. With lighting designs and ROI calculations Leizur Ltd helps clients to achieve 100% assurance on product selection and technical compliances prior product procurement.
LED PERFORMANCE
A. System Efficacy
The efficacy of a LED fixture is the cumulative efficiency of its LEDs, heat sink, driver and optics. The system level efficacy of a LED luminaire is typically 25-30% less than the LED component due to losses from thermal, electrical and optical efficiency.
For example, the LED component efficacy may be in the range of 140 – 150 lumens per watt, but after efficiency losses, the total system efficacy may measure in the range of 100-105 lumens/watt. Please ensure the efficacy mentioned in the product datasheet is of luminaire not the LED component. Speak with us (mail@leizur.co.uk) if you have more queries on this.
B. Lumens vs Footcandles
HID, incandescent, fluorescent and other traditional forms of lighting provide omnidirectional light. LEDs provide
directional light which focuses the light to the target area. Lumen is the amount of light output in a specific angle from a light source. A footcandle is the amount of light output from a light source in a square foot area.
A LED light fixture that is equivalent to a HID light fixture will have a lower lumen output than the HID fixture. This is because of light lost from the HID fixture’s omnidirectional light pattern. To ensure that the proper LED light fixture is selected to maintain adequate footcandles in the work area, some LED light fixture manufacturers provide lighting layout services. These services provide renderings and reports of the expected performance of the LED light fixture in the application.
This analysis is useful when site upgrades are implemented from HID to LED fixtures. For a given area, layouts for LED versus HID often times result in less required fixtures with equal footcandle performance due to the LED luminaire’s directional light pattern. (Contact mail@leizur.co.uk for free Relux lighting simulations for LED upgrade projects.)
III. LED SELECTION ATTRIBUTES
A. Rated vs Economic Life
Economic life is the period of operation before failure. This is based upon the LED component and the light fixture’s driver lifetime. The fixture’s lifetime is dependent upon the weaker of the two components, which is the driver. Rated Life is defined as the maintenance free life of an LED fixture under worst case operating conditions during an always on, constant temperature environment. LED lifetime is measured using lumen depreciation curves. When an LED is manufactured, it must be entered into a series of tests at 3,000, 6,000, and 10,000 hours. These tests are executed by a 3rd party to measure performance at multiple temperatures and amperages. After each testing interval, the manufacturer receives a TM-21 test report. This test report provides the specific details regarding the LED’s performance. The TM-21 report uses specific calculations to define the Lumen Maintenance report (LM-80). After the LED has been selected for the light fixture, its performance is measured to validate light output, LED junction temperature, and case temperature. The LM-80 data is used with this data to define the L70 lifetime of the LED. L70 is the number of hours after which a LED’s light output depreciates by 30%. To ensure long life, LED fixtures must be constructed with robust and durable heat sinks that allow maximum heat transfer from the LEDs to the ambient environment. Inshort, it is mandatory to review the L70 data and LM-80 report to ensure the life time of fixtures.
C. Electrical Performance
Drivers or power supplies are utilized to energize LEDs. These devices step down incoming voltage and convert it from AC
to DC. Drivers can be constant voltage or constant current output. LED fixtures designed to use constant current output isolate the LED fixture from fluctuations in current and voltage. This can result in reliable operation over time. Many drivers have
surge protection which eliminates the need for additional protection devices (i.e. fuses). Redundancy in drivers can also ensure
reliable operation over time. Multiple drivers connected to multiple LED circuits ensure that a light fixture will have a string of
LEDs illuminated in the event any one of the drivers fails. Within a wide input voltage range of 120-480VAC, LED drivers have very high power factors (PF) and low total harmonic
distortion (THD). The most efficient power supplies will perform with a PF above 99% and a THD below 10%. These
performance characteristics display how efficiently power supplies minimize interference to other electrical equipment and
reduce the load on an electrical system.
D. Energy Efficiency
Industrial manufacturers globally are experiencing higher costs of electricity, which has inspired engineering and
maintenance staffs to identify energy saving solutions. With the large installed base of HID fixtures around the world, LED
light fixtures can provide significant energy savings.
For example, a 400W HPS industrial floodlight that is installed in a processing plant requires 464 input watts of power.
With light fixtures that are spaced 30 feet apart inside a 1200 square foot area, the total fixture requirement would be 40
fixtures. At 464 watts per fixture, that creates an energy requirement of 18.6 kilo-watts (kW) per area.
A LED light fixture that provides the same light output as the 400W HPS floodlight requires 112 input watts of power. By
upgrading the 40 light fixtures in the area to the LED light fixture, the energy requirement is 4.4kW per area. The LED light
fixture delivers a 76% energy savings in addition to four times longer life compared to HPS. This enhances safety through
reduced electrical energy load requirements. The reduction in total wattage and amperage due to the more energy efficient LED
fixtures can result in lower requirements for circuit breakers, transformers and wire conductors in a process facility.
E. Light Quality
Due to the directional nature of LEDs, custom optics should be incorporated into the construction of the LED light fixture.
Optics enables more uniform light distribution, improved coverage and minimal light loss in the work area. This enables the
industrial facility to maximize application spacing and minimize the number of light fixtures required to safely illuminate the
work area. Some examples of common optics utilized in industrial locations are:
1) Type I – Long and narrow beam distribution for applications such as aisles, catwalks, ramps, tunnels, long
passageways, conveyer belts, loading docks etc.
2) Type III – Semicircular kidney shaped beam pattern for Narrow crosswalks or passages with wall fixtures, Tunnels with
wall mount, Wall stanchion mount with 180° forward throw.
3) Type V – Circular beam pattern for Pendant, ceiling or stanchion mount overhead building, Processing mills, industrial
plants, large buildings, warehouses etc.
Color Rendering – Per the Illuminating Engineering Society of North America (IESNA) [5]…measure of the degree of color
shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated
by a reference source, of comparable color temperature… Color rendering indicates the degree to which a light source shows
the true colors of the objects it illuminates. It is expressed in terms of a color-rendering index (CRI) on a scale of 0–100. The
higher the CRI the truer people and objects look [6]. HPS light fixtures typically have a very low rating, with a CRI = 22. For
example, in a maintenance area where the worker must use a black, white, and green wire, the low CRI will prevent the ability
to discern between the black and the green wires and could result in improper installation.
LEDs are manufactured and tested in accordance with American National Standards Institute (ANSI) standard C78.377-
2008 [7] that specifically defines color temperature and color rendering. This process is called binning. Therefore, if a
processing area was replaced with a LED light fixture with a CRI of 70; it would provide the workers three times more
accurate color for quality checks, reading gauge measurements, and performing precision tasks. Improved color rendering
provides a safer work environment and improves workers’ quality of life [8].
F. Durability and Reliability
A key factor in a LED light fixture’s safety and lifetime is Ingress Protection (IP). Per ANSI/IEC Standard 60529 [9], IP is
the degree of protection an enclosure has against access to hazardous parts inside the enclosure, water ingress, and solid foreign
objects ingress.
LED light fixtures are commercially available that have an ingress protection level of IP66 which is zero foreign object ingress, and zero water ingress from powerful water jets. A light fixture that has an ingress protection rating lower than IP66 does not have the same performance characteristics. Robust light fixture construction that prevents failures in areas of flying debris, high pressure wash down areas is critical to safety and performance. Fig. 2 and Fig. 3 show examples of harsh industrial
applications for LEDs.
