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Whats behind the improved warranty terms ?

IMPROVED WARRANTY TERMS – HOW ARE SUCH IMPROVEMENTS POSSIBLE?

From January 2022 the standard warranty on NVC products has been changed:

 

Product range

Old warranty

New warranty

Contractor

5 years unlimited hours

7 years unlimited hours

Core

5 years 20,000 hours

5 years unlimited hours

 

These are big changes – how are they possible?

THE 5 MINUTE ANSWER

The advantage of being a manufacturer. We are a manufacturer, so we have end-to-end control of our product design, manufacturing processes and supply chains. This gives us the ability to drive quality and reliability constantly upwards.

“Not cheaper but better” is our ethos. The unit cost of LEDs has fallen, but we have taken that as an opportunity to raise the quality of the LEDs we use, rather than focus only on the price we pay.

Higher efficiency = Less heat = Greater reliability. Wherever we can we are choosing to use more and more efficient LEDs. Higher efficiency means that less energy is converted to heat, so the LEDs and their drivers stay cooler and last longer.

We are continually improving luminaire design to enhance reliability

  • For example, we assemble LED panels differently from just a few years ago. The design and materials we use now accommodate better the natural expansion and contraction that occurs in daily use. This means that the PCBs are not distorted and the thermal path that ensures the LEDs stay cool functions as well after 5 years as when new.
  • We have changed the way we bond our LEDs to their circuit boards. This gives better thermal management in our downlights, battens and amenity bulkheads, so failures due to over-heating are now almost unheard of in our product range.

 We have improved our LED drivers. In several market areas we have taken the decision to upgrade the capacitors we use in our drivers. These can now withstand higher temperatures for longer, so reliability is improved.

 We are providing better product data and application information. We are providing more comprehensive and accurate product data than ever before. Catalogue pages, data sheets, photometric data etc – by providing these we help our clients to make the right choices and select the most suitable products for each application.

IMPROVED WARRANTY TERMS – THE TECHNICAL DETAILS
There is a double-win for our customers in the changes we have announced.

  • The warranty terms have improved to 7 years unlimited hours (Contractor products) or 5 years unlimited hours (Core products).

and

  • The “bar” of acceptable product performance has been raised. Our definition of acceptable performance has been standardized and raised. Our LEDs are now warranted to deliver L80, 100,000 hours (for Contractor products) and L70, 50,000 hours (for Core products).

BACKGROUND

In 2013 most of our sales were of fluorescent lighting and we were still launching new fluorescent products as recently as 2014. In those early days the warranty on many LED drivers was just 1 year.

Since then, all fluorescent and HID fittings have been discontinued and replaced with LEDs. In the process, new industries have been created, new manufacturers have come (and gone), new processes have been pioneered, refined, perfected – and in a few cases rejected. At all stages, NVC has been close to the forefront in light fitting design, component selection and manufacturing process development, always striving to make changes that would increase product performance and reliability.

NVC RELIABILITY PERFORMANCE

The result of our focus on product reliability is clear in this chart covering the last 4 years.

Faulty Products Returned Graph
SPECIFICALLY, WHAT HAVE WE DONE TO IMPROVE PRODUCT RELIABILITY?

It would take many pages to list the hundreds of small changes that have been made, but here are a few:

REDUCING THE RATE OF OUTRIGHT LED FAILURE

Here are three specific changes that we have embraced that have reduced the incidence of the outright failure of individual LEDs.

  • Crystalline substrates. LEDs contain crystals that are deposited (by a process called epitaxial deposition) on a crystalline wafer substrate. The desired qualities of the substrate are high thermal conductivity, high electrical resistance and a consistent crystalline structure. Traditionally, sapphire was used as the substrate, followed by aluminium oxide (Al₂O₃). The latest material to be used is aluminium nitride (AlN), which has even better thermal, electrical and physical characteristics than aluminium oxide.
  • Lead frame materials. The lead frame is a component in an LED and the material used for these has changed in recent years, yielding ever increased performance and reliability. Polyphthalamide (PPA) has been overtaken by polycyclohexylene-dimethylene terephthalates (PCT), but the latest, and best performing materials are the epoxy moulding compounds (EMCs).
  • Flip-chips. A flip-chip is a recent development in LED design that eliminates the wire bonds. The wire bonds are tiny metal wires (often made of gold) that connect the LED to the lead frame. A flip-chip inverts part of the LED so that connection is made with solder bumps (which are inherently reliable) rather than with fragile wire bonds.

Not all LED manufacturers have embraced these changes at the same rate. By choosing LEDs made in the most advanced facilities we are driving quality and reliability upwards at a rate faster than many of our competitors.

REDUCING THE RATE OF LUMEN DEPRECIATION

More often, LEDs don’t fail completely, but their lumen output and efficiency decline gradually over time. In an extreme case, declining output and efficiency would be exhibited in the failure of a group of LEDs to achieve their L80/L70 and 100,000 / 50,000 hours specifications.

Here too we are choosing to work with the chip manufacturers leading our industry in improving through-life performance. These are some of the recent changes we have made with them:

  • Phosphors. The LEDs we use in the lighting industry generate blue light (450-460nm) that is converted to white light by a layer of phosphor chemicals. All phosphors exhibit a property called thermal quenching (TQ), in which light emission drops as temperature rises. Obviously, keeping LEDs cool helps to prevent the effect of TQ becoming significant, but recent advances in chemistry are producing phosphors with reduced TQ, or at least, phosphors in which TQ is confined to higher temperatures.

Older phosphors with high rates of TQ suffer a spiraling fall in efficiency as they age. Their power consumption (watts) remains constant, but the proportion of that power radiated as light (their radiated power) declines and the proportion emitted as heat increases. With increased heat generated in the LED, their temperature rises, TQ increases, and the cycle starts again.

This effect amplifies the natural lumen depreciation measured in an LM-80 test

  • Efficiency = reliability. Lower rates of TQ mean that more of the watts consumed are used to generate light, rather than heat. As efficiencies increase, fewer watts are lost as heat, so LEDs remain cooler and less afflicted by the high temperatures that can cause them to fail. With ever higher efficiencies the effect of thermal quenching becomes less significant.

For example:

  • In 2014 the GREENLAND LED non-corrosive delivered 105 luminaire lumens per circuit watt. The latest version (launched in 2018) delivers up to 140 l.lm/c.W – an improvement of 33%.
  • In 2013 the PORTLAND amenity bulkhead delivered 69 l.lm/c.W. The same product in 2019 delivered 88 l.lm/c.W – an improvement of 27.5%

More light from fewer watts means less heat is being generated, so the whole installation can stay cooler,  and therefore operates more reliably.

NOT CHEAPER BUT BETTER LEDs

All LED chip manufacturing processes produce a spectrum of quality and performance. A small proportion of very high and very low quality and the great majority of production in between. As manufacturing processes have improved the entire spectrum has improved in quality while prices have declined.

Our response to this could have been to keep the quality of the chips we are using the same and just pay less for them – improving our margins in the process. However, that’s not our ethos. Instead, we have decided to pay about the same and obtain higher quality components.

Higher quality chips deliver longer life and lower levels of lumen depreciation. Our products have not become cheaper, but they are now better performing and more reliable and therefore represent better value than ever.

OUR LED FITTING DESIGN IS GETTING BETTER AND BETTER

For example, the design of our side-lit panels has evolved in several ways to improve reliability: 

  • Heat dissipation. The LEDs are joined to the aluminium frame with a double-sided, thermally conductive, adhesive tape. The tapes have evolved and are now more thermally conductive than before. In addition, the adhesives used perform better now at higher temperatures and for a longer duration. Together, these changes mean that the LEDs are kept closer to their optimum operating temperature for longer.
  • Light Guide Plate (LGP) materials. Some of our earlier panels used a UV stable polystyrene. Even with added UV stabilizers it is difficult to prevent a PS LGP yellowing after about 5 years of use. All our LGPs now use an acrylic (PMMA) LGP which is not prone to yellowing, even after 7+ years of use.
  • Light Guide Plate (LGP) dimensions. Even though made of plastic (PMMA), the LGP expands when it gets warm – either in summer, or through prolonged use. Expansion causes a problem if it puts pressure on the aluminium frame that holds the LEDs. The LEDs can be crushed, and the thermally conductive tape can be stretched, reducing its effectiveness. All our LGPs are designed so that they have space to expand and contract without putting any stress on the aluminium frame and the LEDs.

LED DRIVERS ARE IMPROVING

Of all the components in a lighting system the one that is most likely to fail is the driver. Drivers are complex (often composed of over 100 individual components) and sensitive to temperature, electrical fluctuations and mechanical shock.

Of all the components in a driver the capacitors are the most likely to fail. Getting the right capacitors is therefore key to the reliability of an entire lighting system.

Capacitors

Capacitors are used at several points in a driver circuit. Their essential function is to store an electrical charge for use later – for example, to absorb the short pulses of electrical energy that cause flicker and release them milliseconds later to deliver a smooth, flicker-free performance.

Capacitor selection for high reliability drivers

When the drivers for the GREENLAND product range, for example, were being specified it was known that these fittings would often be used in industrial applications with high ambient temperatures. Rather than use standard aluminium oxide/ethylene glycol capacitors the decision was made (at an additional cost) to use organic tantalum capacitors to ensure the driver would be suitable in these conditions.

This is another example of the advantages NVC has. Close control of our supply chain (Arcata, which makes the drivers for the GREENLAND is a subsidiary of NVC International) and detailed knowledge of the technologies that determine product reliability and performance, have practical benefits that we can share with our customers.

STANDARDS AND ACCREDITATIONS

ISO9001, LIA membership and FORS accreditation all help us to maintain high levels of operational consistency and efficiency. Over time, all the small improvements made in office procedures, warehouse operations and product design contribute to the elimination of errors and raising of quality.

For the technies

 All you ever wanted to know about capacitor design and selection for LED drivers

 

This is a summary of the technical considerations that went into the selection of the capacitors to use in the driver for our GREENLAND IP65 industrial fitting

 

There are many designs of capacitors but the most popular for power supplies and LED drivers are comprised of small aluminium plates, an insulating layer of aluminium oxide and a fluid electrolyte, typically ethylene glycol (CHOH). However, these are not always the most suitable, especially in high temperature applications such as LED drivers for industrial fittings.

 

      Aluminium v Tantalum as the plate material. Aluminium is one of a small group of metals called the “valve metals” – the others include tantalum, zirconium and titanium. These all have oxides that are natural insulators and the aluminium oxide layer that forms on the surface of the aluminium plate has an insulating function essential to the operation of a capacitor.
 

However, aluminium oxide is not very stable above 85ºC. At a wider range of temperatures (-50ºC up to about 155ºC) tantalum, with a layer of tantalum pentoxide as the insulator, offers a superior performance and excellent long-life characteristics.

 

     Ethylene glycol v Organic compounds as electrolytes. Capacitors require an electrolyte and this is usually a gel or fluid. The most used is ethylene glycol, but this has inherent problems in higher temperature applications:

 

  • Ethylene glycol electrolytes contain up to 20% water. Over time, this can dry out, at which point the capacitor fails completely. Therefore, temperature control inside the driver is critical. As a rule-of-thumb, for every 10ºC temperature rise the life of an aluminium plate, ethylene glycol capacitor is halved.
  • Temperature rise can cause increased internal pressure in the capacitor. This can lead to cracks, leaks and premature failure.
  • Temperature rise can be caused by ripple current elsewhere in the circuit. While capacitors are present to suppress ripple, the amount of ripple determines how much work the capacitor has to do. More work = lower efficiency = more heat = shorter life. So, good circuit design (that reduces ripple) helps to prolong capacitor life.

 An alternative to ethylene glycol is one of the organic electrolytes, such as dimethylformamide (DMF) or dimethylacetamide (DMA). These are suitable for wider temperature ranges and have better long-life properties than ethylene glycol.

 On the basis of these considerations we decided to use organic tantalum capacitor and the reliability of the GREENLAND
driver has been exemplary.