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Understanding LED luminaire lifetime and reliability

LED luminaires are getting cheaper but they’re not cheap so a long life is required, hence the 5 year guarantee.

I last wrote about LM80 TM21 and the life of the LED and what it means in terms of the life of a luminaire.  Whilst the LED life is important there are other factors which need consideration.  The LED is probably the most reliable part.

A luminaire requires 2 parts, besides the LED; a housing and a power supply (driver).  Both of which will affect the overall expected life from the luminaire.

The driver, even more than the LED, doesn’t like heat.  The average for premature failure of a driver is around 5/1000, (0.005%), within 5 years, meaning you can reasonably expect several of your fittings to go wrong and need repair or replacement.  That’s assuming the driver is working at a 50 degree C max case temperature.  If the case temperature gets higher the life of the driver goes down.  Reduce the case temperature by 10 degrees C and you will double the life of the driver.

The housing, apart from providing the aesthetics, is required to remove the heat from both the driver and LED, which is why you often see lots of fins on many designs.  The larger the surface area; the greater the degree of cooling.

So, how does that knowledge help?

Allowing that in many corridors the ambient temperature may be 35 degrees C or more it should be appreciated that the temperature inside the luminaire will be considerably hotter, perhaps as much as 15 to 20 degrees hotter.  That makes the temperature inside the fitting – where the driver is – well over 50 degrees and above the maximum case temperature for the driver.  Care should be taken when a luminaire manufacturer quotes an ambient of 40degs – the internal temp could be well in excess of this and well in excess of the driver operating conditions thus reducing the life.  If the internal temperature is 60 degrees C the life of the driver/luminaire may be as little as 2.5 years.

Most lights now come with a 5 year guarantee so if they go wrong they should be replaced but it will still be very disruptive.

Contact us if you’d like to learn about how good design will help reduce premature failures.

LM80 TM21 – LED luminaire lifetime predictions

I mentioned previously that I’d expand on the LM80/TM21 LED theme and what it means in relation to a luminaire life.  The short answer is…absolutely nothing!  LM80 and TM21 refer, only, to the predicted lifetime of LEDs and COBs.  How the LEDs are mounted, cooled and driven are the key factors affecting luminaire life.

Having said it means nothing, that’s not totally true.  What the data is intended for is to provide a luminaire manufacturer with a way to directly compare LEDs/COBs allowing for the best choice of component to achieve a good luminaire life.

So, what does it mean, in simple terms?

IES LM80-80-2008 “Measuring Lumen Maintenance of LED Light Sources”  is the industry standard method for testing LEDs to determine lumen depreciation over time and is carried out over a 6000- 10000 hour period.  At 1000 hour intervals the luminous flux is taken.  As a typical example (CREE, because we use them) let’s say the depreciation is 3%. That means a 97% maintenance of light output. (and, perhaps, at 10000 hours, 6% depreciation or 94% maintenance) Historically that was it and LED manufacturers could draw their own curve through the test points and boldly quote a 50000 hour lumen maintenance of 70% (L70) output while others would quote 90% (L90).   – Before TM21 came along, there was no agreed standard as to how to predict the end of useful life. This was not helpful for us as luminaire manufacturers or you as customers.

IES TM-21-2011 “Projecting Long Term Lumen Maintenance of LED Light Sources” recommends a method to use the LM80 data to predict the lumen maintenance of an LED.  Basically, an exponential curve is drawn between the 1000 hour test points on a graph plotting lumen maintenance from 70% against a time line of up to 100,000 hours.

This could well give a calculated figure of L70 = 50000 hours

from CREE X-lamp lumen maintenance

However, it is also stipulated in TM21 that the maximum life that may be quoted is 6x the actual test duration. So, if the test duration is 6000 hours the maximum life that can be quote is 36000 hours and would be quoted

L70 (6K) >36000 hours if 6000 hours of testing have been carried out or L70 (10K )>60,000 hours if 10000 hours of testing has been done.

It’s obviously more complicated than this and the tests are actually carried out at 3 different LED case temperatures; 55deg C, 85deg C and a manufacturer selected temperature.  (The meaningful one is 85deg C as this represents practical conditions).

Don’t forget,this is just the LED in lab conditions with controlled cooling and drive current and doesn’t take account of ambient temperatures or power supply life time.

Beware, therefore, what is quoted as a luminaire life.  I’ve seen lifetimes of >100,000 hours to L90 at 25deg C quoted in big type on luminaire datasheets and, in small print, this is with a junction temp Tj  and is the LED manufacturers data. Rather misleading but looks good on the spec sheet.

Earlsmann uses the CREE COB CXA 2530 or 2540. TM21 predictions for these is L90 (6k) >36,300 hours with Tc 105deg and 808mA drive current.  We optimise for a lower case temp of 85deg C. which can only improve the life expectancy.

Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI)

There are two parameters which define the colour of LED light. – colour temperature and colour rendering.

Colour temperature is the perceived colour of the light source.  It is compared with a glowing black body source.  When heated to around 3000K it will glow a warm yellow (think about a 40 watt filament lamp).  When heated to 4000K you get whiter (neutral white) and when heated to 5-7000K you get a bluey white (daylight or cool white).

Warm white is most useful in domestic environments and tends to provide a “homely” feel.  Neutral white is more suited to the office environment as it is slightly brighter than warm white and easier to see by.  Cool white provides the most light for a given amount of power but may appear harsher so but is ideal where good visibility is required such as a gym or car park.

Colour rendering is the ability of the light source to allow colours to be seen accurately and is not directly related to colour temperature.

White light is made from a mixture of colours.  A white LED has a blue source with a yellow phosphor overlay which emits white light when illuminated by the blue source.  Needless to say, the colour rendering may not be great.  Reds will appear purple and oranges rather muddy.  

This is because there is no red within the light source to reflect from the red surface.

In simple terms, the solution is the addition of red phosphors to the yellow overlay.  This provides the red to reflect from the red surface and give a good colour rendering.  It would be desirable if this could be added to all LED coatings but, as always, the issue is cost.  Red phosphors are significantly more expensive than yellow so the cost of the LED goes up.

Does it matter?  In many cases no, but it may have safety implications.

For example, old low pressure sodium (LPS) street lights have a colour rendering index of 20 – pretty poor.  They may be bright but a red car will appear black and may simply be invisible at night.

A moderate to good colour rendering of 70-80 is almost certainly adequate.  The fact that a royal blue shirt may appear simply as dark blue probably isn’t important.  It’s also reasonable for security cameras as it will provide good contrast.

A high colour rendering of 90 or more is probably only required if comparing absolute colours, perhaps in paint or fabric manufacture or in retail.  With a really high colour rendering oranges will look really orange and may sell better than your competitors and you can match a shirt and tie exactly so they will look the same in daylight. (although it is still wise to ask the lady in your life).

So, it’s a choice between budget and application.  You could pay 15-20% more for a high colour rendering so it’s worth asking the question…is it necessary?

At Earlsmann we use CREE LEDs for most of our products.  These are available from 2700K to 6500K and with a CRI up to 95 so we can accommodate most requirements

Cree Announces Next-Generation XP LED Delivering 200 Lumens Per Watt

If you missed the recent announcement from CREE about their latest product release then it's worth a read now

DURHAM, NC -- Cree, Inc. (Nasdaq: CREE) introduces the XLamp® XP-L LED, the first commercially available single-die LED to achieve breakthrough efficacy of up to 200 lumens per watt (LPW) at 350 mA. Delivering up to 1226 lumens in a 3.45 mm x 3.45 mm package, the game-changing Cree® XLamp XP-L LED enables an immediate performance increase of 50 percent or more as a drop-in upgrade for lighting designs based on Cree’s market-leading XLamp XP-G LEDs. 

Read the whole story here

With a world leading manufacturer like CREE it won't surprise anyone to learn that Earlsmann uses their LEDs, almost exclusively, in our products.   In fact, we actually use their COB (chip on board) 2530 which achieves a very creditable 112lm per system Watt (350mA) in our Lincoln Street light with gull wing lens - this takes account of power supply and lens losses.  For the bare COB, at 800mA, the CREE published figure is around 24lm/W.

It is worth mentioning that CREE characterise their products with a junction temperature of 85 deg.C  Many of their competitors quote their products at a junction temp. of 25 deg C which is quite unachievable unless the ambient temperature is around freezing!   What's more, some lighting manufacturers quote the LED life in their data - a bit misleading, I think, as it can't be achieved. 

More on LED specifying next time...
LM80/TM21 

Indoor Tennis Court Lighting

I’ve recently come across a rather novel way of lighting indoor courts which I think worth sharing as it is very effective and very cost effective.

I was asked to quote to replace the lighting on an indoor tennis court.  Simple enough, but the current arrangement was rather unusual.  It was lit with 4x6ft fluorescent fittings the entire length of the court on both sides located more or less at 6m directly above the doubles side lines. (off the playing area) They were angled at about 30deg from vertical.

One solution is obviously to simply replace the tubes with LED but this would mean rewiring each fitting and cleaning the diffusers.

I considered a different approach and modelled the court with our Turin 600x600 suspended ceiling panel and was amazed at the result.

Good overall illumination and uniformity, minimal glare and, since these panels are solid, unlike the fluorescent fittings, they are robust and less prone to damage from mis-hit balls.

 Of course it's not just indoor tennis you can light this way.  Bowling greens, squash, badminton - anything where glare would be an issue.

If you have something you need lit - give us the challenge to come up with something different

Daylight Harvesting with Earlsmann LED Lighting

Daylight harvesting is a technique that is becoming popular as a very good way to keep energy usage to a minimum.  Why pay to run your lighting when the sun can provide all the light you need?  How often do you go into an office and discover the lights are on and the sun is blazing outside.  In fact, you may not actually notice the lights are on the sun is so bright!

All you need to do is turn the lights off to make immediate savings but that (almost) never happens.

A good starting point is a motion sensor as they will turn the lights off for you when nobody is about but this has its own problems as it can quite often be much gloomier at desks farthest from the window.  The solution, of course, is daylight harvesting sensors to maintain a constant lux.  These continuously monitor the amount of light falling on the work surface and adjust the light output from the luminaire accordingly to keep it to the required level.  These can be incorporated in the luminaire so those sitting closest to the window where daylight could easily be 700 or 800 lux would have minimal artificial light whilst those sitting with, perhaps, only 100 lux from daylight can have it boosted to 300 lux or more, as desired, by the luminaire.

With modern controls and LED luminaires this is very easy to achieve.  The initial investment in controls is slightly higher than for fittings without but the payback time is similar and the ongoing savings far greater.

Constant Lux with Brighton LED Bay light

In the picture above we used our 120 Watt Brighton LED bay light to achieve around 700 lux

If you’d like to know more, or to discuss your own requirements, please get in touch.

The LED vs Heat

Heat is a real enemy to the LED whether it is a replacement GU10 or a full luminaire so it is a constant battle to achieve a good design to reduce heat whilst achieving a high lumen output.

How often do you see GU10s looking very sorry for themselves?  Looking blue? Looking a bit jaded?  And this can happen after just a few hundreds of hours.

There are a couple of reasons; first, the design/quality of the lamp is simply very poor and it has failed after a short period or second, the lamp has overheated causing premature failure.

It is less likely these days for the lamp to be of poor design as manufacturing techniques have improved and component prices have come down.  You will notice most GU10 lamps have some sort of heatsink – or fins – around the LED and the miniature power supply is built into the end.  In free air this is almost certainly adequate – ensure good circulation and the heat is taken away from the components.  However, the majority of these lamps get used in the popular downlighter which is very effective at preventing good air flow past the fins.  Not surprising, really, as they were designed for halogen lamps with temperatures up to 700deg C with no need for cooling.

These are usually installed in ceilings with next to no airflow, trapped between the ceiling and the floor above and hidden under layers of insulation.  These areas get hotter and hotter, particularly in summer, and can quickly exceed the safe ambient temperature required around the lamp, typically 35degC. Be aware that whilst the ambient air temperature you can measure may be 30deg C, (apparently “safe”) the important ambient around the lamp itself could easily be 30 or 40 degrees higher, well in excess of safe operating limits for the components.  It will be far worse when used in the fire hood often required to meet fire regs.

The solution? Don’t install replacement lamps in luminaires designed for traditional light sources as they can’t keep ventilate but if you do, make sure there is adequate air flow to keep them cool.

Ideally use a complete luminaire designed specifically for LEDs.  These will be designed with LED technology in mind and will achieve much higher efficacies than replacement lamps (>100lm/W compared with 50 or 60lm/W)

Replacement LED 2D lamps

Everyone, it seems, is offering an LED 2D lamp.  They’re great – plug straight into the existing luminaire socket – fit and forget!  They even come complete with sensor options and emergency packs.

But, have you ever stopped to think about the spec. and how they’re used? No? Well here are some things you may wish to consider.

Firstly fitting them – it’s not quite as straight forward as simply removing the CFL type and plug in the new LED version.  More than likely the luminaire will have a high frequency ballast which you need to disconnect and bypass.  Even with a magnetic one, to achieve maximum energy saving, you need to bypass the ballast.  In both cases rewiring of the fitting is needed.

Then there is the emergency pack.  Fluorescent packs do not work with LED lamps so you will need to buy the LED emergency pack and work out how to install it securely adding to the time, and therefore, the cost of replacement.

Then there is the spec.  Most LED replacement lamps are quoted at 12 watts and around 1000lm.  Indeed a huge saving over the fluorescent type but actually not quite enough light. The cool white ones are 1000 lumens but the chances are you’re replacing a warm/neutral white lamp.  You’re probably only getting 800 lumens from these – well short of what is required.

The Earlsmann solution is to replace the complete gear tray – simpler to install – just the Live, Neutral and Earth to connect and the extra permanent Live for the emergency version.  They are rated at 15 watts so use a bit more power but then they give you 1200 lumens which provides a light level far nearer the original fluorescent. They don’t cost any more than the replacement lamp solution and are quicker to fit.

Of course it may not be suitable for every luminaire so you’ll need to ask us.

Earlsmann at Ecobuild 2014 with the ILP

Ecobuild wasn’t an exhibition that had been on our list of priorities until we had a call from the Institution of Lighting Professionals (ILP) inviting us to join them in their “Lightscene” zone.

We agreed, and were really pleased with the result.  Simon did a 15 minute talk on the Wednesday, “ Lux, Lumens and Watts”, inspired by the ILP “Guide to the Specification of LED Lighting Products 2012” to help people make more informed choices about LED lighting.  After all, LED lighting is a significant investment so it’s important to avoid the many pitfalls. (Also read our other blog articles).

We also took the opportunity to show some of our new products and gauge reaction:-

The Lincoln LED streetlight is available from under £150 and will easily replace up to 90W SOX luminaires.  At the price, it may be a much better option for S class areas than simply replacing the lamp.  This was very well received and several requests for further information were made from as far afield as the UK, Belgium, Spain and Kenya.

The Brighton Bay / Dover flood lights have interchangeable reflectors making it possible to change the beam angle to suit specific applications and for change of use of areas within a building.  LED lighting is a major investment so “future proofing” was considered a good idea.

Replaceable LED geartrays for 2D CFL bulkheads are a good alternative to the readily available LED replacement lamp as the driver is separate and better cooled, allowing the light output to better match the traditional lamp.  The standard LED replacement lamp doesn’t quite have the light output to adequately replace CLFs.  What’s more, replacing the complete gear tray is quicker and easier to install than rewiring for the lamp.

We met with many professionals and lighting specifiers so hope to see an increase in business.  The coming months will tell.

ECOBUILD 2014

Earlsmann are exhibiting at ECOBUILD on stand S548 and will be showing several of their new products.

First is the new LINCOLN LED street light which can be used in S class applications, car parks, walkways or public areas.  It has a gull wing beam pattern and has an efficacy up to 120lm/Watt.  Critically, this is the first street light available at under £150 and is made in the UK.

Next is the new corridor light.  This is a stylish bulkhead and is fitted with twin LEDs pointing along the corridor providing maximum uniformity and avoids the usual light-dark-light-dark that are normally associated with these areas.

Third are the new BRIGHTON S high/low bay and DOVER flood.  As your requirements change it may be useful to be able to  change the beam angle on your lighting to suit different mounting heights or a different use for a given area so these come with interchangeable reflectors to allow for this change of use and future proof your investment in LED lighting.

And fourth is the 2D replacement gear tray.  This is an alternative to a simple replacement lamp and is far easier to install.  MOQ of 50 pcs and we’ll need to see a fitting to make sure it fits.

LED lighting has come down in price but is still a significant investment so if you’re interested in learning a bit about how to correctly specify lighting and avoid some costly pitfalls, Simon Thornton will be giving a  presentation at the ILP Lightscene theatre on Wednesday 5^th at midday.  Why not come along?

LED Lighting and the 5 Year Guarantee

Nowadays it is a given that LED luminaires come with a 5 year guarantee.  But what does that mean and do you know if it can be honoured?  It is very easy to offer a 5 year guarantee; everyone is doing it!

If you’re buying your new light from a reputable supplier of branded products I’m sure there won’t be a problem but, with so many smaller businesses offering Far Eastern products at low prices it may pay to check what is covered.

Some suppliers are even offering guarantees up to 7 years (and even 10), and some include batteries on emergency fittings.  These guarantees should be treated with caution and the small print read thoroughly.   The chances are there will be strict limitations on service life and batteries almost certainly won’t last more than 4 years due to their charging duty cycle

LED lights should be considered as the piece of high tech electronic equipment they really are. Would you expect a television set to run 7 years (over 60,000hrs) without turning it off?

To Do

First, the product, check the specification of the light to make sure it really is fit for purpose, particularly with regards to ambient temperature, which can easily be overlooked.  Sometimes the fitting will only have a low ambient operating temperature, 35 degrees, say.  If your ambient is higher, perhaps 40degrees, this will void the warranty.

Is the guarantee for the luminaire only?

Does it include installation?
Is it a return to supplier guarantee?
Is it for the LED only or does it include the driver (power supply)?

LEDs, in the correct conditions, may well last 50k hours (6 years at 24/7 usage) but will the power supply?  The industry average for power supply failure is 7/1000 supplies.  This suggests that several of your fittings may be guaranteed to fail.  Has the supplier/you taken this into account?

Then, check the supplier.  Will they be around in the coming years to support the guarantee? It’s all very well having a 5 year guarantee but if the installer/lighting supplier has closed down, who is going to honour it?

If you'd like to discuss your options with Earlsmann, please get in touch

Lux, Lumens and Watts

There is a lot of confusion regarding Lux, Lumens and Watts which is worth clarifying so that the best luminaire for a given use can be correctly specified.

Asking the right questions
I am often asked if we can supply a luminaire in Watts.  Do you have a 50 Watt flood light?  Do you have a 100 Watt low bay light?  The answer is “Yes” but the question could be put better.

I need 150 lux in my aisle, do you have a light that can do that?  Or - I need 700 lux at working height in my workshop, can I do that?

Lux (lx)
The wattage of the luminaire, or the lumen output, aren’t important to answer the lux level required but are used to indicate how efficient the luminaire is.  Usually the minimum recommended lux level needed (illuminance at the required surface) is specified in health and safety guidelines, by CIBSE or a regulatory body.
For example, the HSE suggests a minimum average illuminance of 50 lux in loading bays. This is to provide adequate light to safely see other users and provide a comfortable light level to do the required task without causing eye strain.

The luminaire light output required to achieve this will depend on several factors – lux level required, mounting height, area to be illuminated and spacing of the luminaires.  Once this information has been established it is possible to work out the light output required from the luminaire to achieve the desired lux level.

Lumens (lm) is the light output from a given luminaire and
Watts is the power required to achieve it.

Once the lumen output has been established is the time to start considering the power (wattage) required and selecting the most suitable luminaire.

Efficacy (lm/W)
Lumens and Watts determine how efficient a luminaire is and is quoted in lumens/Watt.
A good luminaire nowadays will be at least 80lm/W.  The more efficient a luminaire the fewer will be required and the less power used.  Make sure the efficiency quoted refers to the complete luminaire not just the LED.  An inefficient power supply can lead to an inefficient luminaire.

Example
We recently supplied some Brighton High Bay lights to illuminate a production area to 700lx.  It was determined that we could achieve this using our 120 watt luminaire with a system efficacy of 90 lm/W.  We required 42 fittings.  If the efficacy of the luminaire had only been 60lm/W we would have needed to use either 42 x 180 watt luminaires or increased the number of fittings to 60.  Either the cost of the fitting increases significantly or the installation costs would increase.  Another important thing to note is that 50% more power would be required.

If you would like to discuss further please contact us at Earlsmann.

Earlsmann LED lighting updates

We're into the new year and have been busy with a number of updates. 

Within the Lighting Group we have updated all out data sheets for all our interior and exterior LED lighting products to reflect developments with LED lighting components.  A number of new Ledil reflectors have become available with efficiency over 93% allowing greater efficacy of our luminaires. These are used on our Brighton High and Low bay lights, Stafford and Dover flood lights.

The Dover is a completely new product developed in the last few weeks in response to requests for a waterproof bay light.  Already these are being used by Redbridge Council on their Liston Road estate to illuminate  the ground from the apartment tops and at Heathrow to illuminate some of the undercroft.

Ledil have also introduced a new lens - Stella.  This is also 93% efficient and lead to the new Telford 2 LED street light which is also now specified by Redbridge council for their car parks and walkways.