Regarding 100,000hrs Lumen maintenance claims for LED lighting

December 4, 2018

Regarding 100,000hrs lifespan claims for high bay/high power luminaries-    

 

The majority of Industrial LED lighting products have a lifespan rating of 50,000hrs for what is known as L70 specification.

 

The L70/L90 figure, refers to the percentage of original light output –after the stated lifespan period has passed.

 

This is known as the products lumen maintenance, a 50,000hrs L70 product will lose 30% of its original brightness after 50,000hrs.

 

For example:

 

A site area requires a minimum level of lighting to meet safety requirements as all lighting products progressively have a reduced light output as time goes by all lamps gradually depreciate. The lighting scheme planner must take into account how much light will be delivered after 50,000hrs has passed.

 

As a result, if a room/area requires a lamp which outputs 10,000Lm to meet lighting safety levels for 50,000hrs the planner will select a luminaire with an output of 14,285Lm with a 50,000hr L70 rating – so after 50,000hrs, the onsite light levels are still legally compliant and safe.   

  

Note: If lighting products are not selected this way, the following problem can arise:

 

The site lighting levels were compliant to safety requirements at the time of installation but after 30,000/50,000hrs, the light levels have dropped, and the site end up with insufficient lighting levels this makes the site legally venerable [anyone who has an accident at that time, could make a legal claim against the site].  

 

Claims of 100,000hrs product life span, have little relevance if the lighting product, only outputs 10% of its original brightness after 30,000/50,000hrs and causes a breach of lighting safety laws onsite.

This also results, in the site having to replace the worn out/dim lighting units for new ones at additional cost of labor/new lamps site closure costs. 

 

Can a LED high bay product work for 100,000hrs at L70 specification?   

    

There are two factors which governs this:

 

1. The lifespan of the LED driver [the units power supply] this is governed by the lifespan of the drivers weakest component most commonly the driver’s electrolytic capacitors.

 

The driver’s lifespan will vary – depending on the following aspects:

 

A. The temperature on site- if temperatures are higher than expected, the drivers lifespan can be reduced.

 

B. Power quality – if the mains supply has issues such as dips/interruptions/surges it will place additional electrical stress on the driver’s protection circuitary which may wear out/overstress the driver – causing it to have a reduced lifespan –or fail prematurely.

 

C. The number of times the driver is switched on/off – all drivers have a limit to this [ known as switch on /switch off cycles] if working for 12 hours a day for 365days – 100,000hrs equates to 22 years of on/off switch cycles! 

 

2. LED lifespan – as mentioned, all light sources depreciate over time. An LEDs lumen maintenance depends on the LEDs operating temperature when working in the product.

 

All lighting products have a working temperature range, known as Ta – temperature ambient for example, a rating of -10C to 45C, means the unit is not designed to deliver long term performance -if ran at a constant 50C ambient.

 

If a product has a 50,000hr L70 rating and a Ta of -10C to 45C, it will not deliver the correct light output after 50,000hrs if ran above 45C.   

 

It is important to note, the site’s ambient temperature has to be taken into account – bearing in mind that temperatures at ceiling height [where the lights are] can be greater than found below [sometimes by 10C to 15C or more – depending on the site].  

 

Note: It is possible – that a lighting product could have a greatly extended lifespan- providing the product runs from a clean mains supply [with no issues] and runs constantly at low ambient temperatures.

 

Predicting this, all depends on the design of the individual product and its LED specification- but there are many factors to consider.   

  

Our industrial range has been designed/ tested for worst case scenarios – E.G. if the units rating is 50,000hrs/L70 -10 to 45C, the unit can run constantly at 45C for 50,000hrs and still achieve 70% of its original light level [so the site’s light levels will still be compliant after 50,000hrs] 

 

Be warned-some products on the market, cannot run constantly at their max, Ta rating and deliver 50,000hrs L70 performance – the Max, Ta rating may refer, to the highest temperature the fitting can withstand before failing – not the max, working temperature that allows 50,000hrs /L70 performance. 

 

Q- If a 50,000hrs /L70 [with a max Ta of 45C] lighting product is running well below its’s max, Ta rating – can we predict the lumen depreciation [light loss] after 100,000hrs?

 

As mentioned before, this depends on the individual design of each product – in this case we look at our 150W UFO high bay light as an example:

 

This 150W UFO employs the Phillips Lumiled LED.

 

When the product is running in 25C ambient temperatures – the LEDs maximum temperature is 67.9C.

 

The LED temperature [in the product] is compared with the LED manufacturers lifespan prediction for the LED, this prediction is based on what is known as  an LM80 report –this shows the comparison between the manufacturers lifespan prediction vs actual test data.  Please see Philips Lumiled LM80 data below:

 

LED temp,         L70 time

 

Ts= 105C         >54,000Hrs

Ts= 85C           >54,000Hrs

Ts=55C            >54,000Hrs

 

For Luxeon 30302D  part no, L130xxxx003000W21   CCT=White . If = 165ma. Limited by TM21 rule.

 

As the LED runs at 67.9C at 25C ambient in the 150W UFO- and the max, Ta rating is 45C, we can state that when the 150W UFO runs at 45C ambient – the LED’s temperature is 87.9C. 

  

The LM80 report shows, that the LED will achieve 54,000Hrs /L70 even when running at 105C/165ma!

 

This does not mean the product can run at 62.1C ambient [where the LED would run at 105C] as the LED driver’s temperature limit would be exceeded. 

 

Important note: There are two ways of looking at the LEDs lifespan –LED manufacturers makes a lifespan prediction for the LED – but unless the LED has already been tested for 50,000/100,000hrs there is no absolute proof this will be the case.

 

The lighting industry uses a different system- called TM21 calculus, which works as follows:

 

The LED is measured/tested at 3 different temperatures and is monitored for light depreciation over time.

 

The results are compared with the manufacturer’s prediction- if the data matches the prediction so far, the test house will state the LED is on track to perform as predicted for 6X the elapsed test period – for example, an LED which has been tested for 1,000hrs [and matches the prediction] can have a TM21 prediction of 6,000hrs.  

 

Some lighting manufacturers, state the LED manufacturers predicted lumen maintenance- not the TM21 calculated lumen maintenance [often quoted from a LED data sheet – not based on thermal testing of the actual product].

 

The LM80 report for the Phillips Lumiled is on-going, only 9,000hrs of test time has elapsed – as the test progresses we expect an increase of the L70 hours at 85C. After 30,000hrs of test time we will know more.

 

Please see example of Lumiled lifespan prediction curves at differing LED temperatures on page below.

 

The dotted lines represent the manufacturers LED prediction – the solid lines represent the calculated TM21 prediction so far.

 

We see that LEDs running at 105C do not achieve L70 maintenance after 55,000hrs – but LEDs running at 55C can achieve L60 [60% of original light level] past 100,000hrs.

 

However- if the LED runs 30C warmer, the LED will not achieve L60/100Hrs.This demonstrates, the site ambient temperature can affect the predicted lifespan.

 

 

As the LED runs at 67.9C at 25C ambient in the 150W UFO- and the max, Ta rating is 45C, we can state that when the 150W UFO runs at 45C ambient – the LED’s temperature is 87.9C.

   
The LM80 report shows, that the LED will achieve 54,000Hrs /L70 even when running at 105C/165ma!
This does not mean the product can run at 62.1C ambient [where the LED would run at 105C] as the LED driver’s temperature limit would be exceeded.  

 

Important note: There are two ways of looking at the LEDs lifespan –LED manufacturers makes a lifespan prediction for the LED – but unless the LED has already been tested for 50,000/100,000hrs there is no absolute proof this will be the case.


The lighting industry uses a different system- called TM21 calculus, which works as follows:
The LED is measured/tested at 3 different temperatures and is monitored for light depreciation over time.


The results are compared with the manufacturer’s prediction- if the data matches the prediction so far, the test house will state the LED is on track to perform as predicted for 6X the elapsed test period – for example, an LED which has been tested for 1,000hrs [and matches the prediction] can have a TM21 prediction of 6,000hrs.   


Some lighting manufacturers, state the LED manufacturers predicted lumen maintenance- not the TM21 calculated lumen maintenance [often quoted from a LED data sheet – not based on thermal testing of the actual product].


The LM80 report for the Phillips  Lumiled is on-going, only 9,000hrs of test time has elapsed – as the test progresses we expect an increase of the L70 hours at 85C. After 30,000hrs of test time we will know more.


Please see example of Lumiled lifespan prediction curves at differing LED temperatures on page below.


The dotted lines represent the manufacturers LED prediction – the solid lines represent the calculated TM21 prediction so far.


We see that LEDs running at 105C do not achieve L70 maintenance after 55,000hrs – but LEDs running at 55C can achieve L60 [60% of original light level] past 100,000hrs. 


However- if the LED runs 30C warmer, the LED will not achieve L60/100Hrs.This demonstrates, the site ambient temperature can affect the predicted lifespan.

 

 

LM80 Prediction Chart

 

TM21 is the solid line- manufacturers prediction is the dotted line.

 

Note: Unlike the TM21 calculus -this is only a prediction- this prediction may change/improve as time goes by.

 

Bear in mind, that over 100,000hrs –the lumen maintenance can be affected by the following:

 

1. Miss-judgment of onsite ambient temperatures – or unexpected high ambient, through climate change [this could have a dramatic affect - if the error is compiled over 22 years]

 

2. Sunlight hitting the fittings – creating additional unexpected heat.

 

3. Alterations in the use of the factory – causing additional heat and dust.

 

5. Badly estimated cleaning schedule – leading to build up of dust on luminaires – causing overheating/reduced lumen maintenance.

 

6. Power quality issues – such as dips/interruptions/surges /overvoltage and onsite supply faults.

 

7. If the luminaire uses heatsink paste – it may not have a 100,000hr lifespan.

 

8. The LED driver may not last for 100,000hrs.     

 

TM21 calculus is the industry accepted way of making accurate reasonable lifespan predictions – which also take into account LED tolerance variations [the B value] and other limitations such as driver lifespan.

 

If purchasing a product that promises 100,000hr/L70 performance –we would ask for TM21 proof + thermal test results, and we would also require a warranty that guarantees /covers L70 lumen maintenance when ran at the highest Ta rating.

 

Otherwise it may be just wishful thinking on the supplier’s behalf –based on LED manufacturer’s predictions [but with no hard evidence – such as thermal tests and TM21 calculus]

 

We recently examined a 200W high bay light -which is sold as having a 100,000hrs lifespan. We found it used the same Phillips Lumiled LEDs as our high bay UFO’s. This means the competitor unit had exactly the same lumen calculated depreciation as ours [54,000Hrs /L70].

 

If our UFO ran in a constant ambient temperature of 45C, the LED would run at 87.9C. This would give an LED predicted L60 lifespan of 90,000hrs and a L70 lifespan of 60,000hrs [but this assumes the driver will last as long].

 

The competitor unit may use a different heatsink [running the LED hotter or colder] this would affect its lifespan predictions- this can be assessed, only with product thermal testing and LM80 data. 

  

Note, that LED efficiency is improving all the time – a new product does not use LED from 5 year ago- so the new product use LEDs which have not been tested for 50,000hrs.

 

This means, that most of the new products do not have LM80 report for the LEDs allowing long term TM21 predictions to confirm the manufacturers LED lifespan expectations.

 

So – when we see a product claiming 100,000hrs [with a Ta up to 45C] we know, that the LED has not been tested for 100,000hrs – and the TM21 prediction may only have reached a prediction of around 50,000hrs.

 

This suggests the manufacturer is using wishful thinking, instead of industry proved methods of proof.as well as igno