Many product specifiers and light plan engineers, may compare the IES files of similarly constructed high bay lighting products from different manufacturers, and may conclude that the LEDs + Meanwell driver will perform identically in all of these products- with the only perceivable difference being the price and slight differences in efficacy.
Q- Is it possible to discern from IES files / product specification – which units will be the most reliable – and which units could potentially have onsite reliability / fitness for purpose issues later?
A- No, the products may have the same spec, /make of driver and LED – but when it comes to reliability, the following factors can vary -even on designs using the same make of driver and LED:
1. LED redundancy factor- how many LED strings can go faulty [open circuit] without affecting product reliability [some cheaper designs may not have any redundancy built into the LED array]?
2. Management of perishable production materials [such as the heatsink paste] for example: Some pastes may have been stored for too long –or at high ambient temperatures [it may be tempting to use materials past their use-by date to save money] – does the factory inspect/check such materials- what is the paste’s lifespan? – is enough paste being applied? [If the factory starts to economize the use of paste – it can lead to Ta issues]
3. Degree of electrical and thermal headroom for the LEDs. The closer the LEDs are driven to their max, current rating – the more heat they generate [as well as loosing efficiency] – if this is combined with a poorly rated heatsink [with low surface area] the product may pass initial thermal tests [just]– but may fail when running in a dusty environment with close to maximum Ta readings. A good design includes a degree of thermal headroom added to the max, Ta rating.
4. Degree of Ta headroom of the driver- if the driver unit heats up too much, the driver’s lifespan will be reduced- this can happen with bad thermal designs [where the LEDs are heating up the driver] and on units, with a low driver efficiency [where the driver generates more internal heat] – or both [caused by poor matching between load and source]
5. Driver efficiency [again -this could affect the actual Ta rating of the product/lifespan of the driver]
6. Type of LED current start up waveform [which can vary with different models of Meanwell drivers and loads] if attention is not paid to this aspect – LED damage/life span reduction can occur in cold conditions – causing LED failures at a later stage.
7. LED bin selection- some LED bin selections are not as efficient as others, if the LEDs bin selection is later changed [to save production cost] the LEDs may be less efficient [the unit will be set to use more power + produce more internal LED/driver heat- again, this can affect/lower the products Ta ratings] if the LEDs are running close to their thermal limit-they may be more prone occasional unexpectedly high site temperatures – a good reputable manufacturer would not do this, but this is a practice we have noted in a few newly formed companies, who are often working on a tight start-up budget.
A supplier who checks the incoming stock’s performance/specifications against the original sample, can monitor for such variations, after checking the products lifespan is not affected -by any of the issues mentioned above.
Remember – IES files are made at perfect 25C ambient at 230V operation on a brand-new unit – in practice the product has to work onsite, over a period of time at varying input voltages/temperatures + with the heatsink performance impaired by dust build up between services – The IES file and product cost, does not indicate fitness for purpose in terms of reliability in particular sites.
A trial and error approach of testing various makes of hi bay products, may not prove to be so useful [or wise] for example:
If a make of luminaires fails after 30,000hrs, the purchaser may have already installed a large number of the inferior goods – say after 20,000hrs run time, they may feel so confident that they install many more units into sites – and by the time trial and error shows up a bad design, it could be at great expense and bother to the supplier and customers!
The reputation damage of the specifier on such a scale, would be hard to undo.
A much wiser method is to ask for proof of reliability testing in advance– in the form of a full holistic assessment with thermal tests, which show the units driver and LEDs/thermal paste still will work for 50,000hrs when running at the products maximum Ta rating – this may also give an indication, that additional Ta headroom has been given to account for tolerances in build and onsite temperatures.
We note every year, that new record breaking high temperature conditions occur -due to climate change, actuate thermal assessment of products will become a hot topic in the future.
As usual- there are reasons why one lighting product may be cheaper than another:
1.Sometimes manufacturer’s costs can be reduced by using a cheap [lower quality] thermal paste – which may have been stored for too long- or does not have the same lifespan as other more expensive thermal pastes.
2. Material costs can be saved by using a smaller heatsink /less thermal paste– so there is no additional headroom to act as a safety buffer –if onsite temperatures are slightly higher than expected. The Ta rating of the product would actually be the temperature the unit fails at [add tolerance variation/dust build up to this -and the product may have a lower Ta rating than expected]
3, Costs can be saved by not conducting CE certification or thermal testing – again newly formed start-up companies may not have the cash to conduct tests on all models- they may sell the goods in advance of certifying, in order to raise the cash to certify later – we have noted this many times, when looking at various manufacturers in the past, and we see no reason why this cannot occur on Hi bay products.
There is also a danger that less skilled designers may assume they can copy another product successfully – without having the same level of expertise. One danger of a kit built hi bay, is the product initially looks simple to copy- but remember we are dealing with electronics, combined with thermal path design/material properties and electrical safety – these are aspects which cannot be assessed by the naked eye – regardless of how impressive the product aesthetics/performance claims look!
When products are released without reliability and CE testing- there is no guarantee of reliability or safety, sometimes you may find a manufacturer has not included EN 62471:2008 [Photo biological safety] or ROHS certification, in such cases the customer would not know if the products would fail compliancy testing – leaving them legally venerable.
There are Lighting product suppliers in the industry, who do not check for certification, and will simply take the manufacturers word as proof – or will be shown falsified CE documents without having the knowledge to discern a genuine certificate from a fake one! There are also a small number of manufacturers, who will take deliberate advantage of this!
Many purchasers are unaware of these issues– only through examining products and requesting data have we become aware of the scale of the lack of full testing of goods – sometimes, if you spot a test standard missing, the manufacturer will have the test done on request, although should not be the purchasers job to ensure this- it is the responsibility of a purchaser to perform due diligence ,and check the product is fully certified [ this requires knowledge of the current required standards/directives- normally the domain of the design engineers]
There may be UK suppliers who will accept a high product failure rate –if they are still making a good profit [especially if the unit is the cheapest and sells very well]. However- this is of little consolation for the occasional unfortunate customer who’s experiences the inconvenience.
Companies do not always test for reliability - we have noted some LED manufactures have copied an existing product design [using the same driver and make/number of LED]. An assumption is then made, that the test results for the original unit also apply to their copied design.
Sometime only one model from a range has been tested – this can be acceptable if the unit represents the highest wattage in the range – or the design uses modules [even with modular design, care must be taken not to make assumptions]
A product may look very similar to a brand name design- but would use a slight different aesthetic – to avoid patent issues [this could possibly alter the thermal characteristics of the design- such as the temperature coefficient of the thermal path from LED to external air] the copied design may employ a cheaper make of thermal paste [as the customer would not know] and the electrical characteristics may vary slightly – this could be enough to render the design unfit for purpose in terms of reliability.
On a few occasions, when assessing manufacturers new products for consideration, we have requested thermal test from newly formed companies– only to receive an E mail stating that they have not tested yet! – and will forward the results soon, or they will conduct tests after a large order is placed! – So how did the company know what the product’s actual Ta limits were when they started to sell the products? The answer is – they make an assumption! This is gambling with the customer’s reputation and money at stake.
We will not name these companies – but they are out there, and still trading!
This brings back memories of false lifespan claims for LED GU10 lamps in the early days – where some manufacturers copied each other’s designs and product spec, claims in order to compete – after many premature failures, these life span claims were re-addressed and corrected.
The market exerts a pressure on manufacturers to compete on spec, /price – this can create a situation where the customer is misinformed -in order to get an initial foothold in the market, the company may employ better engineers/testing regime once they make enough profit – again this is of little consolation to their earlier disappointed customers and their UK suppliers.
Questions to ask the supplier /manufacturer regarding product reliability claims:
1. Has the design been thermally tested to show the product driver and LEDs, can cope with the stated Ta rating -as part of the products reliability testing?
2. Does the product have full CE certification – ask to view the EU declarations of conformity for the product – check the LVD/EMC and ROHS are up to date? [Including EN 62471:2008 [Photo biological safety] and EN 62493:2010 [exposure to magnetic fields, EMF- bio hazard] – ask to see the CE declarations. We also recommend the accreditation of test house used is verified [some test houses have their accreditation canceled if they break the law with false CE reports]
3. Ask what level of redundancy [spare LEDs] does the product have? - What will happen if two or three [or more] of the LED strings failed open circuit – will the product still continue to work reliably?
4. Ask if the product employs a soft start LED current function – to protect the LEDs in cold start conditions.
5. Ask if the product has a warranty that also covers lumen maintenance.
6. Ask if third party has checked the design for reliability- as CE testing is mainly concerned with safety- the initial reliability testing is done by the design team, a second opinion on the reliability data can confirm/dismiss the claims – providing a greater degree of assurance, and also reduce the possibility of design errors – and misunderstanding of Ta calculations for individual wattage versions and their uses [or non –use] of additional headroom.