Don’t be misLED by false product performance figures

August 18, 2017

                                

This month blog looks at how sales information provided by some manufacturers and suppliers, differs from the actual lighting product’s performance, when stating the products true efficacy.

 

Please note: efficacy is the term used to describe a products total efficiency, and not the LEDs specification, but the efficiency of the complete product –which includes driver loss/optic loss and efficiency at the actual working temperature [also taking power factor and power consumption at differing input voltages into account].      

  

We have seen many manufacturers quote the specifications for the LED used in the product-as being the product actual specification, for example:

 

You may hear of a COB floodlight advertised as having an efficacy of 155 lumen per watt- along with its Ta rating and other product specifications!

 

Why is this misleading? – Because the product manufacturer is not only quoting the LED component specification [and not the luminaires] but they are also quoting the LED manufacturers 25C test results- for the LED chip without driver/optic losses!

 

For example:

 

We noted an advert for a floodlight using a well-known COB – claiming 155 lumens per watt on the product’s advertisement [though we know it to be 94 lumens per watt in practice] the advert refers to the fact that a company introduced a 155LPW COB in 2016.

 

Looking at the data sheets for the 158 LPW COB used in the product, we can see the data sheet states an efficiency of 158LPW – but only at an LED case temperature of 25C!

 

But when running in a typical flood light design at 25C ambient– the COB can run from 60C to 85C [depending on heatsink/drive current].

 

The 25C LED case temperature could be achievable if:

 

A. the LED light is on a short switch on-time PIR sensor- at a Ta on /or below 25C [but if used often can heat up].

 

B. The luminaire is working in a freezer – but the LED/luminaire will create heat – thus adding to the freezers power consumption – this may not be economical. 

 

A 60W COB flood running in an ambient of 25C, in practice would run at around 60C to 85C,

 

The data sheet for the COB, states the following light outputs when running at 26.5W:

 

At 25C [case]               At 85C [case]

 

4187Lm                         3755Lm

 

This calculates as 158LPW at 25C [case] and 141LPW at 85C [case]

 

Bear in mind this does not include optic losses – [but as the floods don’t use diffusers] a 5% optic loss would make the light output as 3567Lm, or 134.6LPW

 

Note: The COB company are not providing any misleading information here– the data is for engineers to use, and should not be used as sales data – unless the COB in the product is actually running at 25C [case temperature] in its intended application!  

 

Important note: we still have not included driver loss [usually 14% to 20% depending on load matching and make of driver]!

 

So, with an 80% efficient driver [and no optics] the total efficacy would now be 113.1LPW.

With a 90% efficient driver [and no optics] the total efficacy is 127.7LPW

 

Important note: So far in our calculations -the LED is only running at 26Watts –the same LED is intended for high power use [84W], but the LED efficacy drops as follows:

 

At 85C [case] running at 84W, the same LED outputs 9881Lm = 117.75LPW

 

With an 80% efficiency driver, the total power consumption is 105W or 94.2LPW

 

With a 90% efficiency driver, the total power consumption is 93.3W or 106LPW.

 

However- a 90% efficiency driver is more expensive than an 80% one. 90% load/source matching may not be possible, if the forward voltage/current of the LED, does not match the specification/power band area of the driver [drivers need to be load matched or driver efficiency will drop]

 

It is worth noting, that the product manufacture could claim to use a 90% efficient driver- but could only be using it at 80%. 

 

More variables! -Another pitfall when looking at efficacy of lighting products –is the fact that not all drivers consume the same amount of power at different input voltages –so a product may be efficiency tested at 220V – but at 230V to 240V the power consumption may rise dramatically [lowering the efficacy when working in real world conditions]

 

Advertisements also usually quote the efficacy for the 6000K LED ranges - not 3000K or 4000K which may have less efficiency- so a 3000K/4000K product’s actual efficacy may not meet the expectations raised by the advertised 6000K unit. 

 

Manufacturers also, often round up the products power consumption figures [E.G. a 195W or 205W unit will be classed as a 200W]. A LM79 test can clarify this- it is good practice to know all the variables, as they can all add up in the same direction, and lead to miscalculations regarding light output and power consumption. 

   

So, when a product manufacturer tells you they have 155 lumens per watt LEDs on the product – we would recommend that you check the IES files and actual power consumption, but be warned – it is very easy to edit an IES file intended for another product, sometimes you can open the file in Microsoft Notepad – within the text, you may see the name of the original owner of the IES file [indicating that the data was for another product and was manually entered and may not be correct]  

When available, a LM79 report from a CNAS accredited test house, can give you very accurate/real world figures that can be relied upon- [ showing actual light output and power consumption] but it should be considered if the products power consumption varies with input voltage.

 

We note a well-known COB manufacturer has announced a 174LPW COB [at 25C /low power use] – but at 85C /65W the chip runs at 123LPW [not including driver and optic losses] – we expect this 174LPW figure may be soon used by some manufactures – creating a greater difference between advertisement quotes and the product specification in actual reality.

 

At MGLites, unless otherwise stated – we refer the products genuine efficacy and the products delivered lumens [which includes actual LED temperature in use + driver losses + optic losses] we also check that the power consumption/power factor remains the same or better, when the supply voltage varies onsite.

 

We hope this blog helps to clarify some of the pitfalls, when selecting a LED product from a non-technical wholesaler- we believe there are many UK purchasers, who do not fully understand how to interpret such data- or even know when it is wrong or misleading.

 

Many manufacturers think it is unfair to compare product prices of units with false specifications against ones which are genuine -especially if such false a product specification does not actually exist.

 

Often these goods are perceived as being cheaper [when comparing by specification] with the purchaser unaware, that they are being misLED!