LED performance, the gap between advertised and real luminous flux (2)

In this previous post we have written about how the brightness (luminous flux) of a LED lamp varies with the operating temperature and have said that some producers only advertise the performance at an optimal, lab temperature, of 25 ºC.

We have also shown that the savings promised by LED technology are real only for high performance LEDs.

Now we will talk about another, more serious, aspect about the advertised performance of LED lamps: false advertised brightness.

The brightness (luminous flux) of a light source is impossible to measure at home. One needs specialized measurement equipment and knowledge to measure the luminous flux and some producers take advantage of this aspect to claim their LED lamp has a lot more lumens than in reality.

Lets look at the specs of the LED bulb below:

The producer of this particular light bulb claims his "High Brightness 5W LED Bulb" has a impressive 550 lumens. But is it true? How can we find out the answer without a lab to do the measurements?

Fairly easy, we use comparison and common sense.

For comparison we go to the website of a known brand, in the case of LED bulbs this can be: Samsung, Philips, Osram, Toshiba and we look at the specifications of a LED bulb with similar wattage:

 The Samsung LED bulb above has 490 lumens for 6.5 Watts and we can find products with similar specifications at the other brands too. Thus, our common sense tells us that the little known producer that claims his bulb has 5 Watts and 550 lumens is not telling the truth.

 The savings promised by LEDs occur only if the producer gives honest information about his product`s performance.
 

LED performance, the gap between advertised and real luminous flux (1)

LED technology has made the decision to buy lighting products very complicated. We are promised important savings in energy and maintenance costs and asked in return to pay a higher price, at times dozens of times higher than other lighting technologies: incandescent, halogen or fluorescent.

But are the savings always real?  
The answer is: it depends...

In this series of articles we will discuss the elements that can define the answer to this question.

Brightness

When we want to replace our old lights with LED or have a new project that needs light, the first thing we take into consideration is brightness. In tech talk this is measured in lumens and is called luminous flux. Unlike a few years ago, today we can see the luminous flux on most lamp packing at the supermarket or find it on the internet at almost all online shops that sell lamps.

 It got like this because brightness has became a very important criteria in the buying decision, so important that some producers/distributors or retailers are willing to give misleading information just to score points in the race for the customers wallet.

Therefore, in the case of some products there is a gap between the advertised brightness and the real, so large that can turn the hole savings argument to buy LEDs on its head.

How temperature affects LED brightness

The performance of LEDs is greatly influenced by ambient and junction temperature (the one inside the LED) as every degree beyond 25 ºC decreases its brightness (lumen output). The amount of lumens lost is what makes buying LED lamps complicated.

A good LED, a Nichia SMD LED for example, will loose less than 10% if the nearby ambient temperature reaches 60 ºC, a very common value inside most fixtures.

 

On the other hand, a not so good LED, an OEM 3258 SMD for example,  will loose at 60 ºC almost half of its brightness.

Most LED producers advertise their products with the performance at 25 ºC but only some mention the temperature at which it was measured and even fewer provide a graph to show the connection between the two values, as the ones above.

Therefore, are the savings promised by LEDs always real?
The savings are real for a high performance LED and false for a low performance one.

When buying LED technology we should always take in consideration this aspect, especially if the price of the product is low or the producer is not a known brand.

Some top brands of LEDs: Cree, Nichia, Osram, Philips, Bridgelux, Citizen...