Illuminating the industry with Andrea

What’s in the Box Matters.

Have you ever bought a product, only to discover that what is promised on the packaging is not what you get inside? This is a common issue in the lighting industry, especially when it comes to the quoting of ‘nominal lumens’. In the real world, nominal lumens offer zero real-world value for the end user. But why is this so, and what is the difference between Nominal, Effective and Residual lumens?

  • Nominal lumens is a theoretical lumen value that has been calculated by the LED manufacturer without considering where or how their LED board will be used. I do not mean the LED fitting – I am talking about the LED chips themselves that still need to be housed in a light.
  • Effective lumens is the output value of a complete light fitting that is measured at Ta (ambient temperature) of 25°C after all the electrical and optical losses are considered, and upon reaching thermal stability.
  • Residual lumens is a function of the L&B specification over time and temperature. In other words, the remaining lumens that are available from a fitting after a predetermined time (primarily its warranty period) and temperature. It is the measure of light that your fitting will give as it ages, and it is sometimes referred to as design lumens. This is an important measurement as ambient temperature above 25°C will greatly affect the claimed performance.

Allow me to use an analogy. If I sold a stand-alone car engine with a theoretical fuel consumption of 4 litres per 100km, this information would only really be valuable to a car manufacturer (this would be the nominal lumen value in a light). A car buyer, however, would have no interest in what the engine can theoretically do – buyers want to know what the car manufacturer accomplished with the engine. The effective lumen equivalent would be the engine’s performance on day 1, while residual lumens would be the engine’s performance five years down the line.

So why do some illumination companies still use nominal lumens as a measurement and on their packaging? Simple – the numbers look great, and they are banking on the end user not knowing any better. Or less sinister but no less reckless, they cannot measure the performance of their own lights and fittings… and this is far more prevalent than what you would think.

Nominal lumens are useless to anyone other than manufacturers and I would question anywhere that you see this type of information stated on a finished product. Effective lumens are the only meaningful declaration to look for on a box – keep in mind that this too is up for debate as it does not and cannot take the final application and use into account. A lighting design that indicates residual lumens offers the best available view of what your luminaire or installation is going to produce over its commercial life, and reigns supreme as a professional indicator. What is on the box should matter all the time – any industry should be able to stand alongside the claims it makes on the packaging to consumers with the functionality those consumers can expect from the fitting inside.


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