Reflections on the luminous flux maintenance rate

The standard definition of the luminous flux maintenance rate is the ratio of the luminous flux of the lamp after being ignited at a given time point under specified conditions to its initial luminous flux, which is the definition of the "Standard for Architectural Lighting Terms" JGJ 119-2008.

Now the application of LED lights is more popular, according to the "LED indoor lighting application technical requirements" GB/T 31831-2015 provisions, the luminous flux maintenance rate of LED light sources and LED lamps should not be less than 96% after 3000h of operation; while should not be less than 92% after 6000h. This requirement is not high. For LED lamps that meet this requirement, their light decay shows a linear decline. When it reaches 24000h, the luminous flux maintenance rate is only 68%, which is lower than the life requirement of LED lamps. Therefore, qualified products should be better than this regulation.

Figure 1 Luminous Flux Maintenance Rate of LED Lamps

(The red dots are the standard required values, and the blue dots are the calculated values based on the standard requirements)

However, this regulation is a requirement for lighting products, therefore the products must meet it. Not only that, other standards such as the “Urban Road Lighting Design Standard” CJJ45-2015 also have similar regulations.

We also need to consider another issue, in addition to the product standard requirements, should the application scenario also have corresponding requirements? For example, the luminous flux maintenance rate of field lighting in high-level sports venues can be made special provisions to meet the needs of sports competitions and television broadcasts. At this point, FIFA has made regulations as early as 2007, recommending the use of constant lumen technology, and the luminous flux maintenance rate of the light source is close to 100% during its life cycle. This was epoch-making in the era of using metal halide lamps for sports lighting, and now entering the era of LED sports lighting, constant brightness technology still has practical significance, and it is easy to achieve constant lumen with a slight modification in the driver. Article 19.3.9 of the "Code for Electrical Design of Sports Buildings" JGJ 354-2014 stipulates that when using lamps with constant lumen technology, the maintenance factor of lighting design can be taken as 0.9.

Other application scenarios also need to be further explored, and considerations should be made from many aspects such as safety and economy.