What is maintenance factor in LED Street Lighting

Analysis on maintenance coefficient of LED road lighting

Abstract: in the lighting design, an important work is to determine the lighting maintenance coefficient, which should consider the installation, use and maintenance costs and other factors. In recent years, with the maturity of LED technology, LED lighting products have been widely used in the field of road lighting. However, due to the difference between LED and traditional light source, there are some differences in the determination of maintenance coefficient in the application of LED lighting products. This paper will discuss how to determine the maintenance coefficient in the application of LED lighting.

Preface

The illuminance standard values specified in CJJ45-2006 are the average brightness values on the working surface or reference plane. It is the average luminance (illuminance) value used in the design and calculation after taking into account the attenuation of light source planned replacement time flux and the decrease of lamp efficiency due to pollution (i.e. maintenance coefficient). Therefore, in the lighting design, an important work is to determine the lighting maintenance coefficient, which should comprehensively consider the installation, use and maintenance costs and other factors.
In recent years, with the maturity of LED technology, LED lighting products have been widely used in the field of road lighting.

However, due to the difference between LED and traditional light source, there are some differences in the determination of maintenance coefficient in the application of LED lighting products. This paper will discuss how to determine the maintenance coefficient in the application of LED lighting.

Definition and calculation method of maintenance coefficient

According to the terminology standard for building lighting (JGJ / T 119-2008), IESNA lighting manual (9th Edition) and maintenance of outdoor lighting system cie154:2003, the maintenance coefficient refers to the average illumination or average brightness of the lighting device on the specified surface after a certain period of service and the average illumination or brightness obtained on the specified surface when the device is newly installed under the same conditions Than. The factors affecting the value of maintenance coefficient include luminous flux maintenance rate of light source, residual rate of light source and pollution of lamps and lanterns, the calculation method is as follows:

MF= LLMF x LSF x LMF

Where:
MF — maintenance coefficient
LLMF — luminous flux maintenance system rate at the end of the service life of the light source, which shall be determined according to the product data of the manufacturer
LMF — maintenance coefficient of lamp pollution, its value is related to lamp wiping cycle, which can be determined according to table 1,

LSF — the failure rate at the end of the service life of the light source, which is related to the power of the light source, switching frequency and power supply accessories, but the influence of the damage of the light source on the maintenance coefficient can be eliminated by replacing the damaged light source in time.

Table 1 pollution maintenance coefficient of lamps and lanterns

Lamp protection level	Pollution classification	Maintenance period (years)
		1	1.5	2	2.5	3
IP5X	High pollution	0.89	0.87	0.84	0.8	0.76
	Medium pollution	0.9	0.88	0.86	0.84	0.82
	Low pollution	0.92	0.91	0.9	0.89	0.88
IP6X	High pollution	0.91	0.9	0.88	0.85	0.83
	Medium pollution	0.92	0.91	0.89	0.88	0.87
	Low pollution	0.93	0.92	0.91	0.9	0.9

It can be seen from formula (1) that when LED lighting products are used in road lighting, the main factor affecting the maintenance coefficient of LED lighting products is the luminous flux maintenance rate of light sources. Therefore, the research focus of the research on the maintenance coefficient of LED products in road lighting applications is mainly the difference of luminous flux maintenance characteristics between LED light source and traditional light source.

Comparison of luminous flux dimension
characteristics of light sources

The maintenance coefficient due to the attenuation of luminous flux of the light source is determined at the end of the actual service life of the light source. Therefore, in order to study the difference between LED and traditional light source, it is necessary to study the definition of LED light source life and the difference between LED light source and traditional light source such as high pressure sodium lamp.

★ a. definition of light source life

The life of the light source is an important index to evaluate the performance of the light source. The life of the light source can be divided into full life, average rated life and effective life. The effective life depends on the luminous performance of the light source.
When the light emitted by the light source drops to 80% (or 70%) of its initial value, its lighting time is defined as its effective life or economic life. The time from ignition to failure of the light source is called the full life of the light source, and the lighting time when half of the light sources fail to work is called the average rated life of the light source.

For example, according to the national standard “high pressure sodium lamp” GB / T 13259-2005 and metal halide lamp (sodium thallium indium Series) performance requirements (GBT 24333-2009), the service life of high pressure sodium lamp and metal halide lamp is the cumulative time when the luminous flux maintenance rate of the light source meets the requirements of this standard and can continue to burn to 50% of the light source failure.

Because the LED light source in the normal use of less sudden failure, but with the growth of the use of time, luminous flux continues to decline, so the current international use of effective life (70%) to evaluate. For example, “performance requirements for LED lamps for road lighting” (GB / T 24907-2010), the cumulative ignition point of LED road / tunnel lighting products shall be maintained under the test conditions of GB / T 24824-2009 Standard Test methods for LED modules for general lighting. During the ignition process, the luminous flux maintenance rate meets the requirements of this technical specification and the luminous flux maintenance rate decreases to 70%.

★b. Attenuation law of luminous flux of light source

Traditional light source
In the process of ignition, the luminous output of traditional high-strength gas discharge lamp will gradually decrease. The luminous flux attenuation of light source is affected by many factors, including light source power, electrode decay, arc tube blackening caused by sputtering, chemical balance change in arc tube and ballast performance change. Frequent switching on and off of lamp will also accelerate luminous flux attenuation of light source.

LED light source
In 2011, the United States issued ies tm21 (projecting long term lumen maintenance of LED light sources) standard, which is applied to LED packaging, LED array and LED module with external drive control. The standard specifies a method to calculate the luminous flux maintenance rate of LED light source by using ies LM80 test data and exponential attenuation as luminous flux attenuation model. At present, this method has been widely used as a method to judge the luminous flux attenuation of LED.

Therefore, when the maintenance coefficient is calculated according to the effective life (70%) of LED products, the luminous flux maintenance rate of the light source is 0.7; if the maintenance rate of the light source is expected to be increased, the service life of the lamp shall be shortened; when the effective life of the LED product is shortened to 0.7 times (70%), the luminous flux maintenance rate of the light source shall be taken as 0.78.

Comparison of maintenance coefficient between LED
and traditional light source

According to the values determined above, the maintenance coefficient of LED light source and traditional light source in lighting design can be calculated, as shown in the table 2:

Table 2: Comparison table of maintenance coefficient between LED light source and traditional light source in lighting design

Maintenance week stage (year)	High pressure sodium lamp			Metal halide lamp (quartz)			Effective life of LED			Led service life
	High pollution	Medium pollution	Low pollution	High pollution	Medium pollution	Low pollution	High pollution	Medium pollution	Low pollution	High pollution	Medium pollution	Low pollution
1	0.8	0.81	0.82	0.71	0.72	0.72	0.61	0.62	0.62	0.68	0.69	0.7
1.5	0.79	0.8	0.81	0.7	0.71	0.72	0.6	0.61	0.62	0.67	0.68	0.69
2	0.78	0.79	0.8	0.68	0.69	0.71	0.59	0.6	0.61	0.66	0.67	0.68
Note: 1 the protection level of lamps is ip6x, 2. Choose the road grade as the secondary trunk road, and the lighting rate is 96%.

It can be seen from table 2 that in the case of traditional lighting control mode, the luminous flux maintenance rate of LED light source is lower than that of traditional light source, so the lighting maintenance coefficient adopted in lighting design is relatively low, and the value is only about 0.6. At present, the British road lighting standard bs5489-1-2013 has a maintenance factor of 0.58 for LED road lighting products. When choosing LED light source, in order to ensure that its energy consumption is not higher than that of traditional light source, the luminous efficiency of LED light source should not be less than 130% of that of high pressure sodium lamp system and 116% of that of metal halide lamp system.

As a new light source, LED has its own characteristics, especially due to its immature products, there are also a series of problems in lighting applications. In order to better guide the scientific development of LED road lighting, give full play to its own advantages, on the basis of creating a safe and comfortable travel environment for the people, effectively reduce the lighting energy consumption and reduce the maintenance cost of urban lighting, it is suggested to carry out the following work:
1) Further research on the economic and technical analysis method of LED road lighting;

2) study the lamp pollution reduction evaluation method
3) The evaluation method of LED light source attenuation based on different temperature is studied
4) To make full use of LED’s characteristics of easy dimming, intelligent control, constant illumination control and other methods are adopted to reduce the operation energy consumption caused by low maintenance coefficient
5) Further develop LED technology to improve the efficiency and stability of LED products.