LED bulbs technical specification and testing procedure for solar home systems

Abstract

The definition of technical specifications and the corresponding laboratory procedures are necessary steps in order to assure the quality of the devices prior to be installed in Solar Home Systems (SHS). To clarify and unify criteria a European project supported the development of the Universal Technical Standard for Solar Home Systems (UTSfSHS). Its principles were to generate simple and affordable technical requirements to be optimized in order to facilitate the implementation of tests with basic and simple laboratory tools even on the same SHS electrification program countries. These requirements cover the main aspects of this type of installations and its lighting chapter was developed based on the most used technology at that time: fluorescent tubes and CFLs. However, with the consolidation of the new LED solid state lighting devices, particular attention is being given to this matter and new procedures are required. In this work we develop a complete set of technical specifications and test procedures that have been designed within the frame of the UTSfSHS, based on an intense review of the scientific and technical publications related to LED lighting and their practical application. They apply to lamp reliability, performance and safety under normal, extreme and abnormal operating conditions as a simple but complete quality meter tool for any LED bulb.

These tests have been applied to a group of 14 low-cost direct current LED bulbs and the accomplishment of the proposed requirements is analyzed.

Introduction

LED lamps have introduced a new way of electric light generation from an electronic source which is overpassing conventional technologies traditional barriers of light efficiency and reliability [1] and have become the optimum solution for solar home systems considering “cost effectiveness and robustness” [2]. For example, the luminous flux of 8-W Compact Fluorescent Lamps (CFLs) is around 400 lm while low/medium class LED bulbs can overpass this value with only 5 W, and is expected to reach soon peak efficacies over 200 lm/W and to reduce their basic cost up to 95% by the year 2030 [3], [4].

Moreover, this type of devices are built without any amount of hazardous elements like mercury or lead which is one of “the most imperative features of solar-powered LED lighting” installations [5]. Comparing CFL and LED bulbs on equivalent quality basis with respect to the expected lifetimes, the first ones have, on average, 12 times higher potential environmental impact due to reduced hazardous and rare metals [6] and there are many investigation projects to minimize the usage of hazardous metals in the LED manufacturing process [7]. These bulbs, when broken, must be treated as any other electronic device with no battery such as any small home appliance: preferably repairing them and, when it is not possible, disassembling them and reusing or recycling their different pieces. Many national and local policy and legislation are being created along this basic principle [8].

Concerning the specific area of the Solar Home Systems (SHSs), the off-grid electric lighting solutions have evolved in the last decades from the initial combination of fluorescent lamps and small incandescent ones [9], [10] to CFLs [11], [12] and finally to LED bulbs that are expected to grow at a very significant rate, especially in developing countries [13]. For example there is an estimation of 40–45% year-on-year growth in Africa through 2015 [14]. There are some particular characteristics that make it very easy to relate the SHSs and the LED lamps. The electronic nature of the semiconductor crystal, which acts as the new light source, works on low DC voltage and can be easily adapted to solar energy generators and batteries. Thus, this make this technology a very promising opportunity in SHS, substituting the current CFLs.

In the past, the quality of SHSs in general, and CFLs in particular, was impelled with the elaboration of many dedicated norms designed by different entities that, in many cases showed important differences in their requirements and specifications [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. In this situation, the collaboration between worldwide experts financed by the EU crystalized in the Universal Technical Standard for Solar Home Systems (UTSfSHS) in order to unify technical and procedure criteria [25]. This norm inspired other specifications like the one of the Bolivian IDTR program [26], [27] or the Peruvian PER project [28].

Now it is necessary to adapt the UTSfSHS to the new LED lamps and, consequently, this paper proposes a specific technical specification for this kind of lamps when used in decentralized DC Photovoltaic Rural Electrification (PVRE) applications together with its required quality tests.

The proposed technical specifications and testing procedures have been applied to a representative collection of different models of 12V_DC LED bulbs acquired in the current SHS market. Results are discussed and they illustrate the relevance of the technical specification proposed in this work and the current state of the art of LED bulb lamps.