Life cycle cost comparison of high-pressure sodium and light-emitting diode luminaires in street lighting

Purpose: Cities and municipalities are facing a great challenge in 2015 when the widely used high-pressure mercury lamps are banned from the European Union market. This results to approximately 18 million lamps to be changed to other light source technologies suitable for outdoor lighting. The most probable replacement technologies are high-pressure sodium and light-emitting diode luminaires. The article provides economic information for the cities and municipalities to use when making the decision on the choice of technology. Methods: A life cycle cost analysis was conducted for the high-pressure sodium and light-emitting diode luminaires including the investment costs, operating costs and residual value over 30-year time frame. The investment costs included the purchase prices of all parts, freight and installation costs. The operating costs accounted for the energy and maintenance costs, and the residual value was calculated using the 25 % estimate of the initial purchase price. The approach of the calculation considered only the luminaires to be installed; the scope of the study excluded the previous installations, which may contain any light source technology or be inexistent. The analysis excluded the poles, wiring and other infrastructure. A sensitivity analysis additionally studied six scenarios, in which relevant calculation parameters were changed. Results and discussion: The life cycle cost analysis of the two road lighting luminaire technologies showed that the HPS luminaire was normally a more economical solution compared to the light-emitting diode (LED) luminaire. The total life cycle costs of the HPS luminaire were 45 % lower than those of the LED luminaire per kilometre. However, the scenarios in the sensitivity analysis indicated that there were circumstances where the cost-efficiency of the LED luminaire was particularly improved. In order for the LED technology to become fully competitive against the HPS technology, several scenarios have to take place simultaneously. The life cycle costs of the LED luminaire were reduced compared to the HPS luminaire by increased electricity price, exclusion of spot replacements, reduced purchase price and modularity of the LED luminaire. Conclusions: Despite the greater luminous efficacy, the LED luminaire was found to have greater life cycle costs compared to the HPS luminaire. However, the LED technology is expected to become more economical in the future due to the development in luminous efficacy, improved product quality, reduction in the purchase price and the enhanced competition in the LED segment. Despite the unfavourable cost structure, the LED technology offers other benefits, such as lighting controls and colour characteristics.