This article examines various alternative street lamp replacement policies, and reports the result of an experiment with lamps. Lamps can be replaced individually when they fail, or a large number of lamps can be replaced after a given period, regardless of their failure rate. Which method is acceptable depends on whether the policy is viewed by the user, the supplier, the exchequer, or the auditor. Most codes of practice recommend a bulk change approach, because it has several advantages. The popular accepted standard is that group replacement, coinciding with the lamp cleaning cycle, is economically more efficient than burning to extinction. In assessing policy, it is crucial to know how long a low wattage lamp can remain in operation and continue to be economical in terms of operational costs and light output. The lifetime of a lamp cannot be predicted precisely and is a random variable. If a local authority decides to economise on lamps, extending the bulk change period and not changing the lamps may both be considered viable. The article then discusses the conditions for individual replacement to be economic, the evaluation of extension of lamp life, real economics, and service quality. The experiment measured the declines in the light output of 35W low pressure sodium lamps during their lives.
Samenvatting