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Many lighthouse services tod ay are removing or decommissioning traditional optics and installing new, smaller, self-contained devices. There are good economic reasons for doing this but sometimes there is a need to retain large traditional optics. In this case the choice of light source is important, fitting a modern 'off the shelf' lamp in a large optic can produce poor results. Over the last three decades light intensity measurements of several lighthouses have been carried out in order to determine their performance. During the course of this work several experimental light sources have been measured and their results compared with existing light sources. This process started in 1971 with the first measurement of a lighthouse fitted with a paraffin vapor burner. Several experimental light sources were temporarily installed and compared with existing light source. Since then experiments have continued and resulted in the replacement of 3.5 kW lighthouse lamps in rotating optics with readily available 1 kW metal halide lamps. Within recent years, in a drive to reduce energy requirements for potential use of solar power, some small low power lamps have been temporarily installed in large optics to see how they performed. In many cases the small size of the light source has caused problems of poor performance including short flash duration and low intensity. Various techniques such as envelope etching, reeded diffusion and lamps clusters have been used to enhance the performance of these low power light sources in order to optimize their use within traditional optics. The results of various light measurements are shown in this paper, together with details of problems encountered during the experiments.
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