Interest in the possibility of igniting flammable gases and dust by using light gained momentum some 25 years ago when the use of fibre-optic transmission and laser techniques began to be explored. Since that time, there has been a considerable amount of work exploring the various mechanisms for ignition that can occur. Inevitably the challenge has been to find the minimum light levels that can cause ignition and some generally accepted results have emerged. The remaining task is to convert these results into a code of practice, which will allow the techniques to be used safely.