It is difficult to accurately compare burn times/lighting durations between hands-free lighting products from different manufacturers as each manufacturer's benchmark figures show that its product offering has an advantage over competitors' products. Some manufacturers report burn time statistics calculated for very long times after the emitted light output is useful (down to the last photon). Petzl clearly states that it has a policy whereby it ceases to consider a lamp effective when the illumination level (for standard hands-free lighting) drops below 0.25 lux at a distance of 2 meters. This figure is selected as an approximate equivalent to the lux value generated on a dark night by a full moon. They consider this light output to be the minimum level that a hands-free lighting device should provide to be fit for purpose. Petzl carries out an extensive testing procedure to produce the advertised statistics. Tests are conducted in the laboratory on five identical head torches randomly selected directly from the production line. These head torches are individually tested with two new sets of batteries, identical to those supplied with the product. Since temperature fluctuations can influence results (particularly the discharge rate of battery technologies), the test environment is controlled at 20° Celsius to ensure statistically significant results. These ten sets of statistically reliable results are averaged for each parameter to provide the definitive final performance statistics of the advertised light. This rigorous and clearly defined testing process provides precise performance indicators, which can be effectively evaluated by the consumer across the various products in the range to meet their needs with respect to performance... middle of the paper... primary battery (especially alkaline) as they generally experience less self-discharge when not in use than secondary batteries. If the device operates using secondary batteries, there are many more potential causes of life differentiation compared to standard primary batteries. In addition to the problems mentioned above that affect all batteries, there are other problems specific to secondary batteries. Issues affecting secondary batteries are: • Cell age • Battery cycle life • Initial charge level • Cell condition/past treatments • Memory effect (especially NiCd) • Electrolyte leakage • Venting (a release of chemicals battery life) These can be seen as the main reasons behind the decrease in battery life and therefore in the autonomy/duration of the light. Some of these problems affect primary batteries, such as venting, but generally they are rechargeable only.