It is difficult to accurately compare burn times/lighting times between different manufacturers of hands-free lighting products, as the figures for reference from each manufacturer that shows their product offering has an advantage over competing products. . Some manufacturers report burn time statistics calculated several times after the emitted light power is useful (down to the last photon). Petzl makes it clear that it has a policy where it stops considering lighting to be effective when the lighting level (for standard hands-free lighting) drops below 0.25 lux at a distance of 2 meters. This figure is chosen as a rough equivalence 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 must provide to be fit for purpose. Petzl applies an extensive testing procedure to produce the claimed statistics. The tests are carried out in the laboratory on five identical headlamps randomly selected from the production line. These headlamps are individually tested with two new sets of batteries, identical to those supplied with the product. Since temperature fluctuations can affect results (especially 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 claimed lighting performance statistics. This rigorous and clearly defined testing process provides precise performance indicators, which can be effectively evaluated on different products in the range by the consumer in order to match their requirements in relation to performance...... middle of paper.. .... primary battery (especially alkaline), because they generally experience less self-discharge when not in use than secondary batteries. If the device is operating on secondary batteries, there are many more potential causes for difference in duration than standard primary batteries. In addition to the problems mentioned above that affect all batteries, there are other problems specific to secondary batteries. Problems that affect secondary batteries are: • Cell age • Battery life • Initial charge level • Cell condition/previous treatment • Memory effect (especially NiCd) • Loss of electrolyte • Venting (a release of active battery chemicals)These can be considered as the main reasons for a decrease in battery life, hence burning time/lighting time. Some of these issues affect primary batteries, for example ventilation, but they are usually only rechargeable..