Light pollution is a side effect of industrial civilization. It comes from sources such as domestic lighting, advertising, commercial properties, offices, factories, streetlights, and lit sporting venues. It is most severe in the highly industrialised, densely populated areas of the United States, Europe, and Japan, but even relatively small amounts of light can be noticed and create problem. \"Light pollution\" is a term that is used to refer to light that people find annoying. Some skeptics claim that light pollution should not be compared with \"real\" pollution, arguing that any instance of stray light has no long term effect. This is because unlike traditional forms of pollution, light pollution is not persistent. The amount of light pollution at any given time is directly related to the amount of artificial light that is being emitted at that time, meaning that if all artificial lights were immediately switched off, the visual effects would cease immediately. Critics who take this point of view contend that in some cases, light pollution should not even be worried about. Campaigners wishing to reduce light pollution, however, argue that it is unrealistic to expect populations to ever switch off light en-masse, due to industrial society\'s economic reliance on artificial light. They argue, therefore, that it is a problem synonymous with traditional forms of pollution, where trends in society that are difficult to stop have long term negative effects. Campaigners contend that light pollution must be dealt with by changing the habits of society so that light is used more efficiently, with less light being wasted and directed towards places that are undesirable. Several industry groups also recognise light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides information for its members about light pollution, the problems it causes, and how to reduce the pollution . Because not everybody is irritated by the same sources of light, the term is subjective. It is common for one person\'s light \"pollution\" to be light that is desirable for another. This is often the case with advertising material, such as when an advertiser wishes for particular lights to be brightly visible, even though others find them annoying. Other types of light pollution are more certain. For instance, light that accidentally crosses a property boundary and annoys a neighbour is generally wasted and pollutive light, as it is of no use to anyone. Disputes are still common, however, when deciding if it is necessary to do anything about it. Differences in opinion over what light is considered reasonable, and who should be responsible, means that negotiation must sometimes take place between parties. Authorities have also taken a variety of measures for dealing with light pollution, depending on the interests, beliefs and understandings of the society involved. Measures range from doing nothing at all, to implementing strict laws and regulations about how lights may be installed and used. Disruption of the ecosystem Life evolved with natural patterns of light and dark, so disruption of those patterns influences many aspects of animal behavior (Longcore and Rich 2004). Light pollution can confuse animal navigation, alter competitive interactions, change predator-prey relations, and influence animal physiology. Reducing light pollution Reducing light pollution implies many things, such as reducing sky glow, reducing glare, reducing light trespass, and reducing clutter. The method for best reducing light pollution, therefore, depends on exactly what the problem is in any given instance. Possible solutions include: Improving lighting fixtures, so that they direct their light more accurately towards where it is needed, and with less side effects. Adjusting the type of lights used, so that the light waves emitted are those that are less likely to cause severe light pollution problems. Evaluating existing lighting plans, and re-designing some or all of the plans depending on whether existing light is actually needed.