ANCIENT LIGHTS, a phrase in English law for a negative easement (q.v.) consisting in the right to prevent the owner or occupier of an adjoining tenement from building or placing on his own land anything which has the effect of illegally obstructing or obscuring the light of the dominant tenement. At common law a person who opens a window in his house has a natural right to receive the flow of light that passes through it. But his neighbour is not debarred thereby from building on his own land even though the effect of his action is to obstruct the flow of light thus obtained. Where, however, a window has been opened for so long a time as to constitute immemorial usage in law, the light becomes an "ancient light," which the law protects from disturbance. The Prescription Act, 1832, created a statutory prescription for light. It provided (s. 3) that "when the access and use of light to and for" (any building) "shall have been actually enjoyed therewith for the full period of 20 years with out interruption, the right thereto shall be deemed absolute and indefeasible, any local usage or custom to the contrary notwith standing, unless it shall appear that the same was enjoyed by some consent or agreement, expressly made or given for that purpose by deed or writing." Since under the statute an "inter ruption" in order to prevent the right accruing must be one of at least a year, the period of prescription is really only 19 years. But the right given by the statute is inchoate, unless and until the dominant owner's claim is decided by the court, and the period of prescription must be the years immediately preceding the action raising the question. But in the meantime, however long the enjoyment may have been, the dominant owner's right is just the same, and the origin of his right is just the same as if the act had never been passed. These principles were laid down in 1904 by the House of Lords in the leading case of Coils v. Home and Colonial Stores, Ltd. (1904, A. C. 179) . There has been much difference of judicial opinion as to what constitutes an actionable interference with "ancient lights." On the one hand, the test has been prescribed that if an angle of 45°—uninterrupted sky light—was left, the easement was not interfered with, and, while this is not a rule of law, it is a good rough working criterion. However, it has now been decided by the House of Lords in Coils v. Home and Colonial Stores (supra) that there must be a privation of light substantial enough to render the occupation of the house or building uncomfortable according to the ordinary notions of mankind and (in the case of business premises) to prevent the plaintiff from carrying on his business as beneficially as before. See also Kine v. Jolly (1905, 1 Ch. 48o). The ordinary remedy for a disturbance of "ancient lights" is an injunction. Under the act commonly called Lord Cairns' Act, 1858, however, the court has power to grant damages in lieu of an injunction even before any damage has been done to the premises of the plaintiff (Leeds Industrial Co-operative Society, Ltd. v. Slack, 1924, A.C. 851). This jurisdiction is exercised only when the possible damage is certain to be small. (See EASEMENT.) There is, in Scots law, no special doctrine as to "ancient lights." The servitude of light in Scotland is simply the Roman servitude non officiendi luminibus vel prospectui. (See EASEMENT and ROMAN LAW.) The same observation applies to the Code Civil and other European codes based on it. The doctrine as to ancient lights does not prevail generally in the United States. In a considerable number of the more important British dominions the acquisition of a prescriptive right to light and air has been abolished.