The main conclusions and findings of this investigation may be summarized as follows:- (1) It is possible to make illumination surveys underground with a considerable degree of accuracy, and an instrument for this purpose, which can also be used as a photometer, is described. (2) A method of plotting such surveys as illumination contours is explained, and a number of examples of surveys showing the areas of face illuminated to different standards for different systems of lighting is given. (3) These surveys show the great improvement which has taken place in face lighting within recent years; also that several types of portable lamp are now available to the industry which illuminate the work being done by the underground worker to, and in some cases well beyond, the minimum of the 0.1 ft. -c. standard recommended in the Third Report of the Nystagmus Committee. (4) Where conveyors are used at the face, lighting from the mains, as at present adopted and arranged, while providing better general illumination, is inferior for individual work to that obtained by several forms of modern portable lamp. (5) For a portable electric hand -lamp, the best reflectors are those which may be fitted inside the well -glass. The best reflecting surface is the matt white surface of photometric paint. (6) The standard of illumination may be greatly improved by the / the use of high- efficiency bulbs, especially in combination with the photometric paint reflector. Care, however, should be taken to ascertain that such bulbs have passed the life test (600 hours burning). (7) While the cap -lamp is rapidly growing in popularity, the distribution of the light which it gives leaves room for much improvement, especially for work at the coalface. Two new reflectors, designed to give a more uniform light distribution, are described. (8) In underground illumination glare is to a certain extent inevitable, but suggestions are made for reducing its effect. For hand-lamps the best solution to the problem is the combination of opal well -glass and photometric paint reflector, with a high efficiency bulb to compensate for light losses due to absorption. Tinted bulbs and glasses seem to effect very little improvement. (9) For reducing the effect of glare from cap -lamps, two methods are suggested (a) the use of one of the new reflectors already described (b) the use of a "flashed" opal glass in one of the modern lamps of 3 or 4 watts rating. (l0) Under all circumstances, "mixed lighting" should be avoided.