This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Printing With Electric Light. For studio work and where a large amount of printing is done, a 32 candle-power incandescent electric bulb, which can be arranged along the lines of illustration No. 9, is recommended. This illustration represents one end of a dark room, fitted with a sink, over which is arranged a developing light. About five feet from the sink along one end of the room is the printing light. This light is mounted on a pine board attached to the edge of a shelf, 12 inches wide. On the lower edge of this board is a socket, into which is screwed a 32 candle-power incandescent bulb. The light is operated by a lever switch attached to the upper end of the board and within easy reach of the printer. This switch can be encased in a box with a slot cut on the top, and a door attached to the front, running the depth of the box. By allowing the handle of the switch to extend through the opening, the light may be turned off or on at will, without opening the door of the box. This box also prevents the possibility of getting an electric shock by taking hold of the switch except by the handle.
690. The light is arranged about 18 inches from the table, with a tin reflecting hood over it. This concentrates all the light, throwing it downward upon the printing frame. An important convenience of this printing light is the advantage one has of being able to dodge in the printing by holding the frame at any desired angle. By placing the box a certain distance from the light the printing may be done by laying the frame flat upon it. By means of the switch the current is turned off after each exposure, which effects a saving on electric light bills.
691. The developing light, which is a 16 candle-power incandescent, is encased in a bevel-shaped box, having a glass front, covered with one sheet of yellow post office paper. The bevel-shaped box permits the light to fall upon the print in the developer. It also supplies sufficient illumination to the room to permit loading the printing frame. By means of the cardboard partition between the printing and developing light, the developing and loading of the frame can be carried on while the paper is printing under the printing light, as one light will not interfere with the other.
692. The essential point is to provide for some simple way for uniformity of exposure to the light, as the slightest variation in the position of the printing frame in its relation to the light will make a difference in the time of exposure required for the best results. It is essential to have a perfectly even illumination over the entire surface of the negaiv-13 tive. In order to ascertain whether the light is evenly diffused at the point selected for exposure, take a piece of white cardboard the size of the printing frame. Hold it parallel to the source of light, moving it backward and forward over the box until you determine the location of the part where the illumination seems most even. Allow this to be the printing point. A good general rule is to measure the negative from corner to corner, diagonally, making that the distance for the first test. In most cases it will be a correct guide for printing.