To understand the answer to this question fully you will first have to learn what light is, and particularly that it is not the flame from the gas jet or of the lamp or candle that is actually the light, but that light consists of rays or waves in the ether, which is constantly in all space and even in our bodies, coming from the something that is burning. This in the instance above mentioned would be the gas burning as it comes out of the gas jet, the oil in the lamp as it comes up through the wick or the flame of the candle. We are apt to call a lighted gas jet a lamp, or a candle, light, because it is steady. Really, however, there is no such thing as keeping light in a room in an actual sense, for rays of light travel from the substance which produces them faster than anything else we know of in the world. The first thing a light wave does when it is once created is to go some place, and it does this at the rate of 186,000 miles per second. If it cannot penetrate the walls of the room it is either reflected back in the direction from which it came or transformed by the objects which it strikes into some other kind of energy. When you look at the rays coming from a gas jet, you do not see one ray for more than, say the millionth part of a second, but because these rays of light come so fast one after the other from the burning jet and spread in all directions, they seem to be continuous. So you see that the rays of light are going away as fast as they are coming from the gas jet. They either go on as light or, as said above, are changed into other forms of energy when they strike things they cannot penetrate in the form of light, or rather one thing, which is heat. A large part of it goes into the air in the room in the form of heat, as you well know, now that it is called to your attention. Some of it goes into the furniture and some of it is changed into another form of heat, which, combining with the chemicals in other things it mixes with, changes their appearance and usefulness. As, for instance, the carpets and hangings in the room, the colors of which become faded when exposed to light rays too much. The heat from the light rays is responsible for the fading of colors in our garments as well. When you “put out the light,” as we say, or turn off the gas, you cut off the source of light. Really, then, our expression that “the light goes out” is only true while the gas is lighted, for from the flaming gas jet the light is going out all the time, whereas when the gas is turned off no light is being produced, and when you turn off the gas you do not turn out the light, but only that which makes light. Why Does a Fire Go Out?