Luminous efficacy

“ Production of Thermo-luminosity.—Certain bodies, such as fluorite, become luminous when heated; they are thermo-luminescent. Their luminosity disappears after some time, but the capacity of becoming luminous afresh through heat is restored to them by the action of a spark, and also by the action of radium. ”

“ Although two illuminants may be of the same luminous intensity, they may differ widely in actinic value. It is impossible to rate the different illuminants in a general manner as to actinic value because the various photochemical reactions are not affected to the same extent by rays of a given wave-length. Nearly all human eyes see visible rays in approximately the same manner, but the multitude of chemical reactions show a wide variation in sensitivity to the various rays. ”

“ All this time its luminous efficiency is increasing, because it is radiating not only an increasing percentage of visible radiant energy but an increasing amount of the most effective luminous energy. But even when it appears white, a large amount of the energy which it radiates is invisible infra-red and ultra-violet, which are ineffective in producing light, so at best the substance at this high temperature is inefficient as a light-producer. ”

“ How is it that the oxygen and hydrogen flame gives so little light, and with a solid body present, pours forth such a flood of brilliancy?
The production of artificial light by electrical and chemical agencies will necessarily find some consideration under their respective heads. There are numerous phenomena which connect themselves with luminous power, or appear to do so, which, in the present state of our knowledge, cannot come immediately under our attention. ”

“ An eventful feature in practical lighting is the proper scattering or diffusion of light, by shades, screens, and reflecting surfaces. We want to emulate the diffusion of daylight. It is marvelous how whitewashed surfaces do this. Well-selected globes act as though they were self-luminous; they scatter light and produce shadows. The power of the light, however, to penetrate fogs does not appear to be any greater than that of gaslight. ”

“ But when certain other substances, such as sulphate of quinine, or a thin slip of uranium glass, are placed in the path of the rays, this rapid motion is arrested and modified, and these rays, which in themselves are not luminous, are reflected back to our eyes as luminous rays. The rapidity of the vibrations being moderated, our retinas become sensible to them as rays of blue light. ”

“ We see then, that air (oxygen) , water, and some photogenic substance are necessary for the light production. Spallanzani's experiment, which has been confirmed for a great many luminous forms, shows also that animal luminescence is not a vital process, in the same sense that the conduction of a nerve impulse is a vital process. A nerve loses its characteristic property of conduction on drying or maceration while luminous cells still possess the power to luminesce after drying or maceration. ”

“ Those that exist beyond the red ray are capable of producing heat, while those that are beyond the violet excite chemical action. These invisible violet rays can be actually made perceptible to the eye, or, in other words, the undulations or waves proceeding from this end of the spectrum can be made to strike against certain substances and induce luminous vibrations, so as to connect the dark space beyond the violet with a brilliantly illuminated band. ”

“ There must be some radical departures if the efficiency of light-production is to reach a much higher figure. A good deal has been said of the firefly and of phosphorescence. These light-sources appear to emit only visible energy and, therefore, are efficient as radiators of luminous radiant energy. But much remains to be unearthed concerning them before they will be generally applicable to lighting. If ultra-violet radiation is allowed to impinge upon a phosphorescent material, it will glow with a considerable brightness but will be cool to the touch. ”

“ Heat and other conditions of the medium probably have a share in these operations of color. Still, the peculiar and powerful effect of luminous radiation as a part of them is beyond dispute.
The whole system of organic functions shares in the benefits of light. Darkness seems to favor the preponderance of the lymphatic system, a susceptibility to catarrh in the mucous membranes, flaccidity of the soft parts, swellings and distortions of the bony system, etc. Miners and workmen employed in ill-lighted shops are exposed to all these causes of physiological suffering. ”

“ Hence in the parts of the eye adapted to darkness we experience the faint brightness as strongly luminous, even dazzling, whereas in the parts more adapted to light we feel the same degree of brightness to be dark. That the action of the inner light is responsible for the differences becomes clear if, while the negative after-image is still visible, we darken the eye with the hollowed hands. Then at once in the dark field of vision the positive facsimile of the window appears, woven by the activity of the blood which reproduces the outer reality. ”

“ Luminous paint which, if exposed to the light during the day, will give off sufficient light at night time to enable one to see the time by a watch, may be had to last several years, if protected by a piece of glass from the weather, and it is extremely useful for certain positions where it is not desired to burn a light. ”

“ Two bright lights may be made to produce darkness.—If two pencils of light radiate from two spots very close to each other in such a manner that they cross each other at a given point, any object placed at that line of interference will be illuminated with the sum of the two luminous pencils. If we suppose those rays to move in waves, and the elevation of the wave to represent the maximum of luminous effect, then the two waves meeting, when they are both at the height of their undulation, will necessarily produce a spot of greater intensity. ”

“ In considering artificial light, we will avoid all efforts to analyze the different forms of energy, magnetic energy, electric energy, heat energy, mechanical momentum, radiating energy, and deal with result rather than with cause and effect. It will be sufficient to state as the deduction of the scientist that certain waves or vibrations which affect the fibers of the optic nerve are transmitted by the brain into color. (¶ 3.) Self-luminous bodies are bodies which produce light. ”

“ Intensely coloured bodies do make an impression upon perfectly blind men; and those who, being born blind, know no condition of light or colour, will point out a difference between strongly illuminated red and yellow media. When the eyes are closed we are sensible to luminous influence, and even to differences of colour. We must consequently infer that light produces some peculiar action upon the system of nerves in general; this may or may not be independent of the chemical agency of the solar radiations ”

“ The only explanation ever offered by competent authority of the luminous radiations from persons in disease, ascribes them to an efflux or escape of the nerve-force, which is known to be kindred in its nature to electricity, transmuting itself into luminosity as it leaves the body. The Seeress of Prevorst reported that she saw the nerves as shining threads, and even from the eyes of some persons rays of light seemed to her to flash continually. ”

“ Each of the luminous points is thus composed of a multitude of facets, and forms an apparatus entirely similar to that which Fresnel has invented for the diffusion of light, and which bears his name. When this corneous cap is removed, the luminous matter loses a great part of its brilliancy. Every thing, in other respects, is managed with a view to increase the light to the utmost. ”

“ White as well as black paper is charred and ignites in it. A piece of platinum-foil is raised to white heat in the dark focus. If we examine the incandescent platinum with a prism, we find that it emits again all colors, from the most extreme red to the most extreme violet; consequently, we have here the counterpart of fluorescence. The dark rays, by the augmentation of the number of vibrations, are converted into luminous ones, influencing the eye. ”

“ Shadow is the absence of light, merely the obstruction of the luminous rays by an opaque body. Shadow is of the nature of darkness. Light [on an object] is of the nature of a luminous body; one conceals and the other reveals. They are always associated and inseparable from all objects. But shadow is a more powerful agent than light, for it can impede and entirely deprive bodies of their light, while light can never entirely expel shadow from a body, that is from an opaque body. ”

“ A single and distinct luminous body causes stronger relief in the object than a diffused light; as may be seen by comparing one side of a landscape illuminated by the sun, and one overshadowed by clouds, and so illuminated only by the diffused light of the atmosphere. ”

“ Attracted by some potent charm toward this dazzling focus, they come inquisitive and ardent, to warm themselves at its furnace. At first pale and feeble, they are born again when the Sun caresses them with his fervid heat. Their motions accelerate, they haste to plunge wholly into the radiant light. At length they burst out luminous and superb, when the day-star penetrates them with his burning splendor, illuminates them with a marvelous radiance, and crowns them with glory. ”

“ The azure vault of the firmament crowns the Earth with a dome of dazzling light. The fires of the orb of day shed their beneficent influence generally upon the world.
Yet, see! The radiance diminishes. The luminous disk of the Sun is gradually corroded. Another disk, as black as ink, creeps in front of it, and little by little invades it entirely. The atmosphere takes on a wan, sepulchral hue; astonished nature is hushed in profound silence; an immense veil of sadness spreads over the world. Night comes on suddenly, and the stars shine out in the Heavens. ”

“ No small hole can so modify the convergence of rays of light as to prevent, at a long distance, the transmission of the true form of the luminous body causing them. ”

“ There is nothing more profound, more mysterious, more fertile, more gloomy, or more dazzling, than a window lighted by a candle. What we can see in the sunlight is always less interesting than what goes on behind the panes of a window. In that dark or luminous hollow, life lives, life dreams, life suffers. ”

“ The world, with its joys and its sorrows, no longer exists for them; they live in light, in fire,—they are salamanders, phœnixes, freed from all weight, light as flame, burning themselves out, rising again from their ashes, always luminous, always ardent, invulnerable, invincible. ”

“ Can there be any one upon the Earth who has not been struck by the phosphorescent lights that glide through the somber night, leaving a brilliant silver or golden track—the luminous, ephemeral trail of a meteor?
Sometimes, when Night has silently spread the immensity of her wings above the weary Earth, a shining speck is seen to detach itself in the shades of evening from the starry vault, shooting lightly through the constellations to lose itself in the infinitude of space. ”

“ The source of light must be so placed that it will not strike the eyes directly. Care must be taken that there are no surfaces reflecting light directly into the eyes. The lighting system must provide illumination of sufficient intensity, yet without a glare which produces eye strain. While our modern methods of artificially producing light are a great boon to civilization, they may also be a great detriment to health to say nothing of the discomfort that is caused by improper methods of lighting our homes, schools, and workshops. ”

“ So much energy is wasted in the production of heat-waves and ultra-violet waves which we do not want, that 90 per cent. or more of the power used in illumination is wasted. Would that the glow-worm, or even the dead herring, would yield us its secret! Phosphorus is the one thing we know as yet that suits the purpose, and—it smells! Indeed, our artificial light is not only extravagant in cost, but often poor in colour. The unwary person often buys a garment by artificial light, and is disgusted next morning to find in it a colour which is not wanted. ”

“ It goes without saying that if there were simply health-giving qualities in the blue rays and no injurious ones in the red and yellow, ordinary light would be as effective as that which had passed through blue glass; for the glass introduces no new quality or color into the light; it only absorbs certain rays of the spectrum, allowing others to pass. ”

“ In providing artificial light for our buildings the laws of the physical organ of sight must be considered. However, the question of lighting is not alone one of artificial production of light in our buildings, but also deals with proper admission of natural light from natural sources. ”

“ You will find that most out-of-door effects are produced by soft natural lighting which gives a sense of distance and perspective to the scene. For this effect use yellow, amber, and white lights with an occasional blue or red. Only lights coming from several directions will produce the subtle tones of nature. This means using footlights with discretion, stronger lights overhead, and placing strips wherever you need them in order to destroy the shadows which other lights may throw. Sometimes it takes several hours of experimenting to find the right lighting for a single scene. ”

“ If you want a really brilliant, clear, white light, you must trim the lamp yourself. A small piece of pale blue or neutral-tint glass, interposed between the lamp and the microscope, has a wonderful effect in diminishing the yellow hue which belongs more or less to all artificial lights which are produced by the combustion of oil or fat. We have no doubt but that in a few years we shall be rid of the clumsy and dirty machines that we call lamps, and have substituted for them the pure brilliancy of the electric light. ”