In the case of such illuminants as acetylene or limelight {85} care must be taken that they are turned fully on before centering, otherwise turning on the fuller amount afterwards will raise the position of the luminous spot.
It is not the intention of the author to give precise working instruction for all and every variety of the above illuminants as manufactured by different firms.
Modern illuminants have luminous efficiencies ranging from 5 to 30 lumens per watt, so it is seen that much is to be done before the limiting efficiencies are reached.
Although two illuminantsmay be of the same luminous intensity, they may differ widely in actinic value.
Artificial light in the home symbolizes independence of nature and protection from the elements and there is a firm desire to counteract the increasing whiteness of modern illuminants by means of shades of a warm tint.
The nearer ultra-violet rays are found in sunlight and in most artificial illuminants and are transmitted by ordinary glass.
Thus the high efficiency of the modern illuminants is utilized to advantage even though their color is maintained the same as the old illuminants.
Doubtless the future will see the production of efficient light of many qualities or colors, but to-day many of the demands must be met by modifying the artificial illuminants which are available.
The proportion of these is controlled in so far as possible in order to obtain illuminating value and some of them are reduced to very small percentages because they are valueless as illuminants or even harmful.
Although in lighting little use has been made of the injection of chemical salts into ordinary flames, it appears certain that such developments would have risen if electric illuminants had not entered the field.
Old illuminants such as that emitted by the candle and oil-lamp were used for centuries in interiors.
The "vacuum" tube affords a possibility of an extensive variety of illuminants differing widely in spectral character or color.
Of course, no illuminants are available which approach this theoretical ideal and it is not likely that this would be a practical ideal.
In general, it may be said that the arc-lamps including the mercury-arcs provide the most activeilluminants for photochemical processes; however, a large number of electric incandescent filament lamps are used in photographic work.
By using various substances besides carbon for the electrodes, illuminants differing in spectral character can be obtained.
There is one respect in which acetylene and other flame illuminantsare superior to electric lighting, viz.
Likewise where storage accommodation is limited, as in vehicles or in ships or lighthouses, calcium carbide may be preferable to oil or other illuminants as a source of light.
Figures showing the ratio of the visible light emitted by various illuminants to the amount of energy expended in producing the light and also the energy equivalent of each spherical Hefner unit evolved have been published by H.
This higher light-yielding capacity of calcium carbide, ready to be developed through acetylene, gives the latter gas a great advantage over all other illuminants in respect of compactness for transport or storage.
For lighthouse purposes other gaseous illuminants than coal gas are as a rule more convenient and economical, and give better results with incandescent mantles.
Other illuminants are also in use to a considerable extent.
Coal gas and electricity are also used as illuminants for port lights when local supplies are available.
The quantities of these compounds emitted from different illuminants for every candle of light per hour will be seen from the following table: Cubic Feet per Candle Illuminant.
In the opinion of the insurance companies "the electric light is the safest of all illuminants and is preferable to any others when the installation has been thoroughly well put up.
When made for illuminating purposes it must be enriched, that is, illuminants must be added, since both carbon monoxide and hydrogen burn with non-luminous flames.
Because the arc lamp is the cheapest of all illuminants it is adopted for out-of-door lighting where its unpleasant glare is tempered by distance.
From a brief consideration of illuminants let us pass to a rapid survey of a most important group of structural materials, the steels.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "illuminants" in a variety of sentences. We hope that you will now be able to make sentences using this word.
