In actual practice an orthochromatic mixture of frequencies is used to give a black, gray and white picture.
"The Airlords of Han" by Philip Francis Nowlan
Orthochromatic photography discovered by Vogel.
"Coal" by Raphael Meldola
On the few occasions when orthochromatic plates are used the lamp need not be lighted.
"Photographs of Nebulæ and Clusters" by James Edward Keeler
Orthochromatic results exhibited by Dixon and Sons at the photographic exhibition in October.
"The Evolution of Photography" by John Werge