Solid-state dark room light

Light-emitting diodes are perfectly suitable for dark-room light, because they (a) obviate the need of filters; (b) emit cold light; (c) have a life that is not shortened by continuous on-off switching; and (d) do not radiate infra-rays. The types used must, of course, have a high light output; for- tunately, there are nowadays LEDs with a luminous intensity of hundreds of millicandela. The sensitivity of photographic paper lies between wavelengths 300 nm and about 550 nm, whereas the wavelength of the light emitted by green LEDs is about 565 nm; that by amber types around 585 nm; and that by red LEDs about 640 nm. From this, it is clear that all three types of LED may be used with impunity. Nonetheless,inpractice,itisbest not to use green ones. Because of the special composition and high sensi- tivity of colour negative paper, only yellow LEDs with reduced light out- put should be used when processing this paper. The proposed light, therefore, has provision for reducing the emitt...