Art of Lighting

Light forms part of the so-called Electromagnetic Spectrum comprising among others Radio and TV signals, Infrared and Ultraviolet radiation, X-rays, nuclear and cosmic radiation. Of these, only Light waves are useful for animals and humans to see with.

The spectrum also includes the standard 50Hz AC current (with wave length 6000 Kilometers) and visible part with wavelengths 780-380 nanometer (=10-9 metre!)

Different wavelengths give a different variety co lour impressions to the eye from Red, Orange,Yellow, Green , Blue, Indigo to Violet.The spectrum of electromagnetic radiation.

Propagation of Light

When Light strikes a surface, part of it is reflected, part absorbed and part transmitted. Reflection can be like a mirror or diffuse like a painted surface. Absorption is usually converted into heat. Whatever is not reflected or absorbed is let through as transmission.

The optical design of lamps and luminaries apply the above methods of light propagation to create the desired effects.

Reflection, Absorption and Transmission

The Human Eye

The human eye is spherical in shape with a diameter of 25 millimeters. Its positioning muscles allow it to swivel in any direction. Superficially, the eye resembles a camera with a Lens, which throws a reduced upside-down image of a distant object onto the light-sensitive back surface called the Retina.

Cross-section through the right eye, seen from above.Within the visible range, eye sensitivity varies strongly with wavelengths. For example, under well lighted conditions (photo vision), the eye is about 20 times more sensitive for light with a wavelength 550 nm,than for red or blue. The peak sensitivity for low lighting levels becomes about 50 nm nearer to the blue end of the spectrum.

Standard spectral eye-sensitivity curves for photo V and isotopic V' vision, according to CIE.Relationship between eye performance and lighting criteria

Finally, the requirements for comfortable working under light are dependent on the following:-

Amount of Lighting,
Luminance or brightness,
Distribution in the field of view,
glare negletion,
Distribution of light in the space,
Light colour and Colour rendering.

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