Light & Vision

Colour temperature determines the character of light and also how illuminated colours are emphasized. If the colour temperature is low, we perceive the light as a warm glowing light, with a red colouring. Higher colour temperature gives us colder light, which explains why fluorescent lamps, with high colour temperature, has a light that we perceive as cold whereas standard light bulbs are perceived as warmer.

The luminous intensity is the most commonly used measurement for light and part of the reason is that it easy to quantify. Lux can be written as lumen per square meter, and helps explain how luminous flux of a light source hits a specific surface. For indoor work, a luminous intensity of 500 up to a 1000 lux is common. In our homes, the intensity is often around 200 lux. These numbers pale in comparison to the luminous intensity on a sunny day, which can exceed 100 000 lux!

Candela is the measurement of light brightness in a certain direction. Knowledge of the Candela of a light source allows us to calculate how much light will reach a specific surface. The luminous intensity of a light source decreases by a factor that is the square of the distance.

To measure the ability of the source of light to render surrounding colours and our product exposures, rendering average (Ra) is used. On a scale from 0 to 100, a rendering average of 100 represents perfect colour rendering and a zero represents a light source that cannot render anything but grey tones. A Ra of at least 80 is recommended for environments frequented daily by humans.

This is a property of light that more and more people are aware of when choosing which type of light source to use. It measures how effectively a lamp uses the supplied energy (watt). An effective light source will turn the supplied energy to light, while a more ineffective one will turn it into heat.

Visible light is in the wavelength 400 – 780 nm, where one nanometer (nm) represents one billionth of a meter. In this short interval we have the entire spectrum of colours. If the wavelength exceeds 780 nm, visible light turns in to heat radiation, infrared light. If light has shorter wavelength than 400 nm, it is ultraviolet radiation, which may be harmful.

If we continue to shorten wavelengths, we get x-rays, gamma rays and cosmic radiation. If we increase wavelengths past infrared light, we get the wavelengths used for radar surveillance, radio and TV.