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PART 2 Light: The Luminous Environment

A narrow wavelength band of electromagnetic radiation (from about 380 to 780 nm, as shown in Fig. 1.2) is perceived by our eyes as light.

2.1.1 Attributes of light

As for any other electromagnetic radiation, the velocity of light (c) is approximately 3 × 108 m/s (or 300 000 km/s). Its two main attributes are itsquantityand itsquality. Its quantitativeaspects are discussed in Section 2.1.3 (photometry). Its quality is characterised bywavelength (λ, inm) and its reciprocal, the frequency (f, in Hz). The product of these two always gives the velocity:

c = f × λ, (2.1)

so, if one is known, the other can be found by dividing the known one into the velocity

λ = 3 × 10 8

f or f = 3 × 10

λ .