B+W 1057404 Datasheet download pdf (Page 4)

LIGHT, COLOR , FILT ER EFFEC T S

Light, wavelength and color

Light is an electromagnetic phenomenon with many

facets. It travels with unimaginable high speed and it

transports energy – even through completely empty

space. Light can traverse “transparent” materials and

in the process be diverted from its straight path, be

reflected diffusely or directly, be absorbed and a

blend of frequencies can be altered through absorp-

tion yielding a new balance of color. Light has fasci-

nated generations of physicists and enabled astrono-

mers to discover the secrets of outer space at dis-

tances that are far beyond our reach and our capac-

ity of imagination. Light is the medium with which we

“create ourselves a picture”.

The nature of light is so complex that we require

two different physical models in order to explain its

qualities that sometimes appear to be contradictory.

When reacting with matter, light can behave as if it

consisted of tiny particles (“photons”) that zip

through space and which upon impact produce a

“photo effect” reaction, which is the basis of the

function of an exposure meter or digital camera sen-

sor. However, it also behaves like a wave phenome-

non that spreads in space in a spherical manner, con-

sisting of interwoven electrical and magnetic fields

that vibrate at right angles to each other. The num-

ber of these vibrations per second (on the order of

600,000,000,000,000) is just as unimaginable as the

spreading speed of light (nearly 300,000 km or

¡86,4¡¡ miles per second). We are able to visualize

the wavelengths of these vibrations: circa 380 nm to

750 nm (nanometers), or approximately ¡/2000 of a

millimeter. We perceive the different wavelengths as

different colors: the shortest ones as violet, then

blue, green, yellow, orange, red and the longest wave-

lengths as purple-red. And white light is nothing

more than an even mixture of all these colors in the

same proportion as we receive it from the sun.

Reflection properties define the color of an object

An object that is struck by light can reflect that light

(nearly) completely, partially or (nearly) not at all. If it

reflects all the wavelengths, i.e. colors, uniformly and

nearly completely, the object appears to us as white.

If it reflects them uniformly but only partially, the

object will appear to us as gray under white light, and

when it reflects hardly anything, we perceive it as

being black. Most objects, however, do not reflect all

colors uniformly, some of them are reflected more

strongly, others less strongly or not at all. The sur-

face of the object will then no longer appear to us as

being white or neutral gray, but colored, usually in a

“mixed color”.

Additive and subtractive color mixig

A spread of the various component colors of white

(or any) light is called its spectrum. In nature, we can

see a spectrum in the form of a rainbow. Rainbow

colors are pure colors, because each color can be

defined by a specific wavelength. On the other hand,

an object that appears green, for example, does not

necessarily reflect just one wavelength or of a nar-

row band of wavelengths. It also may absorb a variety

of frequencies, significantly blue and red. It reflects

the remaining spectral colors, this mixture of which

is perceived by us as that shade of green. If we re-

plenish this mixture of colors with the missing shade

of magenta, we will once again see white. Such op-

posite colors, when combined form white, are called

complementary colors. Other examples are yellow

and blue or red and cyan.

When light of one color is added to light of an-

other color, this is called “additive color mixing”. As

an example, this is the case when a red spotlight and

a green spotlight illuminate a stage and we see yellow

light as the combined (= added) color where the two

spotlights overlap. But if we mix colored pigments,

or if we paint or print colors over each other, some-

thing different happens: each colored pigment ab-

sorbs the part that is complementary to its own col-

Red

Cyan

Magenta

Blue

Yellow

Green

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B+W 1057404 Datasheet Page 4

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