PHOTOGRAPHY BASIC LIGHT
What is light?
For photographers to work successfully with light they need to understand its composition and the basic rules it follows. This section looks at colour theory, at how to measure light for correct exposure, how to filter lights,and imaging at the ends of the visible spectrum.
Photographic daylight has a special meaning and is
not what people presume. Natural light varies
immensely in quality depending on the time of day, the
season of the year and the location.
This is lights – not necessarily natural – that is around us
all the time and available for making images. Available
light photographers often work with low levels of light
but capture some of the most evocative images.
Lights specifically generated for photographic use
comes in continuous form, from tungsten or
fluorescent lamps, for example, or as a high-energy
flash. This section looks at the alternatives and their
pros and cons.
Studios can be thought of as an unlit box into which
the photographer brings every light source and
controls every reflection and shadow. Here we look at
how simple lighting is adjusted and controlled and how
complex lighting is built on first principles.
Quality of light has a strong expressive component;
this section looks at how a technical understanding
can be used to fuel creativity. The section also looks at
some ways of imaging without a camera.
Lights is that narrow band of electromagnetic radiation to which the human eye is
sensitive. There are no exact boundaries to the range of visible lights, as individuals differ.
Typically, our eyes are receptive to a range of wavelengths of light between 400–700
nanometres (nm). (A nanometre is one millionth of a millimetre.)
Light has three physical properties that interest the photographer – amplitude (or intensity), the
wavelength or frequency and the angle of vibration (or polarization). In layman’s terms, intensity
can be thought of as the brightness of light and the frequency or wavelength determines its
colour; we can barely perceive changes in polarization but this phenomenon can be
manipulated photographically with polarizing filters. These are covered in a later section.
Light travels in straight lines, which is why we get shadows. It is also reflected off a mirror or
silvered surface at the reverse angle to which it falls, like a billiard ball hitting a cushion.
Knowledge of these simple facts allows photographers to shape light using cutters and
reflectors. Light can also be bent (refracted), which means we can design lenses to
Without light, there are no colours. A green pepper only looks green if the corresponding
wavelengths (colours) are present in the illuminating light. In orange light that contains no
green, a green pepper will look grey and colourless.
‘Light is our paint brush and it is a most willing tool in the hands
of the one who studies it with sufficient care.’
Laura Gilpin (American landscape photographer)
We are familiar with the range of colours within the spectrum that exists between 400–700nm
as the colours of the rainbow (red, orange, yellow, green, blue and violet – modern science no
longer counts indigo as a usefully separate colour). The colours of the rainbow are what you
see when a beam of light cuts through the edge of a drinking glass. This is exactly what
happens in the controlled conditions of the physics laboratory using a prism of glass to create
the coloured bands of the spectrum by bending (refracting) white light. The rainbow colours
are spread out because different wavelengths (colours) of light move at different speeds
through the denser glass. This simple observation is vital to accurate lens design as it is the
source of colour fringes in images from less than perfect lenses. We need to understand the
spectrum to know how to use filters.
filter glass or plastics device that modifies light passing through the camera lens. Computer software module
that applies an image effect
white light equal blend of all colours in visible spectrum
The inverse square law
The inverse square law states that the intensity of lights observed from a constant source falls
off as the square of the distance from the source.
Any light source that spreads its lights in all directions obeys this law. In the real world, this is
why it gets dark so quickly as you move away from the campfire!
Put simply, the inverse square law means that as you double the distance from the light you
quarter the light intensity. In fact, the lights falls off as 1 over (inverse) the distance multiplied by
itself (squared). The light measured at 2 metres from a light source will be 1/22 or 1/4 the
intensity at 1 metre. The lights measured at 4 metres from the same source will be 1/42 or
1/16th the intensity at 1 metre.
Photographically speaking, as every stop means a halving or doubling of light, 1/4 the amount
of light is 2 stops down; 1/16th of the light is 4 stops down. Therefore, a light meter reading
f/16 at 1 metre, for example, would read f/8 at 2 metres and would read f/4 at 4 metres.
It is important to understand this law, as it is one of the main ways in which light intensity can
be controlled in the studio. The only light source that does not obey this law is the sun – as any
distance we move something on earth is trivial compared to the distance from the earth to the sun.
White light and primary colours RGB
White light passing through a prism creates all the colours of the rainbow, but only three of
these colours are necessary to make up all the others. These are called the additive primary
colours – red, green and blue – familiar from the ‘RGB’ label used in TV, computer monitor and
video ‘speak’. Add equal quantities of red, green and blue light to make white.
Subtractive colour mixing
Subtract any one of these colours – red, green or blue – from white light and you are left with a
combination of the remaining primaries. The colours from the remaining combinations – cyan,
magenta and yellow – are the so-called subtractive primaries. RGB is the additive world of
light and of the digital sensor; CMY is the world of reflected light, where these colours are used
as dyes or pigments in our inks on white paper or as chemical dyes in film, to act as filters on
white light to create the range of visible colours. Add equal quantities of cyan, magenta and
yellow inks and you get black.*
* True black is added in four-colour (CMYK) printing, as real-world ink pigments are not pure
enough to give black, instead giving a dirty purple-brown.