be as effective in that task as a small, narrow-beam
spotlight. The source used in the spotlight may well
have a much lower efficiency, but if it puts all of its
light only where we want it to be, it is likely to be the
most effective solution.
The experienced designer may prioritise the efficacy
of the whole installed design over the simplistic and
contextless quantification of the efficiency of the light
sources used in the design. In this way, real energy
efficiency is achieved through the use of effective
light – only using light where it is needed, when it is
needed and only for the intended purpose. Effective
lighting design appreciates the contribution that each
individual source of light makes to the whole three-dimensional composition. As architect Louis Khan
said, ‘even a space intended to be dark should have just
enough light from some mysterious opening to tell
us how dark it really is’. Thinking about the contrast
between effective and efficient lighting begins to cut
to the core of what it means to be a lighting designer.
It begins to remove the fog that surrounds that most
thorny of questions: what is lighting for?
If architectural lighting exists simply to allow people to
see, then maximising visual acuity seems like the most
sensible action. As is explained in countless textbooks,
visual acuity is broadly proportional to the quantity of
illuminance in the scene. So, within the boundaries of
comfortable viewing conditions (in other words, not
excessively bright), more light means better vision.
Even in the Renaissance, this was clear. Leonardo da
Vinci said, ‘since we see that the quality of colour is
revealed by means of light, it is to be deduced that
where there is more light will be seen more of the true
quality of the illuminated colour’.
This empirical knowledge about light appears to
support a quantified engineering approach that has
illuminance levels as its main preoccupation. But what
about the quality of light? What about the direction of
light? What are the qualities of the shadows created;
the brilliance of shafts of sunlight; the subtle colour
shifts between sunlight and skylight; the contrast?
All the many aspects of a natural scene that inspire
us deeply and bring joy to our eyes are the kinds of ▼
‘I can rationalise a design
approach based upon its
similarity or divergence
from natural lighting’