To be comfortable inside our buildings, we need to have light.
At least, enough light.
But it isn't just the quantity which matters, it is also the quality.
And not all lighting is alike,
especially for bringing out the subtleties of certain areas, particularly rich in color.
Like this Parisian apartment,
transformed into a huge art piece by street artists.
And in order to understand what makes the quality of light,
we need to fully understand what light is.
Light is the superposition of electromagnetic waves,
each of them possess a specific wave length.
The wave lengths that our eyes can see are quite limited:
They only range from 400 nm, that is for violet light,
to 800 nm, that is for red.
But visible light only represents a very small part of electromagnetic waves.
There are a lot of others, which possess various wave lengths
and which our eyes cannot detect:
There are the ultraviolets and infrareds of course,
but also the microwaves,
the radio waves,
the gamma rays,
and the x-rays.
To detect these light waves,
our eyes have a system which is ultimately rather rudimentary.
It has 4 types of sensors :
There are the rods, which function when it is dark and which cannot distinguish colors.
And the cones, there are three types.
The "blue" cones, which detect blue and violet light,
the "green" cones for green and yellow.
And the "red" cones which detect anything from yellow to red.
But the cones cannot measure the wave length of the light waves they are receiving,
they are just stimulated or not,
depending if the light is within the range of their sensitivity.
Let's imagine that I shine a yellow light to you :
your red cones and green cones will be stimulated.
Now, at the same time, if I send you a red light and a green one at the same time,
the same cones will be stimulated in the same way,
and your eyes will be unable to make the difference from the preceding situation.
And for that reason when we mix red and green light,
we get a yellow light.
The light coming from the sun, seems to us to be white or yellow.
But in reality, and we can clearly see this when there is a rainbow,
it is made up of all the visible wave lengths,
plus ultraviolets and a great deal of infrareds.
and it is precisely because it contains all the wave lengths,
that natural light is so efficient
in rendering the colors of areas or the objects that surround us.
Incandescent light bulb functions somewhat on the same principle :
But since the filament temperature, about 3,000°C,
is much lower than that of the sun, 6,000°C,
the composition of the wave lengths will be different.
First, the light from an incandescent bulb will appear more yellow than the sun.
But above all, it is composed of infrareds, for the most part,
which are rays, which warm but don't light up.
That means that an incandescent bulb,
is, in a sense, an electric radiator,
which, on the side provides a little bit of light.
From an energy standpoint, it's not so great.
To replace incandescent bulbs,
we have dreamed up new lighting technologies,
more economical and long-lasting.
Like for example, the fluorescent lamps,
the LEDs,
or even neon tubes,
which, contrary to what their name indicates, don't have any neon!
That which we improperly call neon tubes,
function on the same principle as the fluorescent bulbs.
They contain mercury
which when activated by an electrical discharge, will emit ultraviolets.
Which then are converted to visible light
by means of the white powder applied to the interior surface of the tube.
The drawback of neon tubes,
is that they don't render the colors as well
as the sunlight or incandescent bulbs.
That is due to the fact that the light they emit
is much less homogenous on the various wave lengths.
And it is also the principle of these discharge lamps
that we are using now during this shoot.
In order to understand this phenomenon of color rendering,
we can have fun by exaggerating it.
Here I have a nice table, full of colored tiles.
In daylight, we can easily distinguish all the shades of color.
And now, if I get under an artifical light,
with which I have fun by varying the composition,
we can't distinguish all the colors anymore.
The shades of color are completely washed out.
To quantify this phenomen, we talk about a color rendering index.
This index is rated at 100 for sunlight
or that from a good incandescent lamp.
For a cheap neon tube only 50.
And up to 90 for the best ones.
And for sodium lamps,
you know these are lamps found in highway tunnels :
The color rendering index is only 20.
And that's why under these lights, everything appears totally yellow.
For some time, now,
we have seen the development of new lighting technologies
based on electro-luminescent diodes :
Such as LEDs.
The principle of LEDs is generally the opposite of the photo-voltaic panel :
They are made with semi-conductor material.
Which will convert electrical energy into photons.
And the color of the transmitted light depends on the material used.
The first LEDs were developed in the 1960s,
from a mixture of arsenide and gallium phosphate.
And the light obtained was red.
Little by little, with the development of new materials,
they were able to make LEDs that emitted yellow,
then green.
With just red, yellow and green,
we've seen that they can't create quality lighting,
because it would be impossible to render all the colors' richeness,
like that which we see in these frescos.
Fortunately for the LEDs,
the deciding development took place in the 1990s,
with the discovery of the blue LEDs,
which gave their 3 Japanese inventors
the Nobel prize for physics in 2014.
The blue LEDs have been a revolution,
because these now permit the development of LED lighting
which is truly white,
that is, which contains more or less all the visible wave lengths.
The best white LEDs
today have a color rendering index of 98,
that is nearly as good as a natural light.
For the last few years, we have seen a new type of lighting on the market :
the OLEDs.
They function according to the same principle as the LEDs,
but with organic material,
hence the "O".
But above all they aren't point light sources anymore, but plane sources.
These OLEDs are still rare for lighting,
but you may have already seen them used in cell phones or TV screens.
OLED lamps like these, are sctually large pixels.
It will still take a few more years,
but we will see more and more OLED lighting coming into use
and potentially transform any surface into a lamp.
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