54 | New Scientist | 19 October 2019
In the ink
Why do blue highlighter markers
never seem to have the high
luminosity of pink, yellow, orange
and light green highlighters?Guy Cox
Sydney, New South Wales, Australia
There are two reasons for this.
One is that our eyes are much
less sensitive to blue light – peak
sensitivity is in the yellow-green
region of the spectrum, so if all
markers were of equal intensity,
the yellow and green ones
would always seem brighter to
us. Sensitivity falls in the red
region, too, so red markers can
never match the brightness of
yellows and greens either.
The second reason is inherent
in the way these markers work.
They seem so bright because they
contain fluorescent dyes that
absorb short-wavelength light
and re-emit it at their specific
colour. Blue is at the short end
of the visible spectrum, so a blue
fluorescent pigment can only be
excited by ultraviolet light, which
is usually in short supply indoors.
Yellow-green dyes can be
excited by blue light and UV, so
they are excited more efficiently.
Red-emitting dyes can be excited
by green light as well and this
helps to compensate for the eye’s
lower sensitivity to their colour.Eric Kvaalen
Les Essarts-le-Roi, France
Our eyes are more sensitive
to light in the middle of the
spectrum, which means orange,
yellow and green. For longer
wavelengths (red) or shorter
wavelengths (blue), the sensitivity
drops off, falling to zero for
infrared and ultraviolet.
Pink is a mixture of red and
white, which makes it more
luminous than just red. One can
also make a mixture of blue and
white, which will also be fairly
luminous. Some languages, such
as Russian and Hebrew, have a
different word for this blue/white
mixture, just as we have different
words for pink and red.Good consumers
Which is better for the environment,
online shopping or traditional high
street shopping?Brian Horton
West Launceston,
Tasmania, Australia
In terms of packaging and
shipping, it is more efficient
for a shop to bring large quantities
of goods from a factory or depot
to your local area than for
everyone to buy those goods
online and have them delivered
individually to their homes from
the factory or the depot.
Therefore, if the items you want
are readily available from local
shops, then in environmental
terms, it is better to buy them
locally. For anything else, buying
online would be more efficient.
We can probably ignore the
environmental cost of driving to
the shops to buy goods, since this
is roughly equivalent to the cost of
the final stage of delivery to your
house when you buy online.Simon Dales
Oxford, UK
I would say the best options are
to drive to an out-of-town store
to do your weekly grocery shop,
ideally when driving back from
somewhere else. Then go to a
local store for perishables. And
for most of the rest, walk, cycle
or use public transport.Hillary Shaw
Newport, Shropshire, UK
There are factors other than
emissions used in transporting
goods to consider.
Online searches themselves
use energy. Car owners who shop
online may drive elsewhere in the
time freed up from shopping. But
trip-linking may mean going to
the shops is done in conjunction
with, say, work journeys, and then
there is no gain by going online.With set delivery slots, a vehicle
bringing goods ordered online
may not take the shortest route,
and with frequent stop-starting its
fuel use may be higher than that of
consumers driving to a shop. The
distance from factory to online
delivery depot may also be long.
Socially, traditional high street
shopping wins hands down: you
retain more employment, meet
more people, keep town centres
viable and enjoy experiences
outside the home. If only the
roads weren’t so clogged and
the parking so expensive.Ali El Idrissi
San Francisco, California, US
Rather than just choose between
online or high street shopping,
society needs to transition to
sustainable consumption and
organise new ways to provide
everyday products and services.
The consumerist culture
associated with shopping – both
on- and offline – has huge negative
impacts on our health and our
environment. Humanity currently
uses resources each year equal to
those of 1.7 planets. If nothing
changes, this will be two planets
by 2030. A study in the Journal of
Industrial Ecology calculated that,
in 2007, household consumption,
including shopping, contributed
to more than 60 per cent of carbon
emissions. This is unsustainable.
There is nothing wrong with
consumption per se. It is part
of our lives, reflects our journey
and carries our memories. The
problem is the excess that
happens when consumption
itself becomes the goal. ❚For more on this subject, see
“The last-mile revolution”, New
Scientist, 7 September, p 42 – EdThis week’s new questions
Shrinking gravity The first law of thermodynamics is the
conservation of energy. The first law of geology is that rocks
fall downhill. Falling rocks gain energy. The energy must
come from gravity. So why doesn’t gravity get less every day?
Anthony Woodward, Portland, Oregon, USSuper seers I have heard that it is possible for some people to
see ultraviolet light. Is this true, and if so, how is it possible?
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IMAGEBROKER/ALAMY STOCK PHOTOSince its force gives energy
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