New Scientist - 19.10.2019

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 – Ed

This 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, US

Super 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?

Kevin Burton, Buenos Aires, Argentina

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Since its force gives energy

to falling rocks, why doesn’t

gravity diminish over time?