Story: Light

Page 2. Scientific observation

All images & media in this story

Factors affecting light

The clarity of New Zealand light is a widespread perception, but is it real? There is no absolute answer. The light varies with the weather, the season, the time of the day, and the place. Its quality is also affected by pollution in the atmosphere, which scatters and absorbs it. However, certain conditions contribute to low pollution and therefore clarity of light:

  • New Zealand’s distance from major industrial countries
  • low level of coal-burning
  • constant cleansing winds.

The proximity of the sea, which reflects sunlight, may also be a factor.

Measuring visibility

In places such as South Canterbury and Central Otago, which are protected from the rain by the Southern Alps, the air is exceptionally dry and clear. At the National Institute of Water and Atmospheric Research station in Lauder, Central Otago, researchers have examined both the meteorological visibility index (which measures contrasts of black and white over distance), and optical depth (which measures the absorption of light from the sun).

Findings

The air quality is high, with indicators (carbon monoxide, sulfur dioxide and nitrogen dioxide) typical of very clean southern maritime air. Air clarity, or visibility, is especially high because clouds and precipitation over mountain ranges upwind of the site wash the salt and other aerosols out of the air as it passes. Measurements at Lauder show that New Zealand air, along with that of Antarctica, is among the clearest on the globe.

An observatory such as Mt John, near Lake Tekapo, is regarded internationally as a superb site for looking at the stars.

Smoke signals

Although Central Otago normally has an exceptionally clear atmosphere, researchers at Lauder in the region note the impact of distant events. The 1991 Mt Pinatubo eruption in the Philippines, the 2001 Boxing Day bush fires in Australia, and an annual springtime burning of savannah and cropland in southern Africa, South America, southern Asia and Australia have all been observed at Lauder.

Pollution and fog

Most New Zealanders live in cities, where motor-vehicle emissions, domestic fires for heating and industrial discharges pollute the atmosphere. Christchurch has its smog alerts. And anywhere in New Zealand when the cloud cover comes down, ‘bad light’ can stop play in a cricket game, or fog can close airports.

Ultraviolet light

New Zealand receives comparatively high levels of ultraviolet light – a part of the electromagnetic spectrum invisible to the human eye. One reason is the clarity of the air surrounding the country. As a result of these higher levels, there are high rates of skin cancer, prompting a constant message in summer about the dangers of sunburn. In addition, paint, textiles and plastics deteriorate rapidly, and there is widespread use of venetian blinds to protect furniture.

How to cite this page:

Jock Phillips, 'Light - Scientific observation', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/light/page-2 (accessed 22 November 2019)

Story by Jock Phillips, published 12 Jun 2006