ISO 12312-2:2015—Solar Eclipse Glasses

A solar eclipse is a spectacular, awe-inspiring astronomical event that drastically changes the appearance of the two biggest objects we see in our sky: our Sun and Moon. On Earth, people can experience solar and lunar eclipses when Earth, the Moon, and the Sun line up. Safety is the number one priority when viewing a solar eclipse. ISO 12312-2:2015— Eye And Face Protection – Sunglasses And Related Eyewear – Part 2: Filters For Direct Observation Of The Sun provides specifications for proper observing methods of the sun, such as when viewing the solar eclipse.

Why Is Viewing the Sun During A Solar Eclipse Dangerous?

Exposing your eyes to the sun without proper eye protection during a solar eclipse can cause retinal burns (solar retinopathy). Exposure of the retina to intense visible light causes damage to its light-sensitive rod and cone cells. The light triggers a series of complex chemical reactions within the cells which damages their ability to respond to a visual stimulus and, in extreme cases, can destroy them. The result is a loss of visual function which can either be temporary or permanent, depending on the severity of the damage.

ISO 12312-2:2015 highlights that it is never safe to look at a partial or annular eclipse, or the partial phases of a total solar eclipse without the proper equipment and techniques. Even when 99 % of the sun’s surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent sun is still intense enough to cause a retinal burn even though illumination levels are comparable to twilight.

What Is ISO 12312-2?

ISO 12312-2:2015 applies to all afocal (plano power) products intended for direct observation of the sun, such as solar eclipse viewing. It specifies that welding filters are designed to protect the eyes against ultraviolet, visible, and infrared light; whereas, the filters for direct observation of the sun need only to provide protection against visible light.

Why Do Solar Eclipses Not Occur Every New Moon?

A new Moon is essentially the opposite of a full Moon. During a new Moon, we see the side of the Moon that is not being illuminated by the Sun, making it appear that the Moon is blending in with the night sky.Although a new moon happens about once a month, solar eclipses do not. This is because the Moon does not orbit in the same plane that the Sun and Earth are in (the ecliptic plane).

The Moon’s orbit is tilted (or inlined) 5° compared to Earth’s orbit around the Sun. During the new moon, the Moon usually passes below or above the Sun, and its shadow misses Earth. There are only two times a year, called “eclipse seasons,” when the new moon crosses the Earth-Sun (ecliptic) plane and provides opportunities for solar eclipses: the Sun, the Moon, and Earth are aligned, or in syzygy.

Solar Eclipse Safety

ISO 12312-2:2015 details that eye protectors for direct observation of the sun should be worn so that no direct radiation from the sun can reach the eye other than that passing through the filter. Further, during eclipses of the sun, eye protectors should be worn whenever a part of the disk of the sun is not covered by the moon (i.e. during partial eclipse). The only time it is safe to view the sun without an eye protector is when the moon completely covers the sun in total eclipse

ISO 12312-2:2015— Eye And Face Protection – Sunglasses And Related Eyewear – Part 2: Filters For Direct Observation Of The Sun is available on the ANSI Webstore.