New research reveals that beach umbrellas may not provide the level of sun protection that, to date, many had assumed they would. According to researchers from the University of Valencia in Spain, while beach umbrellas block most of the ultraviolet (UV) radiation coming directly from the sun, a percentage of the scattered or reflected UV radiation still reaches beneath the shelter.
Prolonged exposure to UV radiation has been shown to have a variety of detrimental health effects on humans, including; sunburn, immune system suppression, ocular damage (cataracts), premature skin aging and the development of skin cancers. The solar UV radiation directly from the sun and its encircling light only makes up approximately 40% of the total radiation which may reach a person’s skin at ground level. The other 60% comes from the surrounding sky, it may be reflected from the surface of nearby objects, such as buildings, trees and sand, or it may be scattered by the molecules which make up the air. This reflected UV radiation is known as ‘diffuse radiation’ and is able to penetrate horizontally through unobstructed sections of the sky.
The experiments, undertaken by the Solar Radiation Group at the university, involved the placement of a light sensor near the centre at the base of a beach umbrella. The umbrella, width 160 cm and height 100 cm, was made of a canvas material painted blue and white. The tests were performed under cloudless skies during the hottest part of the day and involved the use of a ‘shadowband’; an instrument which blocks out direct sunlight in order to measure the UV radiation from other sources.
The study revealed that the beach umbrella absorbed the majority of direct solar radiation, approximately 95%. However, a considerable amount (on average one third) of the diffuse radiation from the sky surrounding the umbrella was not intercepted and was able to reach the sensor beneath it. In order to mimic a person in an upright position beneath the umbrella, a vertical sensor was also used. In this case, the diffuse irradiance transmitted was lower, only 17%, and even less some distance from the centre of the umbrella.
Due to the complex nature of the environment it is expected that these results could vary, dependent on: the size, colour and material used in the umbrella; the size of the person beneath it; the reflectance of the surface the umbrella is positioned on; and environmental conditions such as the latitude, season, amount of pollution and cloud cover. It is thought that surrounding obstructions, such as neighbouring umbrellas or other people on a crowded beach would also alter the level of diffuse irradiance. In addition, as live subjects were not used, the study was unable to determine the extent of skin damage likely to be incurred under such conditions.
Prior to this investigation, the danger of diffuse UV radiation was a threat that most had not considered. Upon discovery that UV radiation is able to infiltrate a shelter via the sides exposed to the sky, it becomes clear that a beach umbrella alone cannot offer 100% defense against the sun’s rays. Thus, it is advised that umbrellas, and other partial shades, be used in conjunction with additional protective measures such as hats, clothing, sunglasses and sunscreen. These results may be particularly significant for the parents of infants and young children who have previously relied on such shelters to protect their family.
Reference
Utrillas, M.P, Martínez-Lozano, J.A & Nuñez, M, 2010, ‘Ultraviolet Radiation Protection by a Beach Umbrella’, Photochemistry and Photobiology, 86:449-456.
Image reference
‘Beach Umbrella’ uploaded to flickr.com by ‘monkeyatlarge’ on the 5 August 2005, <http://www.flickr.com/photos/monkeyatlarge/31522767/>.
