Umbrellas intercept the full direct flow that comes from the Sun, but not the diffused radiation that penetrates through from the sides.
"We have proven that irradiance (radiation incidence per unit of surface area) that reaches the ground covered by an umbrella is 34 percent of the total", José Antonio Martínez-Lozano, co-author of the study, highlights.
To carry out the Project the team positioned an ultraviolet ray sensor on the base of a canvas umbrella painted blue and white, with a radius of 80cm and height of 1.5 metres.
"The umbrella intercepts the direct radiation that comes from the Sun, but part of the diffused radiation, which makes up approximately 60 percent of the total, reaches the sensor from the sky not covered by the umbrella", explains Martínez-Lozano.
The results show that canvas has a very high capacity for absorbing radiation, "with only 5 percent transmissivity", but this does not prevent diffused ultraviolet radiation from penetrating through on the sides.
In addition, the team has developed a geometric model to obstruct the sky to calculate the irradiance that is received on the different horizontal and vertical planes under the umbrella. In the case of horizontal irradiance, the values that the model provides coincide with those registered experimentally with only a relative error of 3 percent.
In this way, and using various configurations of sky, ground and umbrella, the researchers have been able to simulate the real situation of people, who do not always remain lying down under sunshades, as they often tend to rise, sit or stand up.
Scientists believe that this study can help to gain a better understanding of the epidemiology of some skin cancers. An excess of ultraviolet radiation is not only related to the appearance of melanoma, it is also connected to sunburn, photoageing, many eye disorders – especially cataracts-, weakness of the immune system and DNA damage.
MEDICA.de; Source: FECYT - Spanish Foundation for Science and Technology