Skip to main content
Hong Kong Observatory Brand Hong Kong - Asia's world city
GovHK Traditional Chinese Simplified Chinese Search Search Site Map Contact Us
red dot
Print Version
Print Version PDF Version


Erythemal action spectrum : The response of skin to ultraviolet radiation of different wavelengths. (Click here to look at the spectrum curve)

Infrared Radiation : The wavelengths of infrared radiation are longer than those of visible light and range between 700 and 1,000,000 nanometers (nm) [1nm = 10-9m].

Intensity : The amount of radiation energy fell on unit area per unit time.

Ozone layer :  The layer of the atmosphere in which the concentration of ozone is greatest. Typically, the ozone layer lies between altitudes of 20 to 25 kilometre.

Photochemical smog :  Smog produced by action of solar radiation, especially of ultraviolet radiation, on exhausts from vehicles and industry.  Photochemical smog irritates the eyes, nose and throat and damages plants. As smog increases, it can trigger more serious health problems e.g. asthma, bronchitis, increased susceptibility to respiratory infections and decreased lung function.

Radiation : The transmission of energy by electromagnetic waves or particles.

Spectrophotometer : An instrument for measuring the intensity of radiation as a function of wavelength.

Sun Protection Factor (SPF) :
The Sun Protection Factor gives an indication of the effectiveness of the sunscreen lotions on protecting the skin from sunburn.  The higher the SPF, the greater the protection. For example, a sunscreen lotion with SPF 4 means that the exposure to ultraviolet (UV) radiation received after a given time is one-quarter that received in the absence of any protection.



Last revision date: <19 Dec 2012>