The UV-index is an international standard measurement of the strength of erythemogenic ultraviolet radiation. It is often published in the media and then refers to the highest expected UV radiation for that day. The highest UV-index value measured in Iceland is seven. Although this is similar to the maximum values from southern Scandinavia, the average UV-index is lower in Iceland compared to other Nordic countries. Around solar noon the UV index is roughly equivalent to the Standard Erythema Dose (SED). During a bright summer day in Iceland the number of Standard Erythema doses can go as high as 32, but is on average in June around twenty. The typical Icelander gets red after 4-6 SED and it is obvious that during solar noon it is easy to sunburn in Iceland if you stay outside without sun protection.

Sigurgeirsson B, Wulf HC
Key words: UV index, ultraviolet radiation, standard erythema dose, sunburn.
Correspondence: Bárður Sigurgeirsson, bsig@hudlaeknastodin.is

Figure 1. The electromagnetic spectrum reaches from low energy radio waves with long wavelengths to high energy gamma rays with short wavelengths. The ultraviolet spectrum is found between the blue part of visible light  and the x-rays.

Figure 2. The erythema action of ultraviolet radiation on the human skin (red line). The blue line shows the absorptions spectrum of DNA.

Effect on skin	Skin reaction	Comments
Immediate	Sunburn	Mainly caused by UVB rays
	Immediate pigmentation	Melanin precursors are oxidized to melanin. Only takes minutes a few hours.
	Late pigmentation	Starts 24-72 hours after UV exposure. Mainly caused by UVB induced DNA damage
	“Lichtschwiele”	UVB induced thickening of stratum corneum which can increase UV absorbtion. Only UVB exposure has this effect
	Immunosuppression	Both local and systemic
Late	Photoageing	Solar elastosis, telangiectasia, pigment changes
	Skin malignancy	Basal cell carcinoma, Actinic keratosis, Malignant melanoma

Table I. The effect of UV radiation on the skin

 

 

Over 90% of UV radiation can penetrate light cloud cover

Snow reflects up to 80% of erythemogenic UV radiation

60% of ultraviolet radiation in Iceland is received between 11:30 and 15:30.

UV-index increases by 4% for each 300 meter increase in altitude

Staying in the shade reduce ultraviolet radiation by 50%

White sand at the beach reflects up to 15% of UV radiation

Table II. A few facts regarding UV-index and ultraviolet radiation