Spectral and Spatial UV Sky Radiance Measurements at a Seaside Resort Under Clear Sky and Slightly Overcast Conditions.

Spatial measurements of the diffusely scattered sky radiance at a seaside resort under clear sky and slightly overcast conditions have been used to calculate the sky radiance distribution across the upper hemisphere. The measurements were done in the summer season when solar UV radiation is highest. The selected wavelengths were 307, 350 and 550 nm representing the UVB, UVA and VIS band. Absolute values of radiance differ considerably between the wavelengths. Normalizing the measured values by use of direct solar radiance made the spatial distributions of unequal sky radiance comparable. The results convey a spatial impression of the different distributions of the radiance at the three wavelengths. Relative scattered radiance intensity is one order of magnitude greater in UVB than in VIS, whereas in UVA lies roughly in between. Under slightly overcast conditions scattered radiance is increased at all three wavelengths by about one order of magnitude. These measurements taken at the seaside underline the importance of diffuse scattered radiance. The effect of shading parts of the sky can be estimated from the distribution of sky radiance. This knowledge might be useful for sun seekers and in the treatment of people staying at the seaside for therapeutic purposes.

Thermoreception and nociception of the skin: a classic paper of Bessou and Perl and analyses of thermal sensitivity during a student laboratory exercise.

About four decades ago, Perl and collaborators were the first ones who unambiguously identified specifically nociceptive neurons in the periphery. In their classic work, they recorded action potentials from single C-fibers of a cutaneous nerve in cats while applying carefully graded stimuli to the skin (Bessou P, Perl ER. Response of cutaneous sensory units with unmyelinated fibers to noxious stimuli. J Neurophysiol 32: 1025-1043, 1969). They discovered polymodal nociceptors, which responded to mechanical, thermal, and chemical stimuli in the noxious range, and differentiated them from low-threshold thermoreceptors. Their classic findings form the basis of the present method that undergraduate medical students experience during laboratory exercises of sensory physiology, namely, quantitative testing of the thermal detection and pain thresholds. This diagnostic method examines the function of thin afferent nerve fibers. We collected data from nearly 300 students that showed that 1) women are more sensitive to thermal detection and thermal pain at the thenar than men, 2) habituation shifts thermal pain thresholds during repetititve testing, 3) the cold pain threshold is rather variable and lower when tested after heat pain than in the reverse case (order effect), and 4) ratings of pain intensity on a visual analog scale are correlated with the threshold temperature for heat pain but not for cold pain. Median group results could be reproduced in a retest. Quantitative sensory testing of thermal thresholds is feasible and instructive in the setting of a laboratory exercise and is appreciated by the students as a relevant and interesting technique.

[Solar time--the importance of standard time for the UV-exposure of the skin]. / Sonnenzeit--die Bedeutung der gesetzlichen Zonenzeit für die UV-Exposition der Haut.

Dermatologists recommend that people avoid exposure to the blazing sun around noontime. In most places in Europe there are considerable deviations between true solar time and standard time: Firstly, during summer the standard time in the European countries is set one hour ahead according to the summer time or daylight saving time. Secondly, in all countries of Western and Central Europe, except Great Britain, Ireland and Portugal, standard time uniformly is Central European Summer Time (CEST). Although this standard central European time zone refers to the longitude 15 degrees East of Greenwich, it is valid for all longitudes up to nearly about 9 degrees West of Greenwich. This leads to a maximum deviation between standard time and solar time of nearly 1 hour and 36 min. Thirdly, a comparably small time shift is due to the equation of time. It amounts up to a maximum of about six and a half minutes at the end of July. Altogether, the shift between standard time and true solar time adds up to about 2 h 40 min at the Spanish coast of the Atlantic Ocean, e.g. noon is not at 12:00 but rather at 2:40 p. m. (14:40 h CEST).A paradoxical situation results for British holiday-makers who go to Spain. Although they move to a more westerly geographical position they do not put back their clocks but set them one hour ahead, since they enter the CEST zone. The recommendations given by dermatologists to the people regarding their exposure to the sun should allow for these geographical and astronomical facts.