New light Sources for Biomedical Applications

LED technology offers flexibility of spectral design and comfort in operation. This PhD thesis explores the potential health benefits that can be imposed by light interventions performed with ultraviolet (UV) light emitting diodes (LEDs) or visible (VIS) LED lighting systems. Based on a cross-disciplinary approach, combining competences from diverse scientific fields such as photonics, microbiology, photochemistry, chronobiology, and obstetrics the scope of this PhD project was 1) to investigate, by a systematic approach, effects imposed by narrowband UV irradiation, as emitted by LEDs, on systems with biological relevance and 2) to generate statistically significant evidence that VIS LED lighting systems, when used in a suitable manner, can improve several dimensions of human health and human performance.

A portable UV irradiation setup was fabricated and characterized. Bacterial communities forming biofilms and their inactivation by narrowband UV irradiation in the range 250-340 nm, was investigated. It was observed that regrowth was suppressed more effectively after UVB irradiation. Among the UVB LEDs tested, the diode at 296 nm showed the greatest potential for biofilm inactivation; radiant exposure at 20.000 J/m2 was proven adequate to totally inactivate immature biofilms.

This treatment was shown to be more effective than 1) photodynamic therapy, p=0.002 2) conventional antibiotics, p<<0.001; and 3) equally effective to combinatory antibiotics, p=0.12. However, effective inactivation (99.9%) on mature biofilms was only achieved after a novel treatment was invented, namely “light assisted antibiotics”.

Additionally, significant vitamin D enrichment of various food products was achieved. Especially the content of vitamin D in pig skin could reach 0.5 μg/cm2 after 7 sec. exposure versus the 0.005 μg/cm2 of not exposed samples, and 4 fold increase of vitamin D in egg yolk was demonstrated by direct illumination.

Applying VIS LED illuminants with specific spectral power distribution in elderly houses resulted in better sleep for elderly women (p=0.007). Light interventions enabled elite athletes to conserve their sleep quantity and quality, despite their shifted circadian rhythm. Easier vein identification-access was achieved by applying a special LED illuminant and a statistic evaluation of the human eye ability to identify veins was performed.

Finally, lower risks for C-section (OR= 0.57; 95% CI 0.33-0.97) were attained when labor rooms were equipped with dynamic illumination.