Applications

When Ultra Violet light is mentioned many people immediately think of either sunbeds, counterfeit money detectors, insect traps or fish pond disinfection units. However, ultra violet light is all around us, not just occurring naturally from sunlight but supplied by companies such as UV Light Technology Limited which, through high-tech industrial, commercial, public services and medical applications, make our daily lives more comfortable, secure, healthier and fun!

From treating vitamin D₃deficiencies and relieving the unsightly effects of Psoriasis, UV light is used in many treatments and research projects in the world of medicine. Latest medical breakthroughs include fluorescent dyes used in conjunction with blacklight to identify cancerous cells in the internal organs of patients.

In the worlds of science and engineering it is so often vital to establish the ageing effects of the sun on materials for safety and aesthetic reasons. Ultra violet light sources which closely correlate to natural sunlight are used in a vast range of applications from testing aircraft windscreens to examining the effects of degradation on building materials.

UV blacklight fluorescent inspection processes make working life easier for quality control engineers, forensic scientists, fire officers and auction houses to name but a few. Under UV blacklight hairline cracks can be detected in aircraft undercarriages, automotive steering systems and many other critical components upon which our lives may depend. In the field of forensics UV blacklight helps unearth vital evidence at crime scenes and plays an important role in identifying the cause of fires. The inspection of works of art under UV blacklight is a means of revealing imperfections and evidences of restoration, an important aspect of authentication for valuation and sale.

The special effects industry has embraced ultra violet blacklight for its ability to produce stunning visual effects as if by magic. Festival tented environments use UV responsive drapes, pop concerts use multi image 'trompe l'oeil' backdrops illuminated by UV and in night clubs UV is what makes your white clothes glow in the dark.

Microbiologists are employing UV-C germicidal lamps within engineering control measures to reduce infection caused by airborne transmission of bacterial pathogens within built environments. Furthermore, some of the water we drink has been disinfected using UV-C light, as has a wide variety of food, drink and medical supplies packaging.

In recent years UV light curing of materials has emerged as perhaps the most exciting and versatile material technology. These single component, solvent-free material systems cure almost instantaneously on exposure to UV light with efficient use of energy. They offer unrivalled and unique process advantages in times of stringent legislation changes restricting the use of many solvents. UV-A, UV-B and UV-C light sources are employed depending upon the type of material to be processed, ie: adhesives, resins, coatings or inks.

The high market growth rate of UV light curing is driven not only by processing and environmentally friendly benefits, but also its capability to provide innovative new processes and product developments. This cutting edge technology can often provide companies with the ability to exploit new business opportunities.

Definition

Ultra Violet (UV) light represents a section of the overall electromagnetic spectrum of light, extending from the blue end of the visible (400nm) to the x-ray region (100nm).

It is subdivided into three distinct wavelength regions described as either UV-A, UV-B or UV-C in increasing order of photon energy.

UV-A 400nm-315nm: Often referred to as 'blacklight', this is the longest wavelength region and lowest energy, it represents the largest portion of natural UV light.

UV-B 315nm-280nm: Partially blocked by the ozone layer this is the most aggressive component of natural UV light and largely responsible for sunburn (erythema).

UV-C 280nm-100nm: Only generally encountered from artificial light sources since it is totally absorbed by the earth's atmosphere.

Fluorescence and phosphorescence - Explained

The excitation energy provided by UVA photons is much higher than the energy of the thermal motions of the molecules at physiological temperatures. Thus the absorbing molecules temporarily assume energy levels that otherwise they would never attain and thus acquire properties differing considerably from those effective in ordinary chemistry.

The lifetime of a molecule in its usual excited state (10^-10 to 10^-8 sec), which is still long compared with the time required for the energy absorption itself (approximately 10^-15 sec), can be greatly extended if the excited electron is trapped in an (energetically somewhat lower) triplet excited state. In contrast to the usual singlet state, the triplet state is characterised by two electrons with unpaired spin. Because the return from the triplet state to the ground state is "forbidden" (i.e. occurs at a low probability), the triplet may last 10^-3 sec or even longer and is, therefore, called metastable.

As an excited electron returns to a lower energetic state, its excess energy can be emitted as a photon, resulting in fluorescence. Fluorescent light is recognised by its usually longer wavelength, compared with the exciting radiation. Emission from molecules in the metastable excited state occurs over a longer period of time and is called phosphorescence.

Application of fluorescence and phosphorescence for special effects

Fluorescent materials, whilst brighter than most materials under normal light, will glow only when illuminated with ultra violet (UVA) blacklight.

Phosphorescent materials will "charge up" under normal visible light and emit light in darkness. These may also be charged using ultra violet light, for brighter and often longer periods of light emission. As with fluorescent materials the phosphorescent equivalents will glow under exposure to ultra violet light, but phosphors continue to glow when the UV light source is removed.