Your World in Ultraviolet

Ultraviolet light, more commonly called UV light or ‘Black’ light, is the higher energy sibling of Violet light. Human eyes are sensitive to wavelengths from 380 nm (Violet) to 750 nm (Red). Our retina can detect light up to the wavelength of about 310 nm (the entire UV A spectrum) but our lenses block this high energy radiation from reaching the retina, saving it from permanent damage. The UV light has a damaging effect on our skin and eyes, but fortunately, most of the UV rays from our sun (all of UV C and some of UV B radiation) are blocked by the ozone layer. Ultimately which reaches us is the higher wavelength UV A and some of medium wavelength UV B, both are responsible for causing skin damage. Although everything about UV is not horrific. An important beneficial aspect of UV is that our body uses UVB to produce a form of Vitamin D which is crucial for bone and muscle development.

Probably, the coolest thing about UV radiation is its capacity to cause fluorescence. Fluorescence is the absorption of a high energy photon by any molecule or particle, which then almost instantly re-emits it as a lower energy photon. What makes UV fluorescence particularly interesting is that if we expose UV light on objects (which is least visible), only the fluorescent objects emit visible bright light. But do not confuse this phenomenon with the glow-in-the-dark stuff! The latter is based on phosphorescence.

Fluorescence is used by scientists all over the planet to detect DNA, protein and lots of other chemicals. But does that mean, fluorescence is that one odd pearl, that sits on the shelves of science laboratories, used only for complex work? Not really. A lot of household materials exhibit fluorescence too, only if we have a UV light source to see them.

One such very common substance that fluoresces is Highlighter ink. The most commonly used yellow highlighters have a chemical compound called pyranine in their ink. Other coloured highlighters use Rhodamines. Such compounds are also used in hazard symbols in roads and danger areas as the UV emitted from the filament of headlamps of vehicles, makes the sign appear brighter in the dark. Our household detergents use fluorescent dyes, called Brighteners that fluoresce in the sunlight, making the whites appear whiter. Our teeth, nails, bones and even our urine, contain phosphors that make them glow under UV. Our skin has sebaceous glands that secrete sebum. But often, these glands are blocked by dead skin, dust and bacterial deposits, which ultimately cause acne. The bacteria, present in acne, secrete porphyrins which glow orange-pink in UV A light. This is the reason why your clogged pores and your dental plaque glow pinkish-orange under black light. Humans have stripes on their skin, called Blaschko's Lines, that become visible under a black or ultraviolet light, but they don't glow. Even Petroleum jelly or more commonly called Vaseline, glows too. Many gemstones such as rubies, few diamonds, and a lot of minerals including the common rock salt, exhibit fluorescence. Our kitchen packs its own set of surprises. The most common of it all is turmeric. Turmeric has a compound called Curcumin which is a fluorescent molecule in its dissolved state and glows bright yellow. Honey, olive oil, canola oil, ketchup, and banana spots glow too. Perhaps the most striking example is tonic water. It contains Quinine which glows blue under UV, distinguishing a bottle of tonic water from a normal one. Moving towards the garden, the most abundant pigment Chlorophyll glows red under UV. Some insects and arthropods, such as scorpions, have a hyaline layer, which is a very thin but super tough coating in their exoskeleton. This hyaline layer makes them glow when exposed to UV light. Some flowers, like four-o'clock, contain pigments called betaxanthins, which show flashy glow under black light.

Beneath what we normally see, lies an enormous ocean of what we don’t observe. Shining UV light on various things gives us a glimpse of that unknown. Taking necessary precautions, exploring your house or garden using a UV torch might be a fun activity that will quench your curiosity for sure. Who knows what lies waiting, to be discovered.

- Agradeep Mukherjee

4^th Year
Department of Biotechnology,

References:

https://www.newscientist.com/lastword/mg24432591-000-super-seers-why-some-people-can-see-ultraviolet-light/

https://www.who.int/uv/faq/whatisuv/en/index2.html

https://www.fda.gov/radiation-emitting-products/tanning/ultraviolet-uv-radiation

https://www.horiba.com/en_en/technology/measurement-and-control-techniques/spectroscopy/what-is-fluorescence-spectroscopy/

https://www.compoundchem.com/2015/01/22/highlighters/

https://www.thoughtco.com/what-glows-under-a-black-light-607615

https://www.hauntforum.com/archive/index.php/t-11422.html

https://sciencenotes.org/list-of-things-that-glow-under-black-light/

https://www.ncbi.nlm.nih.gov/pubmed/21091785