Ultraviolet irradiance: an insight into the principles of UV rays and its impact on micro-organisms

Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light. UV rays are classified into three different bands based on their wavelength:

1) UVA rays

  • the longest wavelength of the three: 320-400 nm.
  • the capability of reaching deep into the body causing DNA to react
  • prolonged exposure can cause skin cancer to human beings

2) UVB rays

  • wavelength between 290-320 nm.
  • do not penetrate deep into the skin, has an impact only on the epidermal skin
  • often termed as ‘tanning rays’

3) UVC rays

  • the shortest wavelength ranging between 100-290 nm.
  • normally do not reach the Earth’s atmosphere
  • prolonged exposure can be fatal
  • the basis of our discussion today

 

UVC rays can be fatally harmful to living beings. If emitted at a wave length of around 254 nm, it has the capacity to react on one of the nucloebases of DNA, thymine, by breaking its bond with adenine and thereby completely disrupting cell replication. Exposure to UVC rays causes the micro-organisms to be effectively harmless as it reduces their ability to reproduce, thus leading to their ultimate extermination. For this reason, light of short range wavelength is also called germicidal UV. It is mutagenic to micro-organisms like fungi, bacteria and molds.

Benefits for the Leather and Shoe Industries:

  • can effectively prevent mold formation
  • even if mold is identified, can stop further damage immediately
  • reduces or eliminates rework costs due to mold
  • installation / maintenance / operation costs of UVC lighting is very low

 

How is it done?

The process of killing micro-organisms is called Ultraviolet Germicidal Irradiation (UVGI). It is done by installing germicidal UV bulbs in special chambers. The object to be treated is exposed to the light produced by the UVGI bulbs under controlled conditions (i.e. between 30 and 60 seconds).

UVGI germicidal bulbs

Germicidal UV can be delivered by a mercury vapor lamp that emits UV at 254 nm. wavelength. Special transformers are used to ensure even electric flow to the bulbs. They still produce some visible light due to emissions of the mercury radiation bandwidth. Some common UVGI bulbs are:

  • low pressure lamps similar to fluorescent lamps with a wave length of 253.7 nm.. The tube is made of fused quartz which allows the light produced by the mercury arc inside to pass out of the lamp unmodified
  • medium pressure lamps quite similar to HID (High Intensity Discharge) lamps. They radiate a broad-band UV radiation in a single line. Mainly used in the water treatment industry due to its very intense radiation. It produces a bright bluish light.

 

Safety concerns:

  • UVC is harmful to humans
  • can cause sunburn and is carcinogenic
  • can cause inflammation of the cornea
  • can also damage the retina
  • can lead to permanent vision impairment

 

Industrial precautions:

  • any shade on the product to be treated can reduce the impact of the UVGI light; therefore the material to be treated must be in direct ‘line of sight’ of the radiating bulbs
  • dust on either the material or the bulbs can reduce the impact of the treatment; therefore the material must be dust free and the UVGI bulbs must be periodically cleaned
  • light produced by UVCI germicidal lamps must be carefully shielded to prevent direct viewing, reflextions and / or dispersed light from affecting factory operators.
  • prolonged exposure (15-30 minutes) can fade the color or materials.

 

                                     Contributed by Sandeep Yadav (Impactiva’s India Team)