Comparison of performance and safety of four different UV light tubes

Time and time again we’ve seen organisations run in to trouble from fitting the wrong tubes in to their UV light equipment. This is often a result of purchasing looking to source cheaper alternative tubes or a lack of knowledge when it comes to UV light.

For example, we’ve seen huge mistakes been made with companies using the incorrect UV-A tubes for inspection (either the wrong wavelength or insufficient irradiance levels), leading to parts passing quality control when the correct lighting would have picked up the defects.

We’ve also seen organisations replace UV-A tubes with more harmful UV-C sources, causing adverse health effects to innocent members of staff.

It’s another reason why information and training is so important within organisations using artificial UV light sources. There is also a lot of misinformation out there from companies that supply and re-sell UV lamps who are not specialists in the industry.

Consequences include:

  • Process complications (not meeting the minimum levels required for the process)
  • Safety issues (causing health and safety issues from over exposure to UV light)

To help demonstrate this we took readings of four different tubes, all of which were the same length, fitting and similar wattage – and made both UV irradiance and UV safety readings all at the same position.

Applications and uses

Fluorescent inspection

Many critical quality control procedures rely on UV fluorescent processes, such as oil and fluid leak detection in the automotive industry and crack detection in aerospace applications.

Generally there is a minimum UV irradiance level required to achieve the best results – however installation of the wrong replacement tubes can lead to insufficient levels, compromising the whole process. We’ve seen this lead to hugely expensive product re-calls and re-work, costing organisations a lot more than the difference between the right and wrong replacement UV tube.

As you will see in the table below, you can purchase what on the face of it looks like identical blacklight blue UV tubes (same length, wattage, fitting and peak output) but the actual measured UV light output can be much lower. It’s why organisations should always contact the supplier of the original equipment to discuss replacement lamps.

Insect control

Blacklight (BL) lamps are used as a way of enticing insects such as wasps and flies in to traps as a means of controlling insects and pests, particularly in food and healthcare settings.

One of the worst cases of over exposure in the workplace we have come across was when a maintenance engineer replaced blacklight tubes with germicidal tubes (not knowing there was a difference), which resulted in kitchen staff being significantly over exposed.

Disinfection

Shortwave UV-C light will break down the DNA and RNA or micro-organisms, rendering them useless and unable to replicate. However, these lower wavelengths are much more dangerous to the skin and eyes, meaning you can exceed the exposure limit values in a matter of seconds, rather than minutes or hours.

Maximum permissible exposure times

The Control of Artificial Optical Radiation at Work Regulations 2010 define the maximum permissible exposure times for the skin and eyes within an 8-hour period.

We measured and calculated the maximum exposure times for all 4 units, with the measurements taken at the same position and distance (15″) from the source.

As you can see, the exposure times varied from 3 hours and 40 minutes for the skin and 30 minutes for the eyes (type 2) to just 3 seconds for the skin and eyes (type 4).

This drastically demonstrates the importance of having the right information and training when it comes to UV light sources in the workplace.

A comparison of four different UV light tubes

Type 1
Type 2
Type 3
Type 4
Manufacturer
Narva
Eiko
Sylvania
Philips
Length
24″
24″
24″
24″
Wattage
18W
18W
20W
17W
Fitting
T8
T8
T8
T8
Peak output
365nm
365nm
350nm
254nm
UV range
UV-A
UV-A
UV-A
UV-C
Type
Blacklight blue
Blacklight blue
Blacklight
Germicidal
Primary purpose
Inspection
Inspection
Insect control
Disinfection
365nm reading @ 15″
1,080 uW/cm2
380 uW/cm2
860 uW/cm2
32 uW/cm2
254nm reading @ 15″
0 W/m2
0 W/m2
0 W/m2
19.75 W/m2
MPE @ 15″ (Skin)
02:20:00
03:40:00
00:40:00
00:00:03
MPE @ 15″ (Eyes)
00:15:00
00:30:00
00:12:00
00:00:03

UV light spectral output for the UV tubes

As shown in the spectral graph below, type 4 emits a lot more of it’s energy at 254nm, well within the UV-C region which has much greater potential to cause adverse health effects. Whilst the other three types are all within the UV-A region, there are still exposure limits that need to be adhered to.