Light intensity at a distance -- UV light to kill bacteria

In summary: But to give you a general idea, 254nm UV is the most effective wavelength to inactivate spores of many common pathogens.
  • #1
ahk
1
1
TL;DR Summary
If I've got a bulb producing about 5J/s of useful energy at 253.7nm then how much useful energy do I have at .254m (10")?
I have obtained seeds of a rare rhododendron species.

These seeds are contaminated (experimentally determined). While I have tried several common methods, none decontaminated the seeds.

Lately, I have read that so many joules of UV light at approximately 254nm will prevent replication and inactivate or kill bacteria, fungus, mold... even in the spore stage.

I don't need a perfect number as it seems that too much UV (within reason) won't damage seeds.

My light bulb is 25W. I have read that an average Ag bulb of this wattage produces about 5W at 254nm. Using 5W at 254nm and .254m as my distance, when I try to use (what I think is) the appropriate equation (Intensity=W/m^2), I get a ridiculous answer of 77.5W/m^2.

Can anybody help?

Thanks.
 
Biology news on Phys.org
  • #2
ahk said:
Summary: If I've got a bulb producing about 5J/s of useful energy at 253.7nm then how much useful energy do I have at .254m (10")?

My light bulb is 25W. I have read that an average Ag bulb of this wattage produces about 5W at 254nm. Using 5W at 254nm and .254m as my distance, when I try to use (what I think is) the appropriate equation (Intensity=W/m^2), I get a ridiculous answer of 77.5W/m^2.

Your source is generating 5w of power which represents the flow of energy. At .254 m this flow is spread out over the surface area of 4π(.254)2 m2 = 0.811 m2 so the flow of energy can be expressed in terms of watts/cm2. So 5W/0.811 m2 = 6.17 W/m2 = 6.17x10-4W/cm2

ahk said:
Lately, I have read that so many joules of UV light at approximately 254nm will prevent replication and inactivate or kill bacteria, fungus, mold... even in the spore stage.

I believe UV dose is usually expressed in watts⋅sec/cm2.
 
  • Like
Likes jim mcnamara and ahk
  • #3
UV dose to kill (or inactivate) different species various among the different species, sometimes by a large amount.
Here is a pdf (from a different thread) that has a information on a lot of different organisms UV sensitivity. There are many other similar lists around.
 
  • Like
Likes jim mcnamara and ahk

1. How does light intensity affect the ability of UV light to kill bacteria?

The intensity of UV light is directly related to its ability to kill bacteria. Higher intensities of UV light have a greater impact on bacterial cells, leading to a higher rate of destruction. This is because higher intensities of UV light contain more energy, which can damage the DNA and other vital components of bacterial cells.

2. What is the optimal distance for UV light to effectively kill bacteria?

The optimal distance for UV light to kill bacteria depends on various factors such as the type of bacteria, the intensity of the light, and the duration of exposure. Generally, a distance of 6-8 inches is recommended for most UV light devices to effectively kill bacteria.

3. Can UV light kill all types of bacteria?

UV light is effective in killing a wide range of bacteria, including both gram-positive and gram-negative bacteria. However, some bacterial species may be more resistant to UV light and may require higher intensities or longer exposure times to be effectively killed.

4. How long does it take for UV light to kill bacteria?

The time it takes for UV light to kill bacteria depends on the intensity of the light, the distance from the light source, and the type of bacteria. Generally, it can take anywhere from a few seconds to a few minutes for UV light to kill bacteria.

5. Is UV light safe for humans?

UV light can be harmful to humans if proper precautions are not taken. Prolonged exposure to UV light can cause skin damage, including sunburn and an increased risk of skin cancer. It is important to use UV light devices carefully and according to the manufacturer's instructions to minimize any potential risks.

Similar threads

Replies
7
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
1
Views
871
  • Electrical Engineering
Replies
5
Views
2K
Replies
4
Views
951
  • Biology and Medical
Replies
5
Views
5K
  • Introductory Physics Homework Help
Replies
1
Views
1K
  • Electrical Engineering
Replies
1
Views
3K
Replies
1
Views
1K
Back
Top