Regarding UV Flashlights

[jjrakman]

I initially wanted to experiment with UV flashlights for two reasons.

1. The idea that if any kind of UV sensitive material is created as a result of a ghost manifesting the UV light might amplify is visibility to the eye or the camera.

2. As Noah points out, there is no contamination of evidence in regards to Nightshot videotape. The UV light does not show up on infrared video.

However my concern has always been the preservation of night vision.

I've been doing some research and here's what I've found.

I think everyone knows that prolonged exposure to UV light can cause lesions and inflammation of the cornea. But I don't think that the levels that the flashlights are putting out can cause that. If you can stand sitting in a nightclub lit with blacklights for an extended period of time, then these flashlights should pose no problem in that regard.

One of the reasons that Ghost Hunters began using flashlights with red gels, was to preserve an investigator's night vision. Cockpits in aircraft are now lit entirely with red light for this very reason. To preserve a pilot's night vision.

Inside of your eye you have various cells that act as receptors for light. Rods and cones.

The cones detect Red Blue and yellow light.

But what really concern us here is the rods. The rods help in detecting peripheral vision and motion. But their primary function is to aid in the seeing in low light level situation, or to give us night vision.

The way this works is that the rods are coated with a chemical pigment called rhodopsin or visual purple. This chemical is what aids in a person's night vision. When it is exposed to bright light, the rods are bleached and then must once again reproduce the rhodopsin in order to regain night vision.

Unfortunately, rhodopsin also breaks down faster when exposed to shorter wavelengths of light, such as UV, but can be maintained in longer wavelengths such as red. In addition, UV tends to make radicals out of everything, which further contributes to the breaking down of rhodopsin.

So essentially it's a horse apiece.

Use red flashlights and maintain your night vision, but contaminate the video evidence.

Use UV flashlights and lose your night vision, but do not contaminate the video evidence.

I suppose we could experiment with placing a red gel over the UV flashlights to see if we could get the best of both worlds.

[Arkman1982]

Interesting. I was under the impression that UV would not effect night vision. We could try a red gel on the UV light. I have never had problems with the UV light that I used as far as losing night vision. It may have been because I thought it wouldn't affect night vision so I didn't take special notice of the effects before and after turning it on. That may be because I usually am looking at my LCD screen of my video camera which would kill my night vision anyway. I definitely think that evidence is more important than night vision but that may be just me. We need to get some red gels I guess. I still think everyone should get UV flashlights.

[jjrakman]

Well I'd say the jury is still out on UV flashlights and more experimentation needs to be done. I think both UV flashlights and red gels may have usage in different applications. For instance, if any nightshot video isn't being shot, I think using red gels would be preferable.

Here's some other considerations that were brought up on the IPI board.

UV flashlights could also be used during an initial visit to help bring out any potential hoaxing apparatus.

UV light can strike an object and reflect light in a different wavelength, kind of when you look at a blacklight poster that's all glowy, in that case the returning light does invade the range of nightshot. But conventional light does that anyway.

In addition, if a manifesting entity can somehow be enhanced by UV illumation in the same way a black light poster can, then UV flashlights could be a real benefit.

In the end more experimentation needs to be done. I think we should still give the all UV a shot. I've never seen it done before.

[jjrakman]

Additionally in regards to the night vision vs. evidence contamination argument, I'd say a paerson would have to determine in which situation which is better. Either one may not be desirable in all situations, we just don't know yet.

It's kind of like the motorcycle helmet argument. Do helmets save lives? If you get into an accident maybe. But does the loss of peripheral vision and muffled hearing increase the chances of getting into an accident in the first place?

In other words, UV may not contaminate evidence, but if it dulls your nightvision will you be able to spot out a potential manifestation to aim the camera at?

Who knows.

Additionally I think maybe the infrared saftey glasses seen on CSI may aid in maintaining nightvision when using UV flashlights, I'll have to research that.

[Arkman1982]

After our illegal ghost hunt the other night in which we realized that UV light was visible on the night shot cameras, although only under certain conditions, it has been bothering me. I did a little search online and came up with this possible explanation:

Switching to 'Nightshot mode' physically displaces the camcorder's internal glass filter called "IR Cut Filter (ICF)", which means that much more NIR light reaches the CCD. In-between the optical lens and the CCD, most camcorders have this special "ICF". It is there to compensate the colorings and the tones of the information reaching the CCD by blocking the NIR and ultraviolet rays. Since the CCD is originally more sensitive to NIR rather than the visible rays, as shown at the graph below, it would be impossible to create a natural image on the viewfinder or LCD screen for the human eye without this ICF. However, this ICF, which blocks off the NIR, is the biggest obstacle in seeing-through and night viewing.

It seems turning it on NightShot removes the innate UV and IR filters. That being said, I have a UV filter that is made to block out UV waves from the sun. I am not certain, but maybe if I add this to my camera, it will filter out the UV and I will obtain the desired effect. I plan on testing this soon at my house and at the investigation next weekend. If anyone else has the time and equipment it would be cool if we could test this with more than one camera and flashlight.

[steveg]

Here's a little more on this topic...

I tried one of the so-called "X-Ray Filters" with nightshot and a UV flashlight and here are the results.

Without the X-Ray Filter, the UV flashlight showed up when using nightshot.

With the X-Ray Filter, the UV flashlight DID NOT show up when using nightshot.

The X-Ray Filter only lets IR light through. Lower frequency light (UV) is blocked. The filter I tried was a 950nm filter. It is meant for use in bright sunlight (although I have never gotten around to trying it). The brightness was really cut back when using this filter. I know that you can get lower frequency filters. I am guessing that they will not affect the brightness as much as the one I tried.

[Arkman1982]

Interesting. I have yet to try my UV filter. I know that it doesn't affect brightness very much. I hope to try it out sometime this week. I don't think I have an X-ray filter although I believe I have heard of them.

[steveg]

Do an eBay search on "IR Filter 37mm". Again, the filter I tried was a 950nm filter. It did get rid of the UV light completely, but it also got rid of a lot of the IR light, making the picture darker. Since IR illuminators actually emit near-ir, a 760nm filter would probably work a lot better than the 950nm. It should let a lot more of the near-ir light through while blocking the UV light.

[steveg]

OK, I got a 720nm filter and tried it. The picture was very slightly darker with the filter than without. This test was with nightshot mode only, no external illuminator. Without the filter, my UV flashlight showed up clear as day. With the filter, you could not see it at all. It looks like this is a solution to the UV flashlight problem.

[Arkman1982]

AWESOME!!! A trailblazing we will go. Great work Steve. I will be getting one for myself here in a little bit. Thanks for reporting on it!