ultra violet light

[Guest david]

hi all! I am going to shoot a music video in london and would like to use uv-light to make all white glow. it will be shot in a studio and we will prepare with mostly black and white elements.

I have never done anything like this and would like to know if there is anyone who has experience of this topic.

some questions like how will I messure the ultra violet light and what kind of light can I mix the ultra violet light with? is that possible?

should I shoot it on 16 or 35 mm?

would be very happy for some advice.

/david

[Phil Rhodes]

Hi,

 

I did a fairly complex UV shoot a while ago, involving multiple layers of separation on a costume. It was video, but I found that it was actually quite easy to have the UV reactive colours start to bleach - it doesn't look like much, since it's diffuse, but the surface luminance can get quite high.

 

For film, I guess you'll have to spot meter a glowing object and make an educated guess. What kind of effects are you after, and what kind of UV sources do you have?

 

Phil

[Mitch Gross]

You'll find that the regular fluorescent UV light fixtures (aka "blacklights') will not have much strength or directional control. There are a couple of companies that make pro-style lighting fixtures with UV bulbs. Wildfire is a leader in this, and they also make fluorescent paint that will work well with these fixtures.

 

You'll generally need to keep the ambient light level down in order to work well with the UV glow. Best way (other than by eye) to meter is with a spot meter. Check out "Batman & Robin" and "The Game" for some nice UV lit scenes.

[Guest david]

thanks for fast replies! I have not yet found what kind of light sources I will use. I´ll check out wildfire. I´ll guess I dont need so powerfull sources. all I like from them is a classic uv glow on all whites, clothes, white make up etc.

should I use tungsten light and use it as back light to keep as much as possible of the uv?

when you wrote about fluorescent paint. does that mean I don´t need uv light or do I use it together with uv-ligth?

the level in their faces and the rest of the set can be low key but I will still need to get recognition of them and the set.

/david hellman, stockholm

[Guest Chainsaw]

What Mitch said.

Standard fluorescent tube UV and incandescent UV sources have incredibly weak output. It would take multiple upon multiple units to even begin to accomplish anything close to an adequate level for exposure. Additionally these consumer fixtures do not have standardized UV wavelengths. Some even spike light into the visible spectrum which only serves to diminish the fluorescent effect of a UV source. The filament based bulbs will also devitrify quite fast during use due to their high operating temperatures and treated glass. This causes an overall decrease in light output and a general warming of color temperature that will pull your light further from the UV wavelengths. The fluorescent tube based UV bulbs do not do this but they are an omnidirectional soft source with weak throw and little control. Almost useless when used outside of a black velvet Bob Marley poster.

 

If you need a high-yield, controllable UV source I definitely recommend renting a few WILDFIRE units. Wildfire manufactures many high-output fresnel UV lamps specifically designed for the motion picture and theatre industry. These are arc lamps that function very similarly to HMI units, with ballasts, head cables and all. Wildfire also manufactures many paints, dyes, fabrics, powders, and backdrops designed with fluorescent properties when struck with UV radiation. These items look perfectly normal until lit with UV. Basically fluorescence is the luminescent property of a material that when struck with one wavelength of radiation it emits radiation (photons) of another wavelength. In this instance normally invisible UV light is reradiated as light in the visible spectrum, i.e., it causes an object to glow. Any given fluorescent material must be lit with UV for a visible effect to occur.

 

Every object fluoresces differently (if at all) and each individual object needs to be treated as a separate source of light. The only practical way to measure them is with a spot or reflective meter. Always remember that your meter will try to average out these "sources" at 18% or neutral reflectance, so consider how bright and saturated you want these objects to be based upon that. Whatever medium you shoot I earnestly recommend using a UV filter. This will not eliminate the effects of your UV sources but it will prevent any stray UV from fogging your image. UV light focuses at a different distance than visible light so under most shooting circumstances it will soften your image. In addition to this, film is highly UV sensitive and in a studio environment stray UV could seriously over-expose your image.

 

While Wildfire sources are perfectly safe, they operate at approximately 350nm (UV-C wavelength); it can be difficult to properly judge a scene by eye when using them. Not only will your eye focus the UV light at the incorrect distance but the vitreous humor in the eye (the fluid that determines the shape and structure of the eye) will fluoresce at 350nm. Your eyes will actually glow from the inside out. This is more a nuisance than a health risk but it may be visually disturbing if you need a close-up of an actors face.

 

For an educated decision on film stocks you will need to do lighting and wardrobe tests first. I DP'd a short film some time ago where we had an entire black wall decorated with symbols in Wildfire paint. I had ordered 5274 for this scene but when I arrived on set I realized that the Production Designer had used a Violet Wildfire paint that had very little fluorescence compared to the rest of their line of paints. This coupled with the size of the wall necessitated a rush order of 5289 so we could shoot with an acceptable stop. While not as saturated as I would have liked, the 800T did quite well.

 

During said scene we did mix UV and other "white" sources, however they were very carefully controlled and not allowed to mix whatsoever. If you plan on lighting an object with UV I recommend using only UV on said object. Any other light source will only overpower your UV and destroy whatever effect you are trying to achieve. Tungsten sources are incredibly weak in the UV end of the spectrum and HMI's have UV treated safety glass. Neither can be properly converted to UV, although Congo Blue gel can come fairly close. The drawback to that gel is that it cuts your light transmission to .3%. If you do introduce white light do so with extreme discretion and control.

 

If you would like some examples of fairly straightforward UV photography here are two links to consider:

 

I'm the one who steps from the shadows,

 

all trench coat and cigarette and arrogance, ready to deal with the madness.

 

Both were shot on Kodak 160T reversal with a single 400w Wildfire unit (and a bounce card) and processed normal. The "model" was lathered in liquid Tide detergent so that his skin would fluoresce under the UV source. My choice of reversal was for the high contrast and deep color saturation and I used the tungsten balanced stock for a deeper punch toward the blue end. These examples are highly compressed and lack the fine detail of the original transparencies, but you get the idea...

 

 

I apologize for the inconvenience but due to the inherent idiocy of my host site the above links are no longer working. Same as it ever was...

Edited February 8, 2004 by Chainsaw