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- - - Light Contamination
Dental Radiography QA
Processing Errors
Light Contamination
As well as generalised fogging caused by exposure of the whole film to light, there are other ways that light can affect a film when an automatic processor is used.
What processing error has caused this pattern of light and dark?
Automatic developers have a "dark box" with hand holes in the side. The film is unwrapped in the dark box.
If light can enter the box through the wrist-holes, this pattern commonly emerges. Dark areas appear where light reaches the film. Normal areas are where the fingers and thumbs were holding the film during unwrapping, protecting it from the light.
Under what circumstances is this likely?
When the person has thin wrists that do not completely fill the hand-holes. If this happens, the holes should be modified or replaced with smaller ones.
What processing error has caused this pattern of light and dark?
The problem here is that the hands were removed from the box too early. The film had not totally left the dark box and entered the developing compartment - there was still a little bit poking out of the rollers.
When the hands were removed, light entered the box through the hand holes and exposed that little bit.
You can see from the pattern that the film had not been fed exactly straight into the rollers.
Key Points
Please take a moment to review these points, reflect on their significance, and consider how they apply to your own experiences.
Tick to confirm (optional):
- Light contamination in automatic processors can cause specific patterns of light and dark areas on a film.
- If wrist-holes in the dark box are too large, light may enter during film unwrapping, leading to dark areas where light reaches the film.
- Removing hands from the dark box too early, before the film fully enters the developing compartment, can expose the remaining film to light, creating patterns of light and dark on the image.