After recently helping to light a live broadcast from inside Buckingham Palace’s State Rooms, I was curious to read up and do some research into how lighting for film and TV can affect paintings. My findings will help to determine what equipment would best be suited to such a shoot so the lighting doesn’t have any lasting damage on the paintings.
How lighting affects materials
Photodegradation is where material colours fade from their exposure to light. Colours are seen because of the way a material absorbs light, the un-absorbed light is reflected, and this is the colour we perceive the object. In the electromagnetic spectrum, visible light waves (from about 390nm to 700nm wavelength) is less harmful to sensitive materials because of its lower frequency compared to other electromagnetic waves.
Ultraviolet rays have a higher frequency, so can be described as having more energy than visible light. When absorbed by the paint or colour on an artwork, this can “break down the chemical bonds and thus fade the color(s) in an object – it is a bleaching effect. Some objects may be more prone to fading, such as dyed textiles and water-colours. Other objects may reflect the light more, which makes them less prone to fade” (Everyday Mysteries, http://www.loc.gov/rr/scitech/mysteries/colors.html , website).
There are numerous factors that can change how light will affect an artwork such as the intensity of the light, how long the light is on for and what the material of the artwork is.
From researching through the various sources below, all evidence points towards using LED based light sources where delicate artworks are to be lit. This is because of their very minimal UV emission and low heat output. Although if used for short periods of time, incandescent tungsten fixtures can be used because they also have low UV emission, but the heat generated from their use is significantly higher.
Hydrargyrum medium-arc iodide lamp (HMI) fixtures emit a larger quantity of UV radiation, however the lens of the fixture is made from glass, which allows visible light to pass through it without absorption, but filters ultraviolet light of shorter wavelengths out. An edition to the rig would be to add UV filter gel. This can be added in front of the light source to reduce the UV emissions that penetrate the filter. The Rosco filter linked allows less than 10% transmission below 390 nanometers. Even with this prevention method, HMI fixtures should be used with extreme caution, if at all, around sensitive pieces.