Lighting Control Options: Dimmers, Films, Filters

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Options to protect collections against light damage include dimmers that limit the time objects are exposed to light and filters and films that reduce the total amount and type of radiation.

What are some options for lowering the amount of light exposure for sensitive collections?

Control of light levels is a complex issue that requires careful and comprehensive planning. The choice of a lighting system is the most critical decision. The amount of light output can be further controlled by connecting a lamp to a dimmer that lowers its output, or by placing a film or filter between the lamp and subject being viewed.

• Dimmers provide rheostat control of the amount of light generated by a lamp. These are often installed at the control source of all the lights (switch), but are more effective if installed on individual fixtures that will illuminate sensitive objects. Dimmers can reduce the amount of light output down to 50% (note- a shift in color rendering will occur).
• Films produced for theatrical productions and those used to control UV, visible and IR radiation passing through architectural glass can be used to lower the amount of radiation in some exhibit situations. These films are placed between the light source and the viewing area.
• Filters block the total amount of light that passes through the material. Mini-louvered blinds, woven synthetic fabrics, and plastic and metal scrim materials have been used successfully in exhibits. These products can be used directly on case glazing or cut to fit into holders on individual lamps, or placed between the display and lighting chambers. If located close to lamps, plastic materials and the coatings on metal scrims must be researched to ensure inflammability and that no outgassing or other problems will be caused by exposure to elevated heat.

How are dimmers used in exhibit areas?

Interest in energy conservation has lead to more reliable and sensitive light dimming products. Dimmers can be used to control the light: (1) in an overall exhibit space; (2) falling on a particular object within that space; or (3) within an individual exhibit case. A dimmer is a particularly good choice in areas of relatively little activity or where visitation fluctuates seasonally. Dimmers can be used to raise light levels in a gallery in advance of visitor traffic. Many situations can be satisfied with the use of domestic-type dimmers; some require commercial dimming controls. Some design options include:

• Light level: Dimmers may be set permanently to illuminate at a pre-determined light level; or may be programmed to increase the light output in response to an activation signal such as a lowering in ambient light levels or visitor request.
• Dimmers can be visitor operated, in which the visitor pushes a button to increase light; ultra- sonically controlled, in which movement activates the dimmer; or trigged by body heat or sound.1
• Sensor location: Sensors may be located in the ceiling, wall, or floor. In addition, a photoelec- trically controlled beam can be aimed across a pathway. False signaling can occur if the sensor is poorly located, for example in the air flow from a HVAC duct.
• Timer control: A timer can be set to turn the lights off or lower light levels after a pre-deter- mined amount of time or after a pre-determined length of inactivity in the space.
• Sensitivity: The amount of motion, or other triggering mechanism, needed to activate the sensor is important. Sensors of different sensitivity are available and a few can be set for individual applications.
• Coverage: Sensors are available to cover both small and large areas.
• Compatibility: Dimmers are compatible with all incandescent lamps; more care is needed when choosing a dimmer for a fluorescent lamp. Lamp life may be shortened by use of a dimmer.
• Override: An override ability is desirable for special situations.

It is important to note that dimming a lamp usually shifts its color rendering index (CRI) towards the warmer end of the light spectrum. The lower light level, in turn, is perceived to be even dimmer. Choosing a lamp with a lower wattage, but with a high CRI value and a moderate chromaticity value will provide a lower light level without color distortions. Lamp manufacturers and distributors usually offer technical advice for use of their products; also consult a lighting designer or engineer.

1 Green Seal’s Choose Green Report “Occupancy Sensors”.(February 1997): 1-7.

Products, Manufacturers, and Suppliers

Mention of a product, manufacturer, or supplier by name in this publication is for information only and does not constitute an endorsement of that product or supplier by the National Park Service. Listed materials have been used successfully in past applications. It is suggested that readers also seek alternate product and vendor information to assess the full range of available supplies and equipment.

Dimmers

• Leviton MFG
• MyTech Corporation
• Sensor Switch Inc.
• Technology Design Center, Inc.
• The Wattstopper

Theatrical Films, Textured, Tinted

• ROSCO