Guideline 15.6

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== Guideline 15.6: Design strategies are used to enhance visibility without increasing light exposure ==
=== What design strategies can enhance exhibit visibility? ===
In addition to utilizing controls and hardware to reduce, redirect and block light, the designer can also employ design strategies to enhance visibility in the exhibit space and help the visitor adjust to lower light levels:
* Use a gradual rather than an abrupt transition between differently lit areas to make objects visible at low, restricted light levels. Separate bright public access areas from display areas, and provide adaptation paths between the two. The human eye needs time to adjust from bright to low light. As visitors approach an exhibit area, the light levels to which they are exposed will influence their response to lower light levels inside the exhibit space. 
* Group light-sensitive objects away from exhibit entrances and points of bright light such as windows. 
* Use colors to enhance object visibility: The color of a wall or case interior, its texture, and its intensity of hue can affect the visibility of objects on display. Avoid sharp contrasts, because any juxtaposition of light and dark will lower viewing comfort. 
* Use lamps of the appropriate Color Rendering Index (CRI) value: Choosing a lamp with the appropriate CRI allows lower wattage without lowering visitor comfort. This is because the type of light influences a viewer’s color perception of an object. In general, most exhibit lighting plans try to achieve a color rendering close to daylight. 
* Provide separate lighting for Non-exhibit activities: Create separate circuits and controls for task-specific lighting. Controls for security checks, exhibit cleaning and maintenance, and object installation should be separate from controls to illuminate the objects, graphic panels, and other exhibit elements.
=== How can the Color Rendering Index be used to enhance exhibit visibility? ===
Industry uses the Color Rendering Index (CRI) to rate a lamp’s ability to accurately represent colors. The reference point is outdoor daylight with a CRI of 100. The closer to 100 the CRI is, the more balanced the light color. Some lamps produce cool or blue light, while others produce a warmer or yellow light.
In general, simply dimming the lights can be a critical design mistake. This usually causes a shift in the color rendering toward the warmer end of the light spectrum, making the human eye perceive the amount of light as even dimmer than the measurable level would indicate.
To provide a lower light level without color distortions, choose a lamp with a lower wattage but a high CRI value and a moderate chromaticity value. The chromaticity values of lamps are rated according to color temperature (Expressed in degrees Kelvin or °K):
* Lamps of around 3500°K are considered more moderate in tone and produce a white light. They are usually desirable for museum lighting purposes.
* Lamps with a value of 3000°K and lower provide “warm” light that accentuates reds and yellows.
* Lamps of 4000°K or higher produce a “cool” tone that gives an overall blue-green cast.