1. Collection Care:
Environmental Factors
Part II: Light
Valinda S. Carroll
2008

2. Effects of Light
Light is necessary for exhibits, but excess
exposure can lead to many problems
 Fading
 Yellowing
 Weakening and breakage of fibers and
polymers

3. Light Monitoring Tools
 Blue Wool standard
 Light meter
 UV meter
 Light data logger

4. Blue wool
Advantages
•Blue wool swatches provide a qualitative
assessment of fading.
•They are compact and portable enough to use
in frames or exhibit cases.
•A spectrophotometer or colorimeter may be
used to detect blue dye fading before it
becomes visible to the human eye.

5. Blue wool
Disadvantages
•Blue wool standard swatches only show fading;
they cannot indicate future fading or other types
of damage.
•The extent and rate of fading vary depending
on the spectrum of the light source. Blue wool
standards were designed for use with sunlight,
not artificial lights.

6. Light Meter
Advantages
•Can measure output from
windows and lamps
•Can measure incident light
falling on surface of object
•Portable
•Can be read instantly
•Can show lux or foot-
candles
(1 foot-candle~ 10 lux)

7. Light Meter
Disadvantages
•Does not generate
permanent record
•Requires batteries

8. Ultraviolet radiation
The upper limit of 75 microwatts per lumen is maximum
recommended level of ultraviolet radiation (UV), based on
conventional incandescent light bulbs. Typical halogen and
fluorescent lights produce high UV levels, so they must be
filtered. Sunlight generates high levels of ultraviolet and
visible light, so windows must be covered with shutters,
window treatments, or filtering film. Fiber optic exhibit
lighting usually contains a built-in UV filter.

9. Ultraviolet Meter
Ultraviolet radiation is expressed relative to the overall light level in lux. The
maximum recommended amount of UV is 0.375 microwatts per square centimeter,
measured at a light level of 50 lux (about 5 foot-candles).
Ultraviolet (UV) meter showing
9 microwatts per square
centimeter, a rather high level.

10. UV-filtering materials
Ultraviolet filtering materials can
be used in windows, light
fixtures, exhibit cases, and/or
frames
•Acrylic (Plexiglas UF, Acrylite
OP, TrueVue Optium)
•Polycarbonate (Lexan)
•Laminated Glass (Schott
Amiran)
•Filtering window films
•Fluorescent tube sleeves

11. Exposure Limits
Light exposure limits vary according to the duration of
the exposure. The reciprocity rule dictates that a brief
exposure at a high level is the same as a longer
exposure at a low light level. This exposure is
expressed in lux-hours or foot-candle-hours.
Some light-induced chemical reactions may continue
in the dark (free radical reactions). This is why high
light levels of short duration can cause more damage
to light-sensitive items than low light levels of longer
duration.

12. Mitigation Strategies
 Store collections in closed boxes and
cabinets, rather than open shelves
 Close shutters (in historic buildings),
shades, or blinds
 Use UV-filtering glazing in frames
and exhibit cases and UV-filtering
sleeves on lights
 Hang curtains in front of vulnerable
artwork or drape cloth over exhibit
cases when museum is closed
 Use motion detector switches for
gallery lighting

13. End of Part II
Proceed to Part III