PC Light

all done everything

photon energy in UV vs visible vs IR light

highest with UV light

boundary between UV and visible light

400nm

unit of light

nm - nanometers (wavelength scale)

photon energy units

eV - electron volts

at what eV do you get yellow by-products

UV - >= 3 eV

what eV does colorant fading happen at?

between 2 and 3 eV

lux descr

log scale of light intensity, amount of light on a surface

scotopic def

night vision

photobic def

color vision

what is the rate of light damage proportional too

intensity

lumen def

amount of light emitted by a light source per second in all directions

dose of light on a surface - formula + unit

light intensity (lux) x time (hours) (final unit in millions of lux hours - mlx h (mega lux hours))

how do you measure UV?

relative to intensity of light - in microW/lm (units of microwatts (of UV) per lumen)

how do you measure IR

paint a thermometer bulb matt black (similar to measuring feels like temperature)

illumination standards

10-200 lux - orientation lighting (can also be for sensitive objects in museums)
200-800 lux - work light (eg offices)
800-3,000 lux - lighting for special work (typically locally applied with eg a torch)

total lux needed for an elderly person looking for subtle patterns in fine detail in a dark object

up to 4,000 lux

CRI def

color rendering index - measures light quality in terms of viewers ability to see colors correctly (often minimum of 85 needed)

what sort of light is high color temp vs low color temp

high color temp - cool light
low color temp - warm light

deterioration by UV (4)

yellowing, chalking, weakening and/or disintegration of materials

deterioration by IR

heats up - becomes an issue of incorrect temperature

4 categories of sensitivity to light (according to CCI)

none, low, medium, high

example for each light sensitivity level

none: most mineral pigments
low: ISO blue wool 7, 8 or higher, “permanent” artists palettes
medium: ISO blue wool 4, 5 or 6, alizarin dyes
high: ISO blue wool 1-3, most plant extracts

just noticable fade vs almost total fade

jnf - based on doses for the rage of ISO blue wools in that sensitivity category
almost total fade - based on conservative estimate of 30x the jnf BUT fading often slows down so for many 100x is more accurate

steps between ISO blue wools

each about 2-3 times as sensitive as the next

examples of diff materials sensitivity to UV

none: inorganic materials like metals/stone/glass
low sensitivity: crackling/chalking of modern plastics
medium: wood turns gray and erodes
high: chalking of oil paints with photosensitizing pigments
very high: yellowing of some low quality papers eg newsprint

with which 2 light sources does IR light become a problem?

incandescent lights at high intensity and direct sunlight

why we need light in museums (5)

to see, to be seen, to influence the observer’s view (emphasize certain elements in the exibition/create a specific atmosphere), “light objects” (objects with light incorporated), as signs (exit/directions/etc)

what rank is light in the 10 agents of deterioration

4

typical degradation reactions

light/oxygen/heat/moisture - often in combination, typically hydrolysis and oxidation

parameters of photo degradation - label red (6)

light source, oxygen, temp, catalyst, component, matrix

parameters of photo degradation - label orange - from light source (3), catalyst (2)

light source: intensity, time, wavelength
catalyst: type, loading - do not want it in your object eg titamium oxide - absorbs light very quickly and then spreads it to other objects

parameters of photo degradation - label orange - from component (2), matrix (2) + green

component: concentration, structure
matrix: solvent (type, pH), substrate (type, humidity, mordant/lakes)

issue with varnishes

can be more susceptible to damage - eg can yellow

through which process can plastic degrade

photo-oxidation

2 egs of degradation of polymers

yellow and brittle paper, degraded textile

what happens with molecule/atoms with diff types of radiation

UV - bond breaking and ionization
visible - electronic excitation
IR - vibration

when are UV and IR light used in museums

for object analysis

lux and lumen relation

1 lux = 1 lumen per square meter

when is the change from night vision to real vision

between 0.05 and 3 lux

rods & cones what does what

rods record light, cones record color

perception of color - humans

more sensitive to red light compared to blue

different zones where an object can be (4)

outside environment, building, room, showcase

wavelength and energy relation

the shorter the wavelength -the higher the energy (eg UV)

IR basic descr (4 points)

experienced as heat, weakens thermo-plastic materials (eg wax, plastics), accelerates chemical deterioration, increasing temperature will lower relative humidity (eg in a show case)

current guidlines for light exposure

light budget - dose matters, eg 50.000 lux hours is 1000 hrs at 50 lux so 8 hours x 50 lux x 125 days

how can you measure light

lux meter

things to consider with lux when calculating dose (5)

think about light source: outdoor light, glass showcase, UV protection, light source itself (LEDs, fluorescent tube, halogen), dim light level, etc

things to consider with time when calculating dose (5)

think about exposure time: opening hours, only light in presence of visitors, exchange objects?

what were the ISO blue wool exposed as

120 Mlux (inc. UV)

jpc - when

just perceptible change - at deltaE = 1.5

measures against UV (4)

avoid direct sunlight, filter UV from (sun) light, close curtains, select UV free light sources

measures against visible light (2: 4, 3)

reduce intensity: role up curtains, increase distance between object and light source, lamp w/ lower energy, grey filter in front of the light source
decrease exposure time: light only during opening hours, rotate the object regularly, use time switches/sensors reacting on movement

measures against IR (5)

increase distance between object and light source, use shutters on the south side of the building, use (roll up) curtains or foil on the inside, keep light sources outside the showcase, use cold reflector lights/glass fiber/LED

selecting a light source : from two perspectives (3:4)

from preventative persp: low intensity, no UV, low in temo
from exibition persp: good visibility, color temp, color rendering, costs (energy/life span)

what sort of light is a sodium lamp

warm

3 types of lamps

incandescent (low UV, high IR), fluorescent (very spiky wavelength - differs), LED (sorta bell curve of wavelength)

tungsten and halogen lamp descr

not for sale anymore for environmental reasons, can be replaced by energy saving lamps, releases a lot of IR

fluorescent tube (4 points)

color rendering depends on type, higher initial costs, lower energy consumption, longer life span

glass fiber optics (3 points)

light source is halogen/metal halide/LED, no UV, no heat

what to do if you cannot avoid light

remove oxygen - eg create an anoxic showcase

with what other aod can light combine

heat, moisture can produce accelerated hydrolysis with light

why is light high up in priority in the AoD

a lot can be done to prevent damage from it