ASTM E1733-22

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1733 − 22
Standard Guide for
Use of Lighting in Laboratory Testing
This standard is issued under the fixed designation E1733; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.3 Special needs or circumstances will dictate how a given
lightsourceisconstructed.Thisisbasedontherequirementsof
1.1 The use of artificial lighting is often required to study
the test and the environmental compartment to which it is
the responses of living organisms to contaminants in a con-
targeted. Using appropriate conditions is most important for
trolledmanner.Evenifthetestorganismdoesnotrequirelight,
any experiment, and it is desirable to standardize these condi-
the investigator will generally need light to manipulate the
tionsamonglaboratories.Inextremecases,testsusingunusual
samples, and the test might be conducted under the ambient
lighting conditions might render a data set incomparable to
light of the laboratory. One will need to consider not only
other tests.
whether the particular test organism requires light for growth,
but also whether the environmental compartment relevant to
1.4 The lighting conditions described herein are applicable
thetestisexposedtolightand,ifso,whattheattributesoflight
to tests with most organisms and using most chemicals. With
are in that compartment. The light could affect growth of the
appropriate modifications, these light sources can be used
organism or toxicity of a contaminant, or both. For instance, it
under most laboratory conditions with many types of labora-
has been shown that the toxicity of some organic pollutants is
tory vessels.
enhanceddramaticallybytheultraviolet(UV)radiationpresent
2 1.5 The attributes of the light source used in a given study
insunlight (1, 2). Furthermore,thelevelofambientlightingin
shouldlistthetypesoflampsused,anyscreeningmaterials,the
thelaboratory(whichmightaffectthetest)isnotstandardized,
−2
light level as an energy fluence rate (in W m ) or photon
nor is it comparable to natural environments. It is thus
−2 −1
fluencerate(inµmolm s ),andthetransmissionproperties
important to consider lighting in all forms of environmental
of the vessels used to hold the test organism(s). If it is relevant
testing. When light is used in the test, one should determine
to the outcome of a test, the spectral quality of the light source
whetherthespectraldistributionoftheradiationsourcemimics
shouldbemeasuredwithaspectroradiometerandtheemission
sunlightadequatelytobeconsideredenvironmentallyrelevant.
spectrum provided graphically for reference.
Also, the container or vessel for the experiment must be
transparent, at the point of light entry, to all of the spectral
1.6 The sections of this guide are arranged as follows:
regions in the light source needed for the test.
Title Section
Referenced Documents 2
1.2 It is possible to simulate sunlight with respect to the
Terminology 3
visible:UV ratio with relatively inexpensive equipment. This
Summary of Guide 4
Significance and Use 5
guide contains information on the types of artificial light
Safety Precautions 6
sources that are commonly used in the laboratory, composi-
Lamps 7
tions of light sources that mimic the biologically relevant
Artificial Lighting 7.1
Light Sources 7.2
spectralrangeofsunlight,quantificationofirradiancelevelsof
Construction of Artificial Light Sources that Mimic Sunlight 8
the light sources, determination of spectral outputs of the light
Sunlight 8.2
sources, transmittance properties of materials used for labora-
Visible Light 8.2
Visible Light Plus UV-B Radiation 8.3
tory containers, calculation of biologically effective radiation,
Simulated Solar Radiation 8.4
and considerations that should go into designing a relevant
Transmission Properties of Lamp Coverings and Laboratory Vessels 9
light source for a given test.
Lamp Coverings 9.2
Laboratory Vessels 9.3
Measurement of Light 10
Light Components 10.1
Measurement of Light Quantity 10.2
ThisguideisunderthejurisdictionofASTMCommitteeE50onEnvironmental
Spectroradiometry 10.3
Assessment, Risk Management and CorrectiveAction and is the direct responsibil-
Biologically Effective Radiation 11
ity of Subcommittee E50.47 on Biological Effects and Environmental Fate.
Considerations for Designing Light Sources for Environmental Testing 12
Current edition approved Aug. 1, 2022. Published September 2022. Originally
approvedin1995.Lastpreviouseditionapprovedin2014asE1733–95(2014).DOI:
1.7 The values stated in SI units are to be regarded as the
10.1520/E1733-22.
standard. The values given in parentheses are for information
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this guide. only.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1733 − 22
1.8 This standard does not purport to address all of the referred to as light intensity, although this is not a desirable
safety concerns, if any, associated with its use. It is the term because intensity refers to the amount of radiation in a
responsibility of the user of this standard to establish appro- unit angle. The energy fluence rate (also irradiance, energy
−2 −1
priate safety, health, and environmental practices and deter- flow rate, or power) is usually given in units of J m s orW
−2 −1
mine the applicability of regulatory limitations prior to use. m (1Js =1 W). The photon fluence rate (flow rate on a
−2 −1
Specific precautionary statements are given in Section 6. quantumbasis)isusuallygivenintheunitµmolm s .(This
−2 −1
1.9 This international standard was developed in accor- is equivalent to µEinstein m s . An Einstein is Avogadro’s
dance with internationally recognized principles on standard- number (a mole) of photons and was used for quantum
ization established in the Decision on Principles for the measurements but is no longer an SI — supported unit (see
Development of International Standards, Guides and Recom- IEEE/ASTM SI 10 ).) The conversion between energy fluence
mendations issued by the World Trade Organization Technical rate and photon fluence rate is as follows:
Barriers to Trade (TBT) Committee. 22 21 22 23
µmolm s 5Wm 3 λ nm 38.36 310 (1)
~ !
3.2.2.1 Discussion—This illustrates an inherent problem of
2. Referenced Documents
converting between light units: the energy is wavelength (λ)
2.1 ASTM Standards:
dependent, so conversion between energy and quantum units
E943Terminology Relating to Biological Effects and Envi-
requires knowledge of the spectral distribution of the light
ronmental Fate
source (see 10.2.4 for conversion guidelines).
E1218Guide for Conducting Static Toxicity Tests with
3.2.3 fluorescence, n—emission of light by an excited atom
Microalgae
or molecule.
E1415Guide for Conducting Static Toxicity Tests With
4 3.2.4 foot-candle, n—lumen per ft (see 3.2.8).
Lemna gibba G3 (Withdrawn 2021)
3.2.5 frequency (ν), n—description of radiation as the num-
E1598Practice for Conducting Early Seedling GrowthTests
ber of wave peaks passing a point in space per unit time. Units
(Withdrawn 2003)
−1
are normally cycles s or Hz.
IEEE/ASTM SI 10 Standard for Use of the International
System of Units (SI): The Modern Metric System
3.2.6 IR, n—infrared radiation (wavelength range, 760 nm
to 2000 nm).
3. Terminology
3.2.7 irradiance, n—quantity of radiant energy received by
3.1 Definitions—The words “must,” “should,” “may,”
aunitareaperunittime.Thisisthesameastheenergyfluence
“can,” and “might” have very specific meanings in this guide.
rate.
“Must” is used to express an absolute requirement, that is, to
3.2.8 lumen, n—light emitted by a point source of 1 cd. It is
state that the conditions ought to be designed to satisfy
a unit of luminosity or brightness used in photography and
appropriate lighting, unless the purpose of a test requires a
stage lighting and is irradiance based on sensitivity of the
differentdesign.“Must”isonlyusedinconnectionwithfactors
human eye (maximum sensitivity at 550 nm). It has the same
that directly relate to the acceptability of specific conditions.
dimensions as watts because it is equivalent to irradiance by
“Should” is used to state that a specified condition is recom-
definition. However, the lumen as a measurement is wave-
mended and ought to be met if possible.Although violation of
length dependent (1 lm at λ 560 nm is 1.5 mW, and 1 lm at λ
one“should”israrelyaseriousmatter,violationofseveralwill
430 nm is 127 mW) (see 10.2.3), so extreme care should be
oftenrendertheresultsofatestquestionable.Termssuchas“is
used with this unit. If possible, light levels based on lumens
desirable,” “is often desirable,” and “might be desirable” are
should be converted to an appropriate light unit for environ-
used in connection with less important factors. “May” is used −2 −2 −1
mental studies (for example, W m or µmol m s ) (see
to mean is (are) allowed to, “can” is used to mean is (are) able
10.2.4 for conversion guidelines).
to,and“might”isusedtomeancouldpossibly.Thustheclassic
3.2.9 lux, n—lumen per m (see 3.2.8).
distinction between may and can is preserved, and might is
3.2.10 photon, n—one quanta (or single indivisible packet)
never used as a synonym for either “may” or “can.”
of light or radiant energy. A mole of photons (an Einstein)
3.2 Descriptions of Terms Specific to This Standard (see
equals Avogadro’s number (6.022×10 ). The energy of a
also Terminology E943):
photonisrelatedtoitsfrequencyorwavelengthandisgivenby
3.2.1 fluence, n—amountoflightperunitarea,expressedas
−34
−2 −2 E= hν= hc/λ, where h=planks constant (6.6×10 J s),
energy (J m ) or photons (mol m ). This is sometimes
8 −1
c=speed of light (3×10 ms ), ν=frequency, and λ
equated to light dose.
−1
=wavelength (if c is used in m s , then λ must also be in m).
3.2.2 fluence rate, n—flow rate of light, flux of light, or the
3.2.11 spectral distribution, n—a description of a light
amount of light per unit area per unit time. It is sometimes
source as the quantity of light at each wavelength. An energy
spectral distribution is the energy of a light source given as a
function of wavelength. A photon spectral distribution is the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
number of photons in a light source as a function of wave-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
length.
the ASTM website.
3.2.12 UV-A, n—ultraviolet A radiation (wavelength range,
The last approved version of this historical standard is referenced on
www.astm.org. 320 nm to 400 nm).
E1733 − 22
3.2.13 UV-B—ultraviolet B radiation (wavelength range, 6.2 Ozone—Many UV light sources (those emitting UV-C)
290 nm to 320 nm). produce ozone. For instance, xenon (Xe) arc lamps produce
significant amounts of ozone. Adequate ventilation should be
3.2.14 UV-C, n—ultraviolet C radiation (wavelength range,
provided to remove the ozone.
200 to 290 nm).
6.3 Ultraviolet Radiation—Any light source producing
3.2.15 visible light, n—thespectralregionvisibletohumans
UV-B or UV-C is harmful to eyes and skin. In particular,
(wavelength range, 400 nm to 700 nm). This is the photosyn-
contact with eyes is to be avoided, even for very short periods
thetically active region of the spectrum as well.
oftime.Eyescanbeshieldedwithappropriateeyeware(safety
3.2.16 wavelength (λ), n—the description of radiation (or
glasses or goggles that absorb UV radiation) available from
radiant energy) as the distance between two consecutive peaks
most scientific supply companies. The spectral quality of the
in an electromagnetic wave. Units are normally in nm. The
eyeware should be checked periodically with a UV/vis spec-
energy of a photon is inversely proportional to its wavelength.
trophotometer. Transmission should be less than 0.1% for all
Also, frequency×wavelength=speed of light.
wavelengths below 330 nm. Contact with skin is also to be
prevented.Ingeneral,alllightsourcesthatgenerateUV-Bwill
4. Summary of Guide
generate some UV-C as well.
4.1 This guide provides information on several types of
6.4 Heat—Many light sources, especially short-arc lamps,
laboratory light sources and the need for standardized lighting.
create a high fluence rate of IR radiation. Skin, clothing, and
The varieties of commercially available light sources and the
other materials exposed to high levels of IR radiation are
spectralqualityoftheiroutputsarepresentedfirst.Thewaysin
subject to severe burns or may ignite.
which different lamps can be assembled to mimic sunlight are
6.5 Warning—Mercury has been designated by EPA and
then summarized. There is a discussion of the methods for
many state agencies as a hazardous material that can cause
measuring the amounts and spectral quality of light, and the
central nervous system, kidney and liver damage. Mercury, or
need for accurate standardized methods. Finally, a discussion
its vapor, may be hazardous to health and corrosive to
on biologically effective radiation is included.
materials.Cautionshouldbetakenwhenhandlingmercuryand
mercury containing products. See the applicable product Ma-
5. Significance and Use
terial Safety Data Sheet (MSDS) for details and EPA’s website
5.1 The information in this guide is designed to allow
– http://www.epa.gov/mercury/faq.htm - for additional infor-
investigators conducting research or tests of environmental
mation. Users should be aware that selling mercury and/or
relevance to select appropriate light sources.
mercury containing products into your state may be prohibited
by state law.
5.2 Investigators will be able to make reasonable selections
of light sources based on cost, the requirements of the test
7. Lamps
organisms, and the properties of the test chemicals.
7.1 Artificial Lighting—The development of artificial light-
5.3 Thesemethodshavemajorsignificanceforthecompari-
ing stems from two needs: (1) the requirement for inexpensive
son of results between laboratories. Investigators at different
commercialandpubliclightingand(2)specializedlightingfor
sites will be able to select similar light sources. This will
research and technology (see Table 1 for a listing of some of
provide standardization of a factor that can have major impact
thelightsourcesavailable).Thereareessentiallytwowaysthat
on the effects of hazardous chemicals.
lightcanbegeneratedfortoxicitytesting:(1)electricdischarge
lamps, those that are based on photon emission from an
6. Safety Precautions
electronically excited gas (for example, fluorescent and short-
arc lamps); and (2) thermal lamps, those that are based on
6.1 Many materials can affect humans adversely if precau-
photon emission from a heated filament (for example, incan-
tions are inadequate. Therefore, eye and skin contact with
descent lamps) (12, 13). Laser sources are not practical for
radiation (especially UV) from all light sources should be
most toxicology studies and are not discussed in this guide.
minimized by such means as wearing appropriate protective
eyeware, protective gloves (especially when washing equip- 7.2 Light Sources:
mentorputtinghandsintestchambersorsolutions),laboratory
7.2.1 LED Lamps—Light-emitting diode (LED) lamps are
coats, and aprons. Special precautions, such as enclosing test composed of diodes made of semi-conductive materials, such
chambers and their light sources, and ventilating the area as silicon or selenium, that contain two electrodes (an anode
surrounding the chambers, should be taken when conducting andcathode)thatproducelightuponintroductionofanelectric
tests. Care should be taken when using light measuring current. Heat produced by LED lamps is absorbed into a heat
equipment to prevent the accidental breakage of light sources sink, which prevents performance issues and also any heat
into test vessels to ensure organism health. Information on issues for users. LED lamps are more efficient than incandes-
toxicity to humans (3-5), recommended handling procedures cent and fluorescent lamps, and they are also directional,
(6-8), and chemical and physical properties of the test material meaningtheyemitlightinaspecificdirectionincomparisonto
and light source should be studied before a test has begun. incandescent and fluorescent lamps which produce light and
Special procedures might be necessary with UV light sources, heat in all directions. They do not typically ‘burn out’ or fail
radio-labeled test materials, and materials that are, or are like incandescent or fluorescent lamps. Instead, ‘lumen depre-
suspected of being, carcinogenic (9-11). ciation’occurs, and the lifetime of an LED light is considered
E1733 − 22
TABLE 1 Light Sources
254 nm (that is, in the UV-C). The 254nm photons are
B
Approximate Cost absorbed by a phosphor coating on the inside of the tube, and
Spectral Fluence Manufac-
Lamp
A C
D
Regions Rate turers
Lamp Fixture thephosphoremits(fluoresces)atlongerwavelengths(280nm
E,F,G
Fluorescent visible 20–400 5–20 10–30 to750nm).Thespectraloutputofthelamp(Figs.3and4)will
H,I
UV-A 1–50 10–40 10–30
thus depend on the composition of the phosphor coating. The
H,I,J
UV-B 1–50 10–40 10–30
H most common phosphors are halophosphates, for instance,
UV-C 1–50 10–40 10–30
K
visible + UV-A 20–400 20–50 10–30 barium titanium phosphate, manganese-activated magnesium
Short-arc
gallate, and calcium halophosphate, which emit mostly in the
L,M,N
Hg UV-B, UV-A, 500–2000 150–1000 2000–6000
visible region of the spectrum. Many different types of fluo-
visible
L,M,N,O
Xe UV-B, UV-A, 500–2000 150–1000 2000–6000
rescent lamps are commercially available (Table 1).The major
visible
benefitsoffluorescentlampsaretheavailabilityofinexpensive
K
Metal halide UV-A, visible 300–1000 100 1000
K
fixtures and bulbs, low heat (IR) output, long life, and stable
Sodium visible 300–1000 100 1000
vapor
spectral quality. However, the irradiance levels of fluorescent
P,Q
Microwave UV-B, UV-A, 500–2000 2000 10000
lamps are relatively low; it is difficult to build a fluorescent
visible
−2
E,F,G
lighting system with more than approximately 400 µmol m
Incandescent visible 100–1000 5–100 10–1000
−1
E,F,G
LED UV-C, UV-B, 4-10 10-30 s (only approximately 20% of full sunlight). Most fluores-
UV-A, visible
cent light sales will be banned by 2020 as per the United
A −2 −1
In µmol m s .
Nations Environment Program Minamata Convention (16).
B
In U.S. dollars (in 1994).
C
7.2.2.1 Visible Light Fluorescent Lamps—The most com-
These are representative manufacturers but are by no means the only manu-
facturers. This listing should in no way be considered an endorsement.
mon is the cool-white fluorescent type, with a blue light
D
Power supply and lamp holder.
E (450-nm)toredlight(600-nm)ratioof1to2onaphotonbasis
General Electric; this company markets through local electrical suppliers.
F
(Fig. 3). Two other common types of fluorescent lamps are
Philips; this company markets through local electrical suppliers.
G
Westinghouse; this company markets through local electrical suppliers.
warm-white, with a higher relative level of red light, and
H
Southern New England Ultraviolet Co., Brantford, CT, 203-483-5810.
I daylight,withahigherrelativelevelofbluelight(Fig.3).Also,
Local theatrical lighting suppliers.
J
National Biological Corp., Twinsberg, OH, 216-425-3535. lamps with more balanced spectral distributions in the visible
K
Dura-Test Corp., Fairfield, NJ, 800-289-3876.
region are available (Table 1 and Fig. 3).
L
Oriel Corp., Stratford, CT, 203-377-8282.
M
7.2.2.2 Ultraviolet Fluorescent Lamps—UV fluorescent
Ealing Electro-Optics Inc., South Natick, MA, 617-651-8100.
N
Photon Technology Inc., South Brunswick, NJ, 908-329-0910.
lamps have phosphors that emit at approximately 300 nm
O
Heraeus DSET Laboratories, Inc, Phoenix, AZ, 602-465-7356.
(tanninglamp)and350nm(blacklight)(Fig.4).Low-pressure
P
Fusion Lighting, Rockville, MD, 301-251-0300.
Q
Hutchins International Ltd, Mississauga, Ont., 416-823-8557. Hg lamps without a phosphor are also available (germicidal
lamps). They emit a sharp line at 254 nm and are used in
laminar flow hoods and clean rooms to sterilize surfaces prior
to use. All of these UV fluorescent lamps are quite common
complete when the brightness of the LED lamp depreciates by
and are available from numerous manufacturers (Table 1).
30% or more. Common LED colors are red, green, and blue,
7.2.3 Metal Vapor Arc Lamps—Thebasisofshort-arclamps
with white light produced using a combination of different
is similar to fluorescent lamps, except that a phosphor is not
colored LED lights and/or a phosphor material that converts
required. The gas in the lamp is excited by a high electric
the light color to white. The LEDs generate narrow-banded,
potential. The gas then completes a direct current (dc) circuit
spatially uniform light at five wavelengths (275nm, 309nm,
between a cathode and an anode by forming an arc. As the
348nm, 369nm, and 406 nm), with irradiances that are stable
gaseous atoms in the arc relax to ground state, they emit
and easily adjusted to desired levels (Fig. 1 and Fig. 2). Initial
radiation.The two most common gases used are mercury (Hg)
investment in LED can be more expensive than other lamps,
and Xenon (Xe). These lamps have very high outputs, with
but the cost savings over time and longevity ultimately make
photon fluence rates in the visible spectral region exceeding
them a less expensive option. LEDs also have many advan-
−2 −1
2000 µmol m s . However, the lamps, lamp holders, and
tages over incandescent light sources, including lower power
stable high-voltage dc power supplies are generally expensive.
consumption, longer lifetime, improved physical robustness,
7.2.3.1 Mercury Short Arc Lamps—High-pressure Hg-arc
smallersize,andfasterswitching.Theyalsohaveawiderange
lampshavefivemajoremissionbands:at365nm,405nm,436
of controllable colour temperatures, wider operating
nm, 546 nm, and 578 nm (Fig. 5). In addition, they have a
temperature, no low temperature startup problems, and a low
lower-level emission that is a continuum from 280 nm to 800
maintenance cost. LEDs do not contain mercury and have a
nm. These lamps have very high outputs in the five main
low health impact as a result of low ultraviolet radiation (UV).
emission bands, without a great deal of IR. They can thus be
LEDs can very easily be dimmed either by pulse-width
veryusefulforspecificapplicationsinwhichhighfluencerates
modulation or lowering the forward current. This pulse-width
are required.
modulation is why LED lights, particularly headlights on cars,
when viewed on camera or by some people, seem to flash or 7.2.3.2 Xenon Short Arc Lamp—Xenon-arclampsemitwith
flicker. This is a type of stroboscopic effect. (14, 15). a great deal more lines than an Hg lamp.As such, this source
7.2.2 Fluorescent Lamps—Fluorescent lamps are based on provides a continuum of radiation from approximately 260 nm
excitationoflow-pressureHggasbyanelectriccurrent.When (UV-C) to 1100 nm (IR) (Fig. 5). In fact, Xe-arc lamps have a
the Hg atoms relax back to ground state, they emit photons at very close spectral match to sunlight. This, combined with a
E1733 − 22
FIG. 1 Spectral Outputs of LED Lamps: (A) Warm White; (B) Bright White; and (C) Daylight
E1733 − 22
FIG. 2 Spectral Output of LED lamp
FIG. 4 Spectral Output of UV Fluorescent Lamps: (A) UV-B
FIG. 3 Spectral Output of Visible Light Fluorescent Bulbs: (A)
Lamp; and (B) UV-A Lamp
Cool White; (B) Warm White; (C) Day Light; and (D) Color Classer
very high output and an ability to light relatively large areas, 7.2.3.3 Metal Halide Lamps—These are Hg arc lamps
makes this source highly attractive for environmental studies. doped with the halide salt of another metal. Iodine is the most
However, the amount of IR in the source can be problematic. common halide, and common metals are sodium, scandium,
Well-cooled chambers and appropriate IR filters might be thus dysprosium, and thallium. The presence of the mixed metal
required. vapors greatly increases the number of spectral emission lines
E1733 − 22
FIG. 6 Spectral Outputs of Metal Halide Lamps: (A) Sodium-
FIG. 5 Spectral Outputs of Short-Arc Lamps: (A) Hg Arc Lamp;
Scandium Lamp; and (B) Dysprosium-Thallium Lamp
and (B) Xe Arc Lamp
relative to Hg alone (Fig. 6). These lamps have high outputs mimic sunlight accurately in this spectral region (Fig. 8).They
and very good spectral distributions in the visible region, are also a focusable point source. Therefore, they are an
giving them an excellent “color” quality. The lamps also have excellent choice for many applications, especially plant
relativelyhighoutputsandlowIR.Theyarecommonlyusedin growth. Microwave lamps coincidentally have little IR, pre-
stadium and arena lighting for these reasons. They are a good venting most heat creation problems associated with high
alternative to Xe arc lamps for laboratory purposes. Also, the irradiance lighting.Also, they have little UV, and the addition
power supply for these lamps is an alternating current (ac) of these wavelengths to a test is thus at the choice of the
ballast, which is much less expensive than the dc power investigator. The bulb life for these lamps is very long,
supplies required for Hg and Xe short arc lamps. approximately10000h.Bulbscontainingpowdersofdifferent
composition that emit in the UV-B or UV-A have also been
7.2.4 Sodium Vapor Lamps—Low-pressure sodium (Na)
vapor lamps emit a sharp band at 589 nm (orange light) (Fig. developed. The only disadvantage at present with microwave
lamps is cost, due partly to the expense of new technology;
6). High-pressure Na vapor lamps also emit around at 589 nm,
but with a much wider emission band (approximately 100 nm) however, development is under way to bring down the cost.
(Fig. 7). Although these sources have limitations due to their 7.2.6 Incandescent Lamps—These lamps contain a solid
monochromatic nature, they are relatively inexpensive, they body(filament)thatisheatedbyanelectriccurrent.Theheated
can reach high fluence rates, and the light quality is near the filamentemitsinacontinuumwithaspectralqualitydescribed
peak wavelength for human vision. They are thus an excellent by the temperature of the filament.The higher the temperature
light source for street lighting. Although not necessarily the of the filament, the shorter the wavelengths that are emitted by
bestsourceforbiologicaltesting,especiallywhenplantgrowth the lamp (Fig. 9). The most common filament is tungsten; this
is involved, they are nonetheless used to achieve high fluence metal is strong, and has a high melting temperature and low
rates without heat problems. This is because orange light can vapor pressure at high temperature. This gives the filament a
be used reasonably efficiently for photosynthesis (17). long life. To minimize evaporation of the metal, the bulb is
7.2.5 Microwave-Powered Light Sources—An emerging generallyfilledwithinertandstablegases(suchas90%argon,
technology is the microwave-powered lamp, which work by 10% nitrogen). A small amount of a halogen gas (at approxi-
microwave excitation of an elemental sulphur powder inside a mately 1%) is often used as well (thus the name tungsten-
small spherical bulb. The microwave-excited sulphur emits halogenlamps);thiscausesevaporatedtungstentoredepositon
visible photons. These lamps have very high fluence rates in thefilament,furtherincreasingthelifeofthelamp(upto2000
the visible spectral region from 400 nm to 700 nm, and they h). The lamps have excellent light quality in the visible region
E1733 − 22
FIG. 9 Spectral Outputs of Incandescent Lamps
variable. For example, on a clear day in late summer, the
UV-B:visible ratio at latitudes corresponding to southern
Canada and the northern United States is approximately 0.5%
ofvisibleonaphotonbasis(Fig.10(A)),whiletheUV-Blevel
is much higher closer to the equator or at higher elevations; as
high as 1.5% of visible (19, 20).Also, the amount of UV-B is
increasing due to depletion of the stratospheric ozone layer
FIG. 7 Spectral Outputs of Na Vapor Lamps: (A) Low-Pressure
(21). The amount of UV-B varies with time of day, peaking at
Na Vapor Lamp; and (B) High-Pressure Na Vapor Lamp
solarnoon,andthefractionofUV-Binsolarradiationchanges
with season, exhibiting maximal levels around the summer
FIG. 8 Spectral Output of a Microwave Lamp
of the spectrum and have high outputs, but they also emit a
great deal of IR, which can create a heat problem.
8. Construction of Artificial Light Sources that Mimic
Sunlight
8.1 Sunlight—Radiation from the sun with wavelengths
FIG. 10 Spectral Distribution of Sunlight; a Visible Light Plus
greater than 290 nm can reach the surface of the earth (18).
UV-B Source and a SSR Source: Panel A, Sunlight Measured on
Radiationbelow290nmisabsorbedbythevariousgasesinthe
Cloudless Day on Lake Erie 23 Miles North of Cleveland, OH
atmosphereandisnotofenvironmentalconcern.Atthesurface
(12:21 p.m., 13 July 1994); Panel B, Emission Spectrum of a Vis-
of the earth, the molar ratio of visible:UV-A:UV-B is approxi-
ible Plus UV-B Source Filtered Through Cellulose Diacetate; and
mately 100:10:1; however, the content of UV-B is highly Panel C, SSR Source Filtered Through Polystyrene
E1733 − 22
solstice and minima around the winter solstice (19-22). One creates excess heat that is problematic to remove from envi-
should take these factors into consideration when designing a ronmental growth chambers, exposure chambers, and incuba-
laboratory light source that will mimic sunlight. tors.
8.4.1 Simulated Solar Radiation with Fluorescent Lamps—
8.2 Visible Light—Any of the light sources described above
One can construct a light source that mimics sunlight with
can be used if only visible light is required for a test. The best
respecttotherelativeamountsofvisibleandUV(avisible:UV-
choice is fluorescent lighting if low fluence rates are required.
A:UV-B ratio of 100:10:1; Fig. 10(C)) using fluorescent lamps
Theinvestigatorwillhavetobalancetheprosandconsofother
(1). One such SSR source contains two cool-white fluorescent
types of lamps for higher irradiance lighting. For example,
lamps, one 350nm fluorescent lamp, and one 300nm fluores-
sodium vapor lamps could be used if the full visible spectrum
cent lamp.The 300nm lamp is filtered through cheese cloth to
is not required. For the entire visible region, incandescent
bring the UV-B level down to 1% of visible. The light is also
lamps can be used to supplement fluorescent lamps as long as
filtered through cellulose acetate or polystyrene to remove all
the refrigeration or cooling system has enough capacity to
of the incident UV-C (200 nm to 290 nm). While the spectral
handletheexcessheat.Amicrowavelampwouldbeidealifthe
output shown in Fig. 10(C) does not replicate sunlight
budgetary resources are available.
precisely, the visible:UV-A:UV-B ratio corresponds approxi-
8.3 Visible Light Plus UV-B Radiation—Alight source with
mately to that of terrestrial sunlight in the 290 nm to 700nm
UV-B at approximately 1% of visible light on a photon basis
wavelength range from mid-spring to mid-fall in temperate
canbebuiltinexpensively(Fig.10(B)).ThisvisibleplusUV-B
latitudes corresponding to southern Canada and the northern
sourcecontainscool-whitefluorescentlamps(visiblelight)and
UnitedStates (18, 22).B.napus(canola),Spirodelaoligorrhiza
a UV-B fluorescent lamp (23). The radiation from the UV-B
(aduckweed),andLemnagibba(aduckweed)havebeenfound
lamp is filtered through cellulose diacetate (0.08 mm) to
to grow well under this source, exhibiting no overt signs of
remove extraneous UV-C (<290 nm) (24); the Hg gas in
UV-B stress. The UV-B content of the source can be raised to
fluorescent tubes emits at 254 nm, and this UV-C radiation is
simulate ozone depletion by removing successive layers of the
not quantitatively removed by the glass and phosphor in UV-B
cheese cloth.
lamps. UV-C is much more damaging to biological molecules
8.4.2 Simulated Solar Radiation with Fluorescent and In-
than UV-B and must be quantitatively removed unless the
candescent Lamps—Onecanbuildalightsource,asin8.3,but
investigator is interested specifically in the effects of UV-C.
obtain a better spectral balance in the blue and red regions by
The UV-B lamp also can be screened with cheese cloth to
adding incandescent lamps. This can also increase the total
achieve the desired visible:UV-B fluence ratio. To mimic loss
fluence rate of the source.The other adjustment that should be
of the ozone layer, the UV-B level can be raised by removing
madeistoraisetheUVlevels,sothattheUV-BandUV-Awill
successive layers of cheese cloth from the UV-B lamp or
stillbeat1%and10%ofvisible,respectively.Onemightalso
adding extra UV-B lamps. It has been found that many plants
need to control the heat reaching the sample with refrigeration
(for example, B. napus (canola), rye, soybean, and L. gibba (a
systems or IR filters.
duckweed)) can be grown under a visible/UV-B source similar
8.4.3 SimulatedSolarRadiationwithaXenonArcLamp—A
to that described above (1, 23, 25-28). However, this type of
Xe arc lamp can be used alone to mimic solar radiation. One
lamp arrangement will have relatively low fluence rates (<400
simply uses a cut-off filter (such as Schott WG300; >90%
−2 −1
µmolm s ofvisiblelight).Someplants(forexample,peas)
transmittance above 310 nm, 50% transmittance at 300 nm,
do not grow well in the presence of UV-B if the visible light
and no transmittance below 290 nm) to remove all radiation
level is low (29). Therefore, a preliminary assessment of
below a given wavelength. It is also important to use an IR
satisfactory growth of the test organism under a given visible/
filter(suchasawaterfilterorIRreflector)toremoveheat.This
UV-B light source should be performed.
source provides high fluence rates over relatively large areas
8.4 Simulated Solar Radiation—ThevisibleplusUV-Blight
(;200 cm in diameter).
source described in 8.3 provides only UV-B and visible light.
In many cases, it is desirable to have UV-Apresent as well to
9. Transmission Properties of Lamp Coverings and
betterreplicatethesolarspectrum.Forinstance,itislikelythat
Laboratory Vessels
the level of blue light and UV-Arelative to UV-B is important,
9.1 Various clear media can be used to cover lamps to alter
asthesespectralregionsactivatedeoxyribonucleicacid(DNA)
their spectral qualities. There are also many types of clear
repair via photolyase (30, 31).Also, the UV-A/blue light level
laboratory containers. One can thus remove specific spectral
is important in plants for synthesis of protective pigments like
regions or generate light from a single spectral region. One
carotenoids. Thus, full spectrum artificial lighting, even at
caution that should be taken with coverings and laboratory
relatively low fluence rates, might compensate for the need for
vessels is that transmittance properties vary with thickness
high fluence rate visible light, as mentioned in 8.3. The
according to Beer’s Law. Therefore, if a 1mm thickness of a
visible:UV-A:UV-B ratio should be approximately 100:10:1 in
given material has 50% transmission at a certain wavelength,
a simulated solar radiation (SSR) source (18, 22). Unlike
then a 2mm thickness of the material will transmit only 25%
UV-B, the level of UV-A is relatively constant in the
at that wavelength.
environment, not varying greatly with latitude, altitude, or
season. Also, UV-A will not increase as the ozone layer is 9.2 Lamp Coverings:
depleted. In general, the IR can be left out of the light source 9.2.1 Removal of Ultraviolet—UVradiationcanberemoved
since it does not activate many biological processes and it with a variety of plastics or window glass. Cellulose acetate
E1733 − 22
film and polystyrene have cutoffs at 290 nm, therefore absorb- of the container needs to be made with a different material,
ing all of the UV-C. To prevent damage to the test organism, such as cellulose acetate, which transmits UV.
theUV-CusuallyneedstobequantitativelyremovedfromUV 9.3.4 Other Materials/Vessel Covers—Other types of con-
emittinglamps.Polyesterbasedclearplasticandmosttypesof tainerscanbeused,buttheymustbetransparenttothespectral
window glass have cutoffs between 330 nm and 380 nm and regionsimportanttothetest.Thetransmissionpropertiesofthe
materialcanbecheckedreliablywithaspectrophotometer.The
therefore can be used to remove UV-B and UV-C from a light
spectral quality of the light source can then be adjusted to
source. Plastic filters will degrade over time in UV, and they
compensateforabsorbancebythevessel.Itisalsoimportantto
should therefore be checked periodically with a spectropho-
consider any covers used on vessels in testing, and the amount
tometer to be certain that they have maintained satisfactory
and type of light they may block from reaching the organisms
spectral quality (usually less than 10% change in any spectral
in the test vessels.
region) (24).
9.2.2 Isolation of Spectral Regions—Except for specialized
10. Measurement of Light
tests, monochromatic or partially monochromatic light is not
necessary for environmental work. Broad band regions of the
10.1 LightComponents—Therearetwocomponentstomea-
visible spectrum can be isolated with colored theatrical grade suring light: quantity and quality (12, 13). Both are important
celluloids (spectral band widths approximately 50 nm to 100
aspects of a light source. When light is a concern, the quantity
nm). If narrower bandwidths are needed, interference filters of light must be measured each time a laboratory test is
performed. It is analogous to checking the pH of a solution.
can be used (5 nm to 20nm bandwidths); however, interfer-
ence filters will greatly limit the total fluence reaching the test Sincethespectraldistributionofalampisoftenavailablefrom
the manufacturer, the spectral quality does not require routine
organism. For more information on isolating specific spectral
regions, see Refs (12, 13). measurement. However, if different types of lamps are com-
bined into a single light source, the spectral output of the
9.3 Laboratory Vessels and Covers:
assembled radiation source should be measured with a spec-
9.3.1 Borosilicate Glass—Borosilicate glass is the most
troradiometer (see 10.3).
commonformofglassware.Itisusedtoholdorganismsduring
10.2 Measurement of Light Quantity—Lightquantitycanbe
toxicity tests. In particular, it is used for algae and L. gibba
measured in three ways: radiometric, quantum, and photomet-
growth because it is transparent to the visible light needed for
ric methods (12). In essence, each method uses the same type
photosynthesis. It is appropriate for many needs at thicknesses
of instrumentation, a light-sensitive detector (thermopile or
found in common flasks and petri plates (wavelength cutoff at
photodiode)thatconvertsanabsorbedphotonintoavoltageor
275 nm and 50% transmission at 295 nm). It therefore can be
a current and an amplifier to detect the voltage or current
used for any test in which UV-B is required. Of course, if
change (for other light measurement techniques see Refs (12)
wavelengths around 295 nm are needed, the investigator needs
and (13)). The amount of radiant energy should be reported as
to be sure that the amount of incident 295nm radiation is high
a fluence rate, although total fluence is appropriate under
enough to account for absorbance by the borosilicate glass.
certain circumstances. The biological test method being fol-
Also, very thick glass and low-grade borosilicate glass will
lowed should be consulted to determine the most appropriate
absorb UV-B. The transmittance properties of the material to
location to measure the light intensity. This may be the water
beusedshouldthereforebecheckedwithaspectrophotometer.
surface if the vessels are held in a water bath, at the surface of
9.3.2 Polystyrene—Polystyrene is the plastic generally used
the test vessels, or at the level of the test solution It may be
in petri dishes, culture bottles, and multi-well dishes. It has
desirable to measure the light intensity in several locations to
verygoodtransmissionproperties(commonthicknesseshavea
ensure all test vessels are within the required light range
cutoff at 288 nm and 50% transmission at 300 nm). It is
specified by the test method, as light intensity can vary along
thereforeusefulwithalmostanyenvironmentallyrelevantlight
the length of the light source (32, 33). It should be noted that
source. It also offers the advantage of absorbing all of the
LED lights may be brighter than other typically used light
incident UV-C. The only precaution that needs to be taken is
sources, and additional care may be required to ensure the
that all light measurements should be made with polystyrene
desired light intensity is achieved.
over the light sensor to account for any radiation absorbed by
10.2.1 Radiometric Methods—This is a measure of light
the plastic because this varies with the thickness of the plastic.
quantityinunitsofenergy(joules)orpower(watts).Therefore,
−2 −1 −2
Also,UV-CandUV-Bdegradetheplasticafterlongexposures
a fluence rate by this method will be J m s orWm . The
(approximately two weeks), so the plastic should be checked
instrument used is called a radiometer. The detector in a
periodicallyduringtestinganditshouldbediscardedaftereach
radiometer is a thermopile, which converts radiant energy to
test is complete.
heat and in turn generates an electromotive force. This results
9.3.3 Acrylic—Acrylic is used for many applications in inavoltagechangethatisproportionaltotheamountofenergy
environmentaltesting.Itisespeciallyusefulforbuildinglarger
absorbed.Thevoltagechangeisconvertedbyanamplifiertoa
−2 −1 −2
vessels for applications such as microcosm containment. Its calibrated output in J m s orWm . One can purchase
absorbance cutoff is around 385 nm, but this of course varies
radiometers with filters over the sensor that allow only certain
with the thickness of the plastic. For instance, 1cm thick spectral regions to pass. For instance, radiometers with filters
acrylic has 50% transmittance at 386 nm and 10% transmit-
that transmit only visible light are used by plant physiologists
tance at 379 nm.Therefore, if UVis needed in the test, the top because this is the photosynthetically active region (PAR) of
E1733 − 22
the spectrum; thus the name PAR meters. Also, one can buy
radiometers that have filter bundles that are specific for UV-A
or UV-B. These are used by meteorologists to make daily
UV-B readings that are now commonplace in weather reports.
One can also buy very accurate and sensitive radiometers that
detect over a very broad range (for example, from 200 nm to
2000nm)andcalibratetheradiometerforitssensitivityateach
wavelength.Thecalibrationiscrucialbecausethesensitivityof
all detectors is wavelength dependent.With appropriate filters,
the irradiance at a chosen wavelength can then be made.
10.2.2 Quantum Methods—This is a measure of light as the
number of photons present. Therefore, the result will be a
−2 −1
photonfluenceratewithunitsgenerallygivenasµmolm s .
−2 −1
(Note that this is equivalent to µEinstein m s ; see 3.2.2.)
The instrument used is called a quantum sensor. The sensor is
a light-sensitive diode (or photovoltaic cell), which converts
−2
NOTE1—ToconvertlxtoWm atagivenwavelength,dividelxbythe
absorbed photons to an electric current that is proportional to
numberontheyaxisatthewavelengthofinterest;thatis,ifalightsource
the number of photons absorbed. The amplifier then converts
had its primary output as red light centered at 600 nm, lx is converted to
−2 −1 −2
Wm by dividing by 420.
this information to a reading in µmol m s . However, the
−2
FIG. 11 Ratio of lx to W m as a Function of Wavelength
sensitivity of the sensor is wavelength dependent, so a filter
bundle is placed above the diode to quantum correct the
reading.Themostcommontypeofquantumsensorisbalanced
10.2.4 Conversion of Light Measurement Units—The
for visible light and, like the P
...