Creative Education
2012. Vol.3, No.4, 600-602
Published Online August 2012 in SciRes (http://www.SciRP.org/journal/ce) http://dx.doi.org/10.4236/ce.2012.34088
Copyright © 2012 SciRe s .
600
Teaching an Environmental Chemistry Experiment—A
Case Study
——Simple Test for Measuring the Emission Spectra of Lamps
Lin Zhang, Long Chen, Mei Xiao, Feng Wu*, Nansheng Deng
Department of Environmental Science, School of Resources and Environmental Science,
Wuhan University, W u h an , China
Received May 24th 2012; revised June 30th, 2012; accepted July 10th, 2012
Here we present the significance, content, results, and teaching effect of a selective self-design experi-
ment—a simple test for measuring the emission spectra of artificial light sources, and discuss its function
and potential problems in an environmental chemistry class for undergraduate students. Also, we propose
several ways to reform experimental teaching, and provide references to other experimental courses.
Keywords: Self-Design Experiment; Spectrophotometer; Spectrum; High Pressure Mercury Lamp;
Deuterium Lamp
Introduction
Laboratory courses are a crucial component of a National
Quality Course (NQC)—Environmental Chemistry. In this re-
search group, we believe that the construction and reform of
this subject is important, and our core task is to develop teach-
ing quality, improve students’ experimental abilities, promote
motivation and enthusiasm, inspire a spirit of scientific explora-
tion and creativity, thus enabling students to conduct scientific
research and solve practical problems.
The aim of the NQC is to settle various problems regarding
the construction of course content, and we as NQC instructors
manage and design the laboratory teaching ourselves, and in-
creasingly self-design comprehensive experiments. We offer
opportunities for students to gain knowledge, develop their re-
search abilities, and enhance their independence. Meanwhile,
we reform the laboratory teaching methods, and encourage dis-
cussion and an active class atmosphere, to inspire students’
brainstorming abilities, and to enhance the teaching effect.
In the following case—a simple test for a lamp emission
spectrum, we briefly illustrate how students’ research abilities
are clearly improved through designing an experiment.
Objective of This Study
Ultraviolet and visible (UV-Vis) spectrophotometry is one of
the most practical and functional tools in quantitative analysis,
and a UV-Vis spectrophotometer (UVVS) is one of the most
commonly used instruments in laboratory teaching for envi-
ronmental major undergraduates. Therefore, most instructors
will regard this as critical. While in laboratory class, the pur-
pose of setting up this experiment is to: make students learn
about the inner structure and working principle of a UVVS
through disassembling it, e.g. the characteristics of emission
spectra of a high pressure mercury lamp (HPML) and deute-
rium lamp (DL) using remolded UVVS; increase their theoreti-
cal knowledge about optics via determining emission spectra of
several artificial light sources; promote their comprehensive
scientific research ability and the ability to design experiments
by composing an experimental plan, accomplishing it and sub-
mitting the final result in the form of an essay.
Experimental Principle
The UVVS consists of four major parts: a light source, a
beam splitting system, an absorption cell, and a detection sys-
tem (Figure 1). In order to determine the illumination intensity
of our target lamps (HPML and DL), in different wavelengths,
we need to utilize the beam splitting system to split the con-
tinuous spectra, thus fully taking advantage of regular UVVS.
Therefore, we only have to alter the light source for other
sources to be examined, and after adjusting the wavelength we
can obtain the transmissivity (T) for different wavelengths.
In this experiment, we need a baseline to quantify the relative
emission intensity. Therefore, the value of T for a specific
wavelength has to be fixed to 0%, in which there might be lu-
minance. The relative intensity in other wavelengths can be
quantified by subsequent comparison. Similarly, we can also
fix the value of T of a specific wavelength to 100%, and then
perform the same process described above. Given the fact that
there is a glass cover on the mercury lamp and there is no
transmission in wavelengths less than 280 nm, 280 nm was
chosen as the baseline and fixed to 0%, and we determined the
spectra up to 800 nm. However, for the DL, the cover is made
of quartz, thus having lower absorption limit (160 nm). There-
fore we should set 160 nm as the baseline, but because the
shortest wavelength we can use in the UVVS is 180 nm, we set
180 nm as the baseline, and also continued up to 800 nm.
Owing to the limits of the laboratory, we could not evacuate
the absorption cell. However, in fact, the impact of air is negli-
gible.
*Corresponding author.

L. ZHANG ET AL.
Figure 1.
Inner structure of a UVVS.
Instruments
Instruments included the UV-9100 UVVS, an HPML, an
iron support, a screwdriver, nipper pliers and a wrench. The DL
used was in the UVVS itself.
Experimental Method
Study of the DL Emission Spectrum
Before determination, the UVVS was switched on and the
DL was preheated for 15 min. Then we put the lid on, adjusted
the wavelength to 180 nm, and made T = 0%. The wavelength
interval was preliminarily set at 10 nm, but when it approached
the peak, 2 nm was more appropriate. Because the UV-9100
UVVS cannot achieve more accurate performance, and larger
intervals cannot precisely portray the spectrum. The wavelength
was altered and T was recorded until 800 nm was reached. Af-
ter the experiment was completed, both the DL and UVVS
were switched off, and the power cable was unplugged.
Study of the HPML Emission Spectrum
For the sake of safety, the power cable was unplugged. To
eliminate the effect of DL and the tungsten lamp, they had to be
removed before the experiment. The outer cover was lifted, and
the top lid on the lamp house was removed. Then the three
wires connected to the DL were screwed off, clamped by the
nipper pliers, then the tightened screws were unscrewed using a
screwdriver. Then the DL could be extracted from UVVS. The
tungsten lamp was removed using the same method. Then the
outer cover was replaced, and the dam-board in front of the
light sources was removed. With the iron support, the HPML
was fixed opposite the optical channel. Then the position of
HPML was adjusted to focus its radiation on the optical col-
lector. After 15 min preheating the HPML, the UVVS was
switched on. For this experiment, 250 nm was selected as the
baseline, and 2 nm was chosen as the wavelength interval until
800 nm was reached. After the experiment the UVVS was re-
stored, and the HPML was removed.
Results
The data are presented respectively for the emission spectra
of the HPML and DL. To analyze their accuracy, they were
compared with standard emission spectra (Emission Spectra of
mercury light, deuterium light and tungsten lamp. Available
online) in detail. All the spectra are presented in Fi gures 2 and 3.
Discussion
Coincidence Analysis between Standard and
Experimental Spectra
By comparison with standard spectra, we found the experi-
mental spectra of both HPML and DL coincided with them
significantly. In particular, the emission peaks of HPML at 404
nm, 436 nm, 546 nm and 577 - 579 nm were all delineated.
Moreover, the main peak at 365 nm was accurately depicted.
However, the standard spectrum of the DL is far more complex
than that of the HPML, since the spectral bandwidth of its slit is
comparatively tiny, and can scan adjacent wavelengths. There-
fore, to clearly demonstrate the distinction, this standard spec-
trum was fitted to a modified and smooth curve, in which the
peaks were in good agreement with the experimental spectrum,
as shown.
Difference Analysis between HPML and DL Emission
Spectra
Obvious differences in emission spectra can be observed
200 300 400 500 600 700 800
0
2
4
6
8
10
12
14
16
T
wavelength λ(nm)
Experimental Spectrum
Standard Spectrum
Figure 2.
Emission spectra of DL.
300 400 500600 700 800
0
5
10
15
T
wavelength λ(nm)
Experimental Spectrum
Standard Spectrum
Figure 3.
Emission spectra of HPML.
Copyright © 2012 SciRe s . 601

L. ZHANG ET AL.
Copyright © 2012 SciRe s . 602
between the HPML and DL—the spectrum of the former is
scattered, while the spectrum of the latter is more continuous.
This is because the irradiation of the mercury lamp depends on
atoms. After they absorb energy from the high voltage, the
electrons can move to higher energy levels, and this process is
called transition. Because higher energy levels result in unsta-
ble states, some electrons will return to lower energy levels,
releasing electromagnetic radiation. Moreover, with increasing
mercury vapor pressure, the atomic collision becomes more
frequent and intense, so the emission spectra will be more and
more continuous. In fact, the emission spectrum of an ultra high
pressure mercury lamp is almost band spectrum. However, a
DL can radiate a continuous spectrum in the ultraviolet band.
That is why the DL can be the ultraviolet light source for a
UVVS.
Effect Analysis of This Experimental Method
With the widespread use of various lamps and developments
in lamp technology, nowadays the life span, energy saving
performance, light color etc. are greatly improved. Sometimes,
the absolute calibration of the spectral irradiance, especially in
modern research, is necessary. Tang et al. (Tang & Li, 1996)
has studied the absolute calibration in short wave areas of the
DL. Huang et al. (Huang, Wang, Zhang, Lin, & Li, 2007) once
used a DL to standardize the irradiance in wavelengths between
200 and 300 nm, while Wang et al. (Wang & Zhu, 1992) dis-
cussed methods to automatically collect mercury lamp spectra.
Although very precise, these methods are very costly, and un-
necessary for undergraduate students. However, in this experi-
ment, we determined the spectra by comparison with the base-
line, and obtained relatively accurate and practical emission
spectra for the HPML and DL. Therefore, using this original
and cheap method, undergraduate students obtained a good
command of the characteristics of emission spectra of several
artificial light sources, and how to explore scientifically and
practically.
Conclusion
This self-design experiment system fully takes advantage of
a UVVS in the laboratory setting, utilizing its basic principle to
determine t he emission spe ctra of a HPML and DL. The results
fit very well with standard spectra. The reason for lack of de-
tailed spectral characteristics of DL is because the spectral
bandwidth is too large to achieve a more detailed determination.
Compared with absolution calibration, which is prevalent now-
adays, this method is quite simple and inexpensive. In addition,
it can enhance students’ understanding of UVVS, as well as the
emission spectra of lamps discussed above.
Implications of the Study
This entire process is a self-design experiment. Initially, stu-
dents were requested to consult the literatures through the li-
brary or Internet resources, and put forward a plan after group
discussions which included 10 - 12 members. Then the instruc-
tor organized all the students to participate in the discussion,
and each group was required to state their plan, and to reply to
various questions raised by the other students. Before the ex-
periment, the plan was recomposed accordingly. In addition, an
essay was require d for submi ssion after the experiment.
This is the 5th year of this self-design experiment series. We
aimed to perfect these self-design experiments so that students
can display their creativity, actively participate and boost mo-
rale, enjoy the sense of success, and share their skills with oth-
ers. However, some problems were inevitable. First, laboratory
instruments, reagents and funds are limited, and sometimes
cannot fulfill the students’ ideas. Second, due to the lack of
laboratory class hours, we could not conduct some time-con-
suming and complicated experiments, which may have facili-
tated their subsequent studies. According to this experience, we
will re-schedule class time distribution for basic, comprehend-
sive and self-design experiments, leaving more time for the
self-design series. Beyond that, more channels for funds, in-
struments and reagents will be definitely explored.
In conclusion, time has shown the benefits of self-design ex-
periments. Not only can the students attain increased creativity
and comprehensive knowledge, but also attain a solid founda-
tion for their future success.
REFERENCES
Emission spectra of mercury light, deuterium light and tungsten lamp.
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Huang, Y., Wang, S. R., Zhang, Z. D., Lin, G. Y., & Li, F. T. (2007).
Calibration of 200 - 300 nm spectral irradiance using 150 W deute-
rium lamp. Optics and Precision Engineering, 15, 1215-1219.
Tang, Y. G., & Li, F. T. (1996). Absolute calibration of the spectral
irradiance of quartz window deuterium lamp in 200 - 350 nm. Spec-
troscopy and Spectral An a l ys i s , 16, 7-10.
Wang, Q., & Zhu, Z. Q. (1992). Automatic collecting method of mer-
cury lamp spectrum. Opto-Electronic Engineerin g, 19, 52-56.