김경호
(Kyung-Ho Kim)
1iD
남현도
(Hyun-Do Nam)
2†iD
-
(Dept. of Electrical and Electronic Engineering, Dankook University, Korea)
-
(Dept. of Electrical & Electronic Engineering, Dankook University, Korea)
Copyright © The Korean Institute of Electrical Engineers(KIEE)
Key words
UV LED, UV lamp, Irradiation, Bactericidal test, Sterilization effect
1. Introduction
Generally a bacterium, microscopic single celled organism propagates itself well and
is known to inhabit in humid places[1]. Therefore, we live with commodities covered with invisible germs. There are various
sterilization and disinfection products on market to get rid of these germs. Commercially,
the majority of sterilizations are available by using UV lamps. The sterilization
by UV rays cause chemical changes to the nucleic acid component within the microorganism
and brings about metabolic disorder. For this reason, Sterilization is caused by proliferative
capacity loses[2]. UV rays mean electromagnetic waves in the range of 100-400 nm wavelength and divides
into UV-A, UV-B and UV-C[3]. UV-A is between 320-380 nm and the longest wave length in ultraviolet rays. UV-B
is the middle of ultra violet rays in between 280-320 nm. UV-C is the shortest wavelength
in between 180-220 nm[4].
UV LED is staying at the beginning stage of the market but seems possible to apply
with the sterilization (water, air), water purifier, deodorant, medical applications,
skin problem treatment identify counterfeit bills, light, textile and chemical industry,
environmental sensors, etc.[5]. In particular, small and environmental friendly products are on the trend[6]. The UV LED market seems to grow 30 million dollars every year, from 32.5 million
dollars in 2011 up to 150 million dollars in 2016. The use of UV LED is growing because
it is becoming high-powered and high efficient[7]. The UV LED market is expected to grow up to average 43% per year, with the existing
market to grow 10% over 5 years. The market share of UV LEDs are only up to 12.7%
and this point is expected to increase to 37.7% in 2017[7]. Most of UV LEDs are UV-A and UV-B wave length-products on market and UV-C is for
studies or science equipments. Many of sterilization products are known to use UV-C.
Sterilization by UV rays are different by depending on the type of microorganisms.
Near 260 nm wavelength, in other words, the wavelength for bactericidal effect is
best to absorb the nucleic acid[2]. But from the report[8], we can also know ultrasonic sterilizers, toothbrush sterilizers and water purifiers
use 380 - 410 nm wavelength with UV-A. And from the results of the E-coli death experiment
with 368.6 nm UV lamps, there was no significant change in the E-coli death rate for
30 minutes but eventually the death rate increased to 83.3% after 1 hour[9]. Many researchers have applied UV-C LEDs as a light source but the costs of the components
make it very difficult to apply UV-C LEDs to household goods[10-12]. This study is for development of sterilizers for small household goods and we study
and compare sterilization effects of UV LEDs(UV-A) and small UV lamps.
2. Materials and Method
2.1 Experiment method
UV LEDs are more expensive than UV lamps but if UV LEDs are adopted there are high
needs of sterilization and this has the advantage[8,9] of saving electricity consumption and extension of use. We choose UV LED of 380 nm
because 380 - 410 nm wave length including UV-A is used for sterilization besides
well known sterilization UV-C zone. We compared and measured reducing amount of bacteria
existing in purified water using UV LED with 380 nm and UV lamp as shown in Figure. 1 with 253.7 nm wavelength.
Fig. 1. UV LED and UV Lamp used in experime
At this time, undiluted purified water was left for 30 minutes to 1 hour. An experimental
container was specially made of 8 × 8 × 6 (Cm) stainless steel as Figure. 2 and a UV LED and UV lamp were placed at the upper part. To make the process simple,
we used 3M petrifilms for bacteria which were ready to incubate samples and culture.
The incubator made by Sam-woo scientific Co is used to culture bacteria for 48 hours
on 35 – 36℃.
Fig. 2. The experimental container used in the experiment
2.2 Bactericidal test
The experiment was divided into 3 cases. The purpose of this experiment is comparison
of sterilization using 380 nm UV LED and 253.7 nm UV lamp. In addition, based on the
result, we chose the valid way for sterilization, measured sterilization results by
irradiation time to set the effective sterilization time.
2.3 Bactericidal test using 380 nm UV LED
As a sample, we use purified water for 30 minutes – 1 hour without any other treatment
and checked sterilization with 380 nm UV LED in the sample. With the experimental
time of 20 minutes, 1 ml of the sample was taken by a micropipette every 5 minutes
and vaccinated on petrifilm. At this time, the control group was standard and the
experimental group used the sample which hourly applied 380 nm UV LED. The UV ray
sterilization has relation with not only the wavelength but also its intensity and
irradiation time. In the range of 300-400 nm, rather than to sterilize the bacteria,
rehabilitation phenomenon occurs and the bacteria thrives. Based on these information,
the irradiation time of the sample has been setup to 30 minutes[4]. Inoculated petrifilm was cultured for 48 hours in a incubator and then figured out
the number of cells by counting bacteria. The experiments were conducted 5 times on
a clean bench to prevent contaminated air as much as possible.
2.4 Comparison experiment of bactericidal test using 380 nm UV LED and 253.7 nm UV
lamp for equivalent hours
As a sample, purified water without any other treatment was used and irradiated with
a 253.7 nm UV lamp. The experimental time was 20 minutes, 1 ml of the sample was taken
by a micropipette every 5 minutes and vaccinated on petrifilm. At this time, the control
group was standard and the experimental group was the sample irradiated with the 253.7
nm UV lamp by the time. Inoculated petrifilm was cultured for 48 hours in a incubator
and the figured out the number of cells by counting bacteria. The experiments were
conducted 4 times on a clean bench to block contaminated air from inflowing as much
as possible. We got the cell number of bacteria by 253.7 nm UV lamp irradiation experiment
and the result from the above experiments. The death rates of bacteria were compared
by UV LED and UV lamp by equivalent time.
2.5 The experiment for sterilization time of bacteria using 253.7 nm UV lamp
As a sample, purified water without any other treatment was used and irradiated it
with a 253.7 nm UV lamp. The experimental time was 10 minutes, 1 ml of the sample
was taken by a micropipette every minute and vaccinated on petrifilm. At this time,
the control group was standard and the experimental group was the sample irradiated
with the 253.7 nm UV lamp. Inoculated petrifilm was cultured for 48 hours in a incubator
and then figured out the number of cells by counting bacteria. The experiments were
conducted 18 times on a clean bench to prevent contaminated air from inflowing. The
observation time was set based on the result of the experiment that used the 380 nm
UV LED and 253.7 nm UV lamp comparisons.
3. Results and discussion
3.1 Comparison of bacteria death rate by experiments
The bacteria death rate was able to be checked by counting bacteria on petrifilm in
the bacteria killing experiment. We can notice the bacteria death section by calculating
the reduction ratio of the standard group and experimental group. Each experimental
result is as the following.
3.2 Bacteria death rate using 380 nm UV LED
Table 1 shows the result of the bacteria death ratio using 380 nm UV LED. The experimental
group by UV LEDs showed repetitive increase and reduction. The average of 4 experimental
values did not show big changes on the initial cell number 147 CFU/ml as Table 1. The 380 nm UV LED is little effective on killing bacteria with the result of the
experiment as shown in Figure. 3. It also shows the same result of product cultured for 48 hours, the same process
as Experiment 1.
Table 1. The bacteria number change and reduction ratio according to using 380 nm
UV LED
|
|
Exp. 1
|
Exp. 2
|
Exp. 3
|
Exp. 4
|
Average
|
Average reduction(%)
|
|
Std.
|
77
|
130
|
120
|
262
|
147
|
-
|
|
5 min.
|
100
|
137
|
159
|
216
|
153
|
- 4.0
|
|
10 min.
|
85
|
1080
|
163
|
245
|
150
|
- 2.0
|
|
15 min.
|
65
|
133
|
138
|
173
|
127
|
13.6
|
|
20 min.
|
80
|
125
|
110
|
147
|
116
|
21.0
|
Fig. 3. The changes in the number of bacteria by using 380 nm UV LED
3.3 The comparison of the bacteria death ratio using UV LED in equivalent observation
time
Table 2 is about the experimental result of the bacteria killing experiment using 380 nm
UV LED and 253.7 nm UV lamp. UV lamp means 4 times the experimental value with 253.7
nm UV lamp.
Table 2. The changes in the number of bacteria by using 380 nm UV LED and 253.7 nm
UV lamp in equivalent observation time
|
|
UV LED
|
UV lamp
|
|
Experiment 1
|
Experiment 2
|
Experiment 3
|
Experiment 4
|
|
Standard
|
77
|
110
|
159
|
227
|
276
|
|
5 minute
|
100
|
15
|
3
|
3
|
5
|
|
10 minute
|
85
|
0
|
1
|
1
|
3
|
|
15 minute
|
65
|
0
|
0
|
1
|
0
|
|
20 minute
|
80
|
0
|
0
|
0
|
0
|
Figure. 4 is the graph for the number change of cells in the same observation time. The number
of cells did not change much with 380 nm UV LED but in the case of 253.7 nm UV lamp
decreased notably. All bacteria died 20 minutes later. In this experiment, 380 nm
UV LED and 253.7 nm UV lamp, the well known effective sterilization wavelength, were
compared. UV LED is little effective but the UV lamp is much more effective on sterilization.
Fig. 4. The changes in the number of bacteria by using 380 nm UV LED and 253.7 nm
UV lamp in equivalent observation time
On sides, we made sure that the UV lamp worked after 5 minutes. Also we can get the
same results from the bacteria cells cultured for 48 hours in the above Experiment
1.
3.4 Sterilization time and sterilization ratio with 235.7 nm UV lamp
We can make sure that the number of cells sharply decreases at 5 minutes and rarely
survived after 10 minutes. The average results of 18 tests shows the initial cell
number is 227 CFU/ml but over time it is tend to diminish as shown in Table 3 and Figure. 5.
Table 3. The bacteria number change and reduction ratio according to using 253.7 nm
UV lamp
|
|
Experiment 1
|
Experiment 2
|
Experiment 3
|
Experiment 4
|
Experiment 5
|
Experiment 6
|
Experiment 7
|
Experiment 8
|
Experiment 9
|
Experiment 10
|
|
Standard
|
201
|
163
|
370
|
113
|
544
|
604
|
64
|
71
|
324
|
73
|
|
1 Minute
|
137
|
71
|
254
|
100
|
457
|
429
|
42
|
41
|
236
|
55
|
|
2 Minute
|
85
|
43
|
214
|
55
|
340
|
386
|
16
|
6
|
246
|
23
|
|
3 Minute
|
37
|
16
|
97
|
37
|
235
|
255
|
3
|
1
|
112
|
14
|
|
4 Minute
|
27
|
15
|
47
|
30
|
177
|
87
|
2
|
1
|
36
|
4
|
|
5 Minute
|
15
|
7
|
15
|
28
|
105
|
18
|
1
|
1
|
20
|
2
|
|
6 Minute
|
7
|
3
|
9
|
19
|
54
|
15
|
1
|
1
|
14
|
2
|
|
7 Minute
|
4
|
3
|
5
|
8
|
45
|
9
|
1
|
0
|
7
|
1
|
|
8 Minute
|
0
|
2
|
2
|
6
|
25
|
2
|
1
|
0
|
3
|
1
|
|
9 Minute
|
0
|
1
|
1
|
5
|
18
|
1
|
0
|
0
|
1
|
1
|
|
10 Minute
|
0
|
1
|
1
|
5
|
7
|
1
|
0
|
0
|
1
|
0
|
|
|
|
|
Experiment 11
|
Experiment 12
|
Experiment 13
|
Experiment 14
|
Experiment 15
|
Experiment 16
|
Experiment 17
|
Experiment 18
|
Average
|
Average reduction (%)
|
|
Standard
|
154
|
202
|
185
|
54
|
184
|
299
|
303
|
172
|
227
|
-
|
|
1 Minute
|
129
|
108
|
97
|
40
|
126
|
212
|
193
|
144
|
160
|
29.5
|
|
2 Minute
|
45
|
96
|
18
|
22
|
122
|
147
|
128
|
95
|
116
|
48.8
|
|
3 Minute
|
16
|
12
|
9
|
15
|
69
|
139
|
82
|
50
|
67
|
70.4
|
|
4 Minute
|
7
|
5
|
3
|
9
|
55
|
66
|
46
|
12
|
35
|
84.5
|
|
5 Minute
|
7
|
5
|
1
|
2
|
27
|
33
|
32
|
11
|
18
|
92.0
|
|
6 Minute
|
5
|
4
|
1
|
1
|
6
|
11
|
12
|
9
|
10
|
95.5
|
|
7 Minute
|
3
|
3
|
0
|
1
|
5
|
9
|
5
|
6
|
6
|
97.3
|
|
8 Minute
|
1
|
2
|
0
|
1
|
4
|
8
|
4
|
3
|
4
|
98.2
|
|
9 Minute
|
1
|
1
|
0
|
0
|
3
|
6
|
3
|
1
|
2
|
99.1
|
|
10 Minute
|
1
|
1
|
0
|
0
|
1
|
3
|
2
|
1
|
1
|
99.5
|
Fig. 5. The changes in the number of bacteria by using 253.7 nm UV lamp
Specifically it is decreased more than 90% after 5 minutes and 99.5%, bactericidal
effect, after 10 minutes.
4. Conclusion
In this research, we studied the effect of sterilization by UV LED and UV lamp. We
had applied 380 nm UV LED because 380–410 nm wavelength of UV LED was used for sterilization
in general and also had applied 253.7 nm UV lamp based on the report that used 368.6
nm wavelength UV lamps on E-coli tests.
The result shows 380 nm UV LED did not give a great impact on killing bacteria when
we observed it in samples for 20 minutes. Also 380 nm UV LED and 253.7 nm UV lamp
comparison experiment showed that UV LED is not significant on sterilization but UV
lamp was effective on killing almost every cell after 10 minutes. For 4 minutes of
observation, 253.7 nm UV lamp made the number of cells decrease quickly and showed
90% of reduction after 5 minutes and 99.5% sterilization effect after 10 minutes.
From the further study, we will apply this result to personal sterilizers for health.
Acknowledgements
이 논문은 의하여 연구되었음.
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저자소개
1996: 일본 게이오대학 공학석사
1999: 일본 게이오대학 공학박사
2006~현재: 단국대학교 전자전기공학부 교수
1981: 서울대학교 공학석사
1986: 서울대학교 공학박사
1982~현재: 단국대학교 전자전기공학부 교수