A Review on artificial lighting of tissue cultures and transplants

A REVIEW ON ARTIFICIAL LIGHTING OF TISSUE CULTURES AND TRANSPLANTS

Wei Fang and R.C. Jao

Dept. of Agricultural Machinery Engineering

National Taiwan University

136 Chou-Shan Rd., Taipei, Taiwan

Email: weifang@ccms.ntu.edu.tw

Abstract

Tubular fluorescent lamps (TFLs) are principally used in multiple-layer tissue cultures (TC) and transplants production. HF electronic fluorescent lighting system with light regulation provides not only energy saving but also the capability of adapting the quantity of light to the stages in the development of the TC plants. Direction, uniformity, quality of light and various efficient light sources were studied worldwide. Super bright red, blue and far-red light-emitting diodes (LEDs) have many advantages over conventional light source for photosynthesis and morphology research. The characteristics of such LEDs were reviewed. Simulation models of spatial distribution of intensity, conversion factors among photometric, radiometric, and quantum units, and the electrical energy efficiency of TFLs and LEDs were discussed. The cost effectiveness of using LEDs in commercial TC and transplants production was discussed. A growth chamber using LEDs as light source, capable of adjusting light quantity and quality, can be a great tool for research and the development of such a system can be cost effective.

Keywords: Artificial lighting, Supplemental lighting, Light-emitting diodes, LEDs

本文發表於 International Symposium on Transplant Production in Closed System for Solving the Global Issues on Environmental Conservation, Food, Resources and Energy. Chiba, Japan. 28 February - 2 March, 2000.

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1. Introduction

Various types of light source can be used in horticulture including incandescent bulb, tubular fluorescent, compact gas-discharge, high-pressure mercury, metal halide and high-pressure sodium lamps. Incandescent bulb is popular in photoperiodism control and compact gas-discharge lamps are normally used for decorative and display purposes. Besides these two types, others can be used for photosynthesis (Philips lighting, 1992). Tubular fluorescent lamps (TFLs) are principally used in multiple-layer tissue cultures (TC) and transplants production (Ikeda et al., 1992; Fang and Jao, 1996). HF electronic fluorescent lighting system with light regulation provides not only energy saving but also the capability of adapting the quantity of light to the stages in the development of the TC plants. The radiant efficiency (mW/W) and luminous efficacy (lm/W) of various light sources are listed in Table 1.

Table 1. Radiant efficiency (mW/W) and luminous efficacy (lm/W)of various light source used in horticulture

Lamp type	Radiant efficiency (mW/W)*	Luminous efficacy (lm/W)
Incandescent	62	14.8
Fluorescent	220-270	64-93
Compact gas-discharge	138-170	50-67
High-pressure mercury	124-166	40-57
Metal halide	227	78
High-pressure sodium	313-316	125-137

* Values adapted from Philips lighting (1992)

Energy cost is one of the major concerns for commercial applications when using artificial lights. Various efficient light sources were investigated worldwide. A microwave-powered lamp, developed by an American company (MacLennan et al., 1995), has many advantages over conventional lamps for use in artificial lighting of plants (Kozai et al., 1995; Kozai and Kubota, 1997).

Recent developments have resulted in greatly increased light output for red and blue light-emitting diodes (LEDs). LEDs with the characteristics of high energy-conversion efficiency and low thermal energy production, thus, making it a promising light source for plant growth in confined environment (Bula et al., 1991; Hoenecke et al., 1992).

The objectives of this study were to review the means in applying tubular fluorescent lamps and investigate on the promising new light source - LEDs.

2. Lighting cycle, direction and quality of light

2.1. Lighting cycle

Morini et al. (1990) reported that the shorter lighting cycle promote the plant growth. Hayashi et al. (1993) examined the effects of the 24-, 6-, 1.5-, and 0.375-hour lighting cycles on growth of potato plantlets cultured photoautotrophically. The ratio of light/dark period is kept at 2:1 in all treatments. The result was consistent with Morini's conclusion. A continuing research of Hayashi et al (1995) found that shorter lighting cycles resulted in a higher average CO₂ concentration during the photoperiod and a higher CO₂ exchange rate, thus, promoting the growth of plantlets.

2.2. Lighting direction

Traditionally, artificial light was provided from the top of plants. Hayashi et al (1992) examined the lighting from the side of plantlets using TFL and showed a number of advantages including a reduction of shoot length, an increase in dry weight and a more efficient use of culture space. Kozai et al. (1995) used diffusive optical fibers to provide sideward lighting in a growth chamber. High quality transplants with short and thick stems can be obtained. Fang and Jao (1996) developed a movable TFL-mounting fixture attached to a multi-layer TC bench and investigated on downward, sideward and downward plus sideward lighting. The result showed that the movable downward lighting provide the most uniform distribution of light on bench. Advantages of using such a TFL-mounting fixture in addition to the uniform distribution of light including efficient use of space (lamp to plant distance can be reduced), less electricity cost and less number of lamps required.

2.3. Light quality

Light quantity and spectral quality have effects on plants in both photosynthesis and photomorphogenesis. Tubular fluorescence lamp (TFL) was the most popular artificial light source in tissue culture and growth room. Various types of TFL with different spectral quality were commercially available. Thimijan and Heins (1983) conducted a thorough investigation on the conversion factors among photometric, radiometric and quantum units of various types of artificial light. Among which, 4 types of TFL was included. Fang and Jao (1996) added 18 more commercially available TFL to the list of conversion factors.

Specially designed light source with different light quality were also under investigation. Sase and Ling (1996) used HID lamps providing white, blue, green and yellow light to investigate the growth of lettuce. Bula et al. (1991) showed that growing lettuce with red LEDs in combination with blue TFL is possible. Hoenecke et al. (1992) verified the necessity of blue photons for lettuce seedlings production using red LEDs with blue TFL. Super bright blue LED was not available until 1993. Nichia chemical industries of Japan succeeded in producing high intensity blue LEDs. Since then, companies such as Hewlett Packard of U.S., Panasonic, Toshiba of Japan and Everlight, Excellence of Taiwan started to produced super bright blue LEDs.

Yanagi et al. (1996) used super bright blue and red LEDs as the light source to investigate the effects of the quality and quantity of light to the growth and morphogensis of lettuce. Okamoto et al. (1996) used super bright blue and red LEDs as the light source to develop LED PACK, BIOLED, UNIPACK, and COMPACK with respect to their structure, function, circuit design and characteristics.

By changing the photon flux ratio in red(R, 600-700nm)/far red(FR, 700-800nm) radiation of artificial lights or daylight, the stem elongation can be controlled. R/FR and Blue(B, 400-500nm)/R ratios of 18 types of TFL and the combination of each TFL out of 18 types with red TFL or Agro-lite (Philips Lighting) were investigated (Fang and Jao, 1996). Schuerger et al. (1997) showed that the effects of spectral quality on anatomical changes in stem and leaf tissues of peppers were correlated to the amount of blue light present in the primary light source. R/FR and B/R ratios of sunlight transmitted through various colored solid and liquid transparent filters were also investigated (Fang et al., 1999).

3. Light-Emitting Diodes

3.1 Characteristics

Super bright red, blue and far-red LEDs have many advantages over conventional light source for photosynthesis and morphology research (Bula et al, 1991; Miyashita et al., 1995). The characteristics of such LEDs available locally were measured and compared with the data sheet provided by the manufacturers. Table 2 shows 3 types of super bright red LEDs and 4 types of super bright blue LEDs. Table 3 shows the conversion factors between quantum and photometric units of super bright LEDs. Characteristics of LEDs used in the literature were also compiled as listed in Table 4.

Table 2. Super bright red and blue LEDs measured in this study

Manufacturers	Model	mcd (no. of measured)	mcd from Data sheet	Peak wavelength
Everlight, Taiwan	383URC-3	2372 (5)	2000-3000	660 nm
Excellence, Taiwan	5ERBCCW-DG	8579 (30)	6617	622 nm
Hewlett Packard	HLMP-EG08-VY000	3757 (30)	3600-13800	626 nm
Nichia, Japan	NSPB500S	3533 (4)	3700	470 nm
Everlight, Taiwan	333-UBC	219 (14)	630-1000	430 nm
Excellence, Taiwan	5GBCCCT-EG	1631 (30)	2500	467 nm
Hewlett Packard	HLMP-CB16	1900 (30)	1575	472 nm

Table 3. Conversion factors of super bright LEDs measured in this study

Manufacturer (Color)	mcd^*1	mW^*2	Quantum^*3, μmole/m²/s	Photometric^*4 Lux	μmole/m²/s per lux	mW per μmole/m²/s
Hewlett Packard (Red)	3230	37	11.03	374.4	0.029	3.35
Excellence, Taiwan (Red)	5878	45.8	11.08	479.6	0.023	4.13
Everlight, Taiwan (Red)	2207	37	10.27	135.1	0.076	3.60
Hewlett Packard (Blue)	1899	64.2	10.41	195.3	0.053	6.2
Excellence, Taiwan (Blue)	1670	70.4	4.83	99.6	0.048	14.57
Everlight, Taiwan (Blue)	205.6	80	1.09	14.9	0.073	73.39
Nichia, Japan (Blue)	3460	68	6.27	188.3	0.033	10.84

*1. Measured using photometer (J17) with J1805 LED head (TekLumaColor, Inc.).

*2. Forward current at 20mA.

*3. Measured 10 cm away using LICOR 190SB quantum sensor.

*4. Measured 10 cm away using photometer (J17) with J1811 Luminance head (TekLumaColor, Inc.).

Table 4. The characteristics of LEDs listed in the literature.

Company (Model)	Peak wavelength	Power consumed (standard current)	quantum yield (Luminous Intensity)	Source
N/A	660 nm	N/A	N/A	Bula et al., 1991
Stanley Electric Co. Ltd. (H1000)	660 nm	40 mW	N/A	Miyashita et al., 1995
Stanley Electric Co. Ltd.	730 nm	N/A	N/A	Miyashita et al., 1995
Nichia (NLPB520)	450 nm	72 mW (20mA)	N/A	Okamodo et al., 1996
Toshiba (TLRA120)	660 nm	36 mW (20mA)	N/A	Okamodo et al., 1996
Shinko Denshi	730 nm	N/A	N/A	Okamodo et al., 1996
Panasonic (LNG992CF9)	N/A Blue	68 mW (20mA)	145 μmole/m2/s (1400 mcd)	Ono et al., 1997
Panasonic (LNG901CF9)	N/A Blue	N/A	(500 mcd)	Ono et al., 1997
Toshiba (TLSH180P)	623 nm	42 mW	180 μmole/m2/s (7000 mcd)	Ono et al., 1997
Panasonic (LN261CAL,UR)	665 nm	N/A	(2000 mcd)	Ono et al., 1997
Rohm (SLA570JT3)	660 nm	N/A	(1000 mcd)	Ono et al., 1997
Rohm (SLA570MT3)	660 nm	N/A	(1000 mcd)	Ono et al., 1997
Quantum Devices, Inc. (3009A001)	660 nm	N/A	N/A	Schuerger et al., 1997
Quantum Devices, Inc. (3009A002)	735 nm	N/A	N/A	Schuerger et al., 1997

3.2. Cost effectiveness

LEDs have been proposed as a primary light source for space-base plant research chamber or bioregenerative life support systems (Bula et al., 1991; Barta et al., 1992). At that time, it was not ready for commercial operation. Recently, the price of both blue and red LEDs have reduced and the brightness have increased a lot. The cost effectiveness of using LEDs in a commercial TC production is still in question. The UNIPACK (Okamoto et al., 1996) consists of a cultural vessel (11 cm x 11cm x 14 cm) and a light source named LEDCAP containing 9 blue LEDs and 36 red LEDs. The price for blue and red LEDs are 27 and 3.3 NT$ (Price in Taiwan at August of 1999), respectively. LEDs in LEDCAP will cost 361.8 NT$ (11.67 US$ with exchange rate 31:1) which is not acceptable to most of the TC plantlets producers.

4. Simulation

Simulation models of spatial distribution of intensity of TFLs and LEDs were developed (Fang and Jao,1996; Takita et al.,1996). TFL and LED are considered as line and point light source, respectively. The TFL model is flexible in defining the arrangement of TFLs on top of a bench and the LED model can display a perspective view of the PPF distribution and a contour map of the B/R ratio with fixed arrangement of blue and red LEDs. Both models were validated using measured spatial data.

5. Conclusion

Various types of artificial light source were available in horticulture. Tubular fluorescent lamp was the most popular and cost effective light source used for TC and transplants production and still is. Searching for efficient artificial light source and better means to apply the light is a continuing task. At present, using super bright LEDs as primary light source looks promising but not cost effective for the design such as LEDCAP in a commercial scale operation. A growth chamber using LEDs as light source, capable of adjusting light quantity and quality, can be a great research tool. Development of such systems can be cost effective.

Acknowledgment

The authors are thankful to Splendor Green Co., Ltd. of Taiwan for the support of funds.

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