No.10 Ecological issues and Nemoto's approach - (1) "Glow-starters for Fluorescent Lamps" (June 15,2001)

Written by; Y. Murayama
Technical Advisor
Nemoto & Co., Ltd., Tokyo

In the article "Fluorescent Lamps and Nemoto" that I wrote in '99, I explained that the special type of lead-in-wires that Nemoto developed were used in the glow-starters for fluorescent lamps. This special electrode wire, which contains a very small amount of radioactive material, helped to make lamps ignite faster after switching them on.

To satisfy the increasing demand for this special electrode wire, Nemoto manufactured over 3 billion pieces of these special lead-in-wires for fluorescent lamps during the period from 1974 to 2000.

As it has become inevitable for many businesses to take responsibility for the environment, many companies have implemented environmentally friendly policies.
Under such circumstances, it was expected that the glow-starters would draw harsh criticism in the market because of the radioactive materials that can damage the natural environment even if the radioactivity they contained was just a minute amount and safe.

In anticipation of such circumstances, Nemoto's R&D sought a way to improve discharge starting characteristics of glow-starters without using radioactive materials. One of the possibilities was utilization of LumiNovaR that Nemoto & Co., Ltd. had invented in 1993.
As a result of research achievements, we made a presentation in June 1997 of the results we received at "The 12th Workshop of Illuminant Physicality and Application" that was jointly hosted by IEIJ (Illuminating Engineering Institute of Japan) and JSAP (Japan Society of Applied Physics).

The mechanism of the afterglow from phosphorescent pigment that improves the discharge starting characteristics of glow-starters in a dark place is different from conventional ones that utilize radiation ionization.
This innovative idea is to stimulate barium oxide (emitter) at the surface of the glow-starter's electrode with afterglow from phosphorescent pigments. This photoelectric effect encourages electron emission from the emitter with a loss of electrons, which in turn activates discharging.

For the experiments, the following three kinds of long afterglow phosphorescent pigments were used.

Chemical composition	Emission color	Emission peak wavelength
SrAl₂O₄:Eu,Dy (G)	Yellowish Green	520nm
Sr₄Al₁₄O₂₅:Eu,Dy (BG)	Bulish Green	490nm
CaAl₂O₄:Eu,Nd (V)	Violet	440nm

Picture: Glow-starter equipped with phosphorescent pigments
(circular part at the top is phosphorescent pigments)

As shown in the photograph, experiments were done as follows:
1. Glow-starters without radioactive material were equipped with phosphorescent pigments
2. Glow-starters were excited for 30 minutes with the equivalent luminance (10,000 lux) that is available where glow-starters are usually placed
3. After the above excitation, glow-starters were placed in a dark place and relations between elapsed time and discharge starting time were measured

Fig.1: Types of phosphorescent pigments and discharge starting properties

The result of these experiments shows that all three types of phosphorescent pigments are effective for the purpose. Among them, however, it is found that the higher the photon energy (the shorter the emission wavelength), the better the discharge starting characteristics. It means that LumiNovaRV (CaAl2O4:Eu,Nd) is the most advantageous material to be used for this purpose.

Fig.2: Time after excitation (in dark place) and discharge starting properties

And it is confirmed that the glow-starter with only 40mg of LumiNovaRV (CaAl2O4:Eu,Nd) shows almost equal characteristics to the conventional radioactive type lamps even when they are placed 168 hours ( 7 days) in a dark place.

This outcome shows that the glow-starters with phosphorescent pigments are by no means inferior when used in locations where natural light is available during daytime and in basements or dark rooms even if it is lighted only once in a week.

At the moment, evaluations and further trials are being done internationally for this application and it is expected products based on this finding will soon be commercially available.

Nemoto is very proud that its LumiNovaR product contributes to conservation of nature in this product area as it did in the watch and clock industry.

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