WO2010128424A2

WO2010128424A2 - Fluorescent lamp

Info

Publication number: WO2010128424A2
Application number: PCT/IB2010/051826
Authority: WO
Inventors: Christianus J. Roozekrans; Pieter J. Stobbelaar; Geert C. M Van Hoof; Herman J. G. Gielen; Leendert H. Goud
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-05-04
Filing date: 2010-04-27
Publication date: 2010-11-11
Also published as: WO2010128424A3

Abstract

The invention is concerned with a fluorescent lamp having a lamp vessel. According to the invention the lamp vessel comprising a noble gas mixture of Xe and either Ar or Ne.

Description

Fluorescent lamp

The invention relates to an energy saving fluorescent lamp.

There are several types of energy saving (ECO) TLD lamps recently introduced in the market. In principle, the normal gas filling is replaced by a gas filling with a heavier atom weight (e.g. Xenon gas is added to the normal noble gas mixture). In this way the lamp voltage and the lamp power is reduced. The loss of light can be compensated by the application of an optimal phosphor coating.

The purpose of the invention is the provision of a lamp suitable to replace the known lamp in existing fixtures and arrangements and having a power saving over the known lamp of at least 5% without visible light losses.

It is known that by using a heavier filling gas, that is a gas filling with a heavier atom weight, discharge instabilities can occur. They occur mainly at lower than optimal mercury pressure, typically at ambient temperatures below 25°C. Due to the frequencies (5-20 Hz) of the discharge instabilities they can be annoying to the eye.

Investigations have learned that the intensity of the instabilities is depending on the amount of the gas filling, e.g. the Xe gas, the filling pressure and the composition of mixture of gasses of the gas filling. The instabilities decrease typically with increasing lamp power and wall load of the lamp. As this results in lower energy saving, this is not an option for energy saving (ECO) TLD lamps. However, it is found that the severity of instabilities of the discharge in the lamp can significantly be reduced depending on the type of gas that is added in the gasfilling to the Xe gas. More specifically, it is found that the use of the Ar/Xe gas combination as gas mixture leads to the lowest instabilities at a given lamp power. Lamps having mixtures with Kr/Xe or Kr/ Ar/Xe gasses show more discharge instabilities at the same power and comparable operating circumstances.

Figure 1 shows that the addition of Xe gas in a Kr gas lamp leads to unacceptable discharge instabilities (see A to B). In the other series, different mixtures of Xe/Rr/Ar are tested with different filling pressures. They can lead to relative high lamp power savings but at the same time to high levels of instabilities. It was surprisingly found that only the Xe/ Ar mixtures in all cases lead to stable operating lamps in combination with the targeted savings in lamp power of at least 5%, in many cases even about 10%, without any visible loss of light. Comparable results were achieved in lamps having a Xe/Ne mixture. This leads to the conclusion that for efficient energy saving TLD lamps a mixtures of Xe and a low atom weight rare gas Ar or Ne leads to a more stable discharge when compared to Xe and Kr or Kr Ar mixtures.

Preferably the gas mixture in the lamp should contain 30 to 70 vol.% Ar and 1.5 to 3 mbar filling pressure at 20 OC of the Ar and Xe together in order to realize system energy savings of about 10%.

For a rare gas mixture of Ne and Xe the Ne should be present in about 20 to 60 vol. % with a total filling pressure of 1.5 to 3 mbar.

In a prefered embodiment the lamp vessel wall is provided with phosphor layer of RGB (red, green and blue) phosphors known in the art having a mean particle size of about 6μm. Mean particle size is understood to mean the mean radius of the phosphor granules when considered spherical in shape. This results in an increase of lumen output with respect to the known lamp having a mean particle size of about 3μm. The lumen output increase is further promoted by increasing the applied mass of the phosphor layer from about 1.3 mg/cm2 to about 4.4 mg/cm2. In a preferred embodiment the lumen output has been increased with about 15% in comparison with the known lamp.

A further increase of mean particle size does not provide for further significant increase in uv-absorption. At the same time a further increase in phosphor layer mass, thus in further increase in layer thickness will result in loss of light output due to absorption and multiple refraction.

An embodiment according to the invention having a lamp vessel with identical dimensions as a prior art lamp of the type TLD Master 36 W/840, make Philips was operated at an air temperature of 25 to 30 degrees centigrade. The lamp vessel wall was provided with a layer comprising a red, a green and a blue phosphor also known as a RGB phosphor layer having a mass of 4.2 to 4.4 mg/cm2 and a mean particle size of 6 μm, resulting in a mean phosphor layer thickness of 17 to 18 μm. The RGB phosphor layer consist of 42 w % YOX (yttrium oxide) as red phosphor, 46 w % LAP (Lanthanum phosphate) as the green phosphor and 12 w % SECA (strontium, calcium, barium chlorapatite) being the blue phosphor. Alternatively the RGB phosphor layer consists of 45 w % YOX (yttrium oxide) as red phosphor, 46 w % LAP (Lanthanum phosphate) as the green phosphor and 9 w % BAM (barium magnesium aluminate) being the blue phosphor. The lamp vessel cotained a rare gas mixture of Xe with 50 vol. % Ar with a total fill pressure at a temperature of 200C of 2.0 mbar. The lamp thus operated did not display any instability even when the air temperature was lowered to 25 degrees centigrade.

In comparison a known TLD Master 36W/840 lamp has a phosphor layer of about 4 μm thickness consisting of 57 w % YOX as red phosphor, 36 w % LAP as the green phosphor and 7 w % BAM (barium magnesium aluminate) being the blue phosphor. The thus mixed phosphor layer has a mean particle size of about 3 μm.

The luminous properties and the power savings of a lamp according the invention is compared to that of the TLD Master 36W /840 lamp at ambient temperatures between 25°C and 30⁰C. These temepartures are typical for application circumstances in luninaries. The results of the measurements are presented in figure 2, showing with curve 10 the luminous flux and with curve 20 the power savings in dependency of the ambient temperature which was varied over the range from 25oC and 30oC. So, the lamp according the invention realizes a power saving of about 10% while the lumen output is almost to that of a TLD Master 36W lamp. The invented lamp thus forms an advantageous replacement lamp for the existing prior art lamp. It is observed in this respect that differences in luminous flux of about 5% are not visible and up to 10% are hardly noticeable for a human observer.

Further embodiments of lamps having the same geometry as the TLD Master 36W lamp, with mutually different gas fillings have been tested. The results are shown in the Table.

Table

The 1st column mentions the combined filling pressure of the rare gas filling at 200C. The 2nd column mentions the vol. percentage of the heaviest rare gas of the gas filling, being the Xe. In the column Stability "+" indicates that the lamp operates very stable at 250C well below the 0.2 instability level. The "0" in this column indicates that the lamp operates with some instability still acceptable but somewhere in the region between 0.1 and 0.2 instability level.

In the column Savings a "+" indicates that the lamp, when in operation shows a power saving over the known lamp well over 5%, more particular in the range of 10%. A "0" indicates that the power saving is less significant, however still > 5%.

Claims

CLAIMS:

1. Fluorescent lamp having a lamp vessel comprising a noble gas mixture of Xe and either Ar or Ne.

2. Fluorescent lamp according to claim 1, wherein the noble gas mixture in the lamp contains 30 to 70% Ar and has a filling pressure between about 1.5 and about 3 mbar.

3. Fluorescent lamp according to claim 1, wherein the noble gas mixture in the lamp contains 20 to 60 % Ne and has a filling pressure between about 1.5 and about 3 mbar.

4. Fluorescent lamp according to any of the claims 1 to 3, wherein the lamp vessel has a wall which is provided with a phosphor layer having a mean particle size of about 6 μm.

5. Fluorescent lamp according to any of the claims 1 to 4, wherein the phosphor layer on the lamp vessel wall has a mass of at least 3.5 mg/cm2, preferably about 4.4 mg/cm2.