WO2005031881A2 - Disinfecting lamp using ultra-violet light emitting diode - Google Patents

Abstract

A disinfecting lamp having one or more diodes emitting UV-C light (LEDs) is described, in which the bandgap from the valence band to the conduction band is set to 4.5 to 4.9 eV, and preferably to 4.7 eV, by the mixture ratio of the semiconductor compounds in the diode, as a result of which the wavelength of the light emitted is between 250 and 280 nm, and is preferably 265 nm, and the light thus has an optimum germicidal action.

Description

LED disinfecting lamp

The invention relates to a disinfecting lamp having one or more diodes emitting UV-C light UV-LEDs.

Light-emitting diodes that produce UV-C light are already known from

European patent application EP A 0 975 929. The wavelength of the UV light, which is determined by the excitation of electrons from the valence band to the conduction band, is stated there to be 380 nm. Light of this wavelength can also be used for sterilization purposes. Also, published US patent application 2002/0088985 describes a semiconductor component emitting UV light that can be used for sterilizing and purifying water. However, the applications known to date of diodes emitting UV light for disinfection and for killing germs have exploited the sterilizing action of UV-C light to only an inadequate degree because the wavelength of the UV-C light produced by the diodes was not set to give the maximum germicidal action. The germicidal action curve (GAC), which is shown in Fig. 1, has been known for some time now and it shows that the maximum germicidal action is obtained from UV light with a wavelength of 265 nm.

It was therefore an object of the invention to develop a disinfecting lamp whose maximum emission of UV-C light is situated between 250 to 280 nm, and preferably at 265 nm. This wavelength can be accurately obtained when the bandgap from the valence band to the conduction band is set in the diode to 4.5 to 4.9 eV, and preferably to approximately 4.7 eV. The invention therefore relates to a disinfecting lamp having one or more diodes emitting UV-C light (LEDs), in which the bandgap from the valence band to the conduction band is set to 4.5 to 4.9 eV, and preferably to approximately 4.7 eV, by the mixture ratio of the semiconductor compounds in the diode. It is possible for the bandgap from the valence band to the conduction band to be set to 4.7 eV by mixing different semiconductor compounds. What are suitable for this purpose are mixtures that contain, for example, InN, InGaN, AlInGaN, A1N or AlGaN. Fig. 3 shows the dependence between the bandgap energy from the valence band to the conduction band, the lattice constants and the wavelength emitted. The comers of the triangle shown represent binary AeN, GaN and InN mixtures while the lines connecting the comers represent ternary mixtures such as AlGaN, AlInN and InGaN in which the proportion of two of the semiconductor constituents vary, and the area of the triangle enclosed by the lines represent the quaternary compound AlInGaN in which the proportions of three of the semiconductor constituents vary. It is immediately apparent from Fig. 3 what the quantitative composition of a semiconductor mixture needs to be for it to have a bandgap from the valence band to the conduction gap of 4.7 eV and thus for it to emit light at a wavelength of 265 nm. Of the semiconductor compounds specified above, Al_xGaι__xN is very particularly preferred. Disinfecting lamps for, for example, purifying water and air are perfectly well known. A distinction is made in this case between three main types of lamp, namely: 1) low- pressure mercury lamps (Philips brandname: TUV), 2) high-pressure mercury lamps (Philips brandname: HOK), and 3) dielectric barrier discharge lamps based on Xe or Xe gasfilled CI (DBD lamps). The wavelength that is cmcial for assessing the disinfecting action of these lamps can be seen from the GAC curve shown in Fig. 1. This curve substantially matches the absorption curve of DNA molecules. It can be seen from Fig.l that radiation of between 200 and 310 nm (UV-C) is highly suitable for disinfection but that radiation of a wavelength of 265 nm is optimum for this purpose. This also explains why, of the disinfecting lamps, it is mercury lamps that are preferred, because the Hg line is at 254 nm and is thus close to the maximum of the GAC curve. If emission spectra for the above-mentioned types of lamp (TUV, HOK and DBD) are compared with the GAC curve, and thus, at the same time, with the disinfecting lamp according to the invention, the effectivenesses that become apparent are as follows: the TUV lamp achieves an effectiveness of 25 to 35% of that of the lamp according to the invention, whereas the effectivenesses of HOK lamps are 10% and of DBD lamps 18%. As well as effectiveness, what is also of great importance is the power density, i.e. the UV-C power per unit length or area, as shown in Fig. 2. This also explains why, despite their relatively low effectiveness, HOK lamps, i.e. high-pressure mercury lamps, are often used, namely because of their high power density. Where light-emitting diodes have already been used for generating UV-C light and hence for disinfecting purposes, they have been the InGaN-based blue LEDs which were developed by Mr. Nakamura of the Nichia company, which have been known since 1995. Even pure GaN can be used for disinfecting lamps but, given its bandgap of 3.4 eV, it emits UV light at a wavelength of only 365 nm. At the present time the effectiveness of pure GaN LEDs is about 20%, but this Figure may double in the future. Added to this is the fact that, by adding aluminum to GaN, the bandgap too is increased and can be raised to 6.2 eV for pure A1N, which corresponds to an emission wavelength of 200 nm. By varying the ratio of Al to Ga, it is possible to set any wavelength of between 200 and 365 nm in an Al_xGaι_-xN LED. Because the lattice constant of A1N and GaN is approximately the same, as Fig. 2 shows, it is expected that increases in effectiveness similar to those possible with pure GaN LEDs may also be possible with AlGaN LEDs in the future, i.e. it may be possible for effectiveness to be improved from the current 20% to 40%. This will make the effectiveness of the LEDs used in the disinfecting lamp according to the invention appreciably superior to the disinfecting lamps (TUV, HOK and DBD) that are being used today. Also, the power density, i.e. the UV-C power per unit length or area, of the AlGaN LEDs is considerably higher than that of TUV, HOK and DBD lamps. Calculating the power density of TUV lamps gives a Figure of 0.04 to 0.16

W/cm², while the power density calculated for HOK lamps is 1.5 W/cm². By comparison, for an effectiveness of 40%, a power that is typical of high-power LEDs of 1 W and a chip size of 1 mm², Al_xGaι_-xN LEDs give an appreciable higher Figure of 40 W/cm². Apart from these advantages, the disinfecting lamp according to the invention having one or more diodes emitting UV-C light also has the advantages that it is free of mercury, that the full intensity of light is available immediately, that it can be dimmed, that the voltages used in it are low and there is thus no danger of electric shocks from it, and that it has a long working life.

Claims

CLAIMS:

1. A disinfecting lamp having one or more diodes emitting UV-C light (LEDs), characterized in that the bandgap from the valence band to the conduction band is set to 4.5 to 4.9 eV by the mixture ratio of the semiconductor compounds in the diode.

2. A disinfecting lamp as claimed in claim 1 , characterized in that what are used as semiconductor compounds are Al_xGaι_-xN compounds.

3. A disinfecting lamp as claimed in claims 1 and 2, characterized in that the wavelength of the UV-C light emitted is between 250 and 280 nm.