Luminaire

Details Luminaire Luminaire

1998-01-23

2001-06-26

Quach, Y. (Department: 2875)

Illumination

Plural light sources

Particular wavelength

C362S240000, C362S245000, C362S800000

Reexamination Certificate

active

06250774

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a luminaire comprising a housing with a light emission window, and at least one lighting module for illuminating an object accommodated in the housing and comprising a light source and optical means.
Such luminaires are generally known and are used, for example, for street lighting, for lighting a portion of a street, or in spotlighting, for example for lighting objects in shop windows.
A luminaire for street lighting of the kind described in the opening paragraph and fitted with two lighting modules is known from DE 44 31 750 A1. The first lighting module is designed for illuminating a surface portion of the road which extends to comparatively far away from the luminaire. The second lighting module is designed for illuminating a surface portion close to the luminaire. The light sources of the luminaire can be controlled independently of one another so as to illuminate a road section optimally both in wet and in dry weather. The lighting modules in the known luminaire each have a tubular discharge lamp as the light source and a reflector as the optical means. A disadvantage of such a luminaire is that the light from the light sources is difficult to concentrate into a beam. More than 50% is often incident outside the object to be illuminated in practice.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a luminaire in which the light generated by the light source is utilized more efficiently.
According to the invention, the lighting module comprises a set, for example a few dozen, of lighting units which each comprise at least one LED chip and an optical system cooperating therewith, the LED chips and optical systems forming the light source and the optical means, respectively, while the lighting units illuminate portions of the object during operation, and the LED chips each supply a luminous flux of at least 5 lm during operation.
An LED chip comprises an active layer of a semiconductor material, for example AlInGaP or InGaN, which emits light upon the passage of a current. Integrated units of an LED chip and a primary optical system are generally known under the name of LEDs (Light Emitting Diodes), also referred to as LED lamps. The surface area of the active layer of an LED chip is comparatively small, for example of the order of a few tenths of a mm
2
up to a few mm
2
. An LED chip thus forms a good approximation of a point source, so that the light generated thereby can be easily and accurately concentrated into a beam. Since the LED chips jointly illuminate the object, each individual beam only hitting a portion of the object, the beams may be narrow, so that they can be aimed with high accuracy within the boundaries of the object and only little light is incident outside the object. The use of LED chips which each supply a luminous flux of at least 5 lm during operation results in a luminaire according to the invention which, in spite of a comparatively limited number of lighting units, yet offers wide application possibilities, for example for street lighting, spotlighting, or floodlighting. The light distribution may be adjusted in a flexible manner through a control of the luminous fluxes of lighting modules or of separate lighting units of a lighting module.
If so desired, the portions of the object to be illuminated may overlap one another so as to achieve a more homogeneous lighting result, for example illuminance or luminance. Overlaps of the portions to be illuminated may also be desirable for achieving an even light distribution. A measure for the overlaps is the overlap factor (O) defined as O=(&Sgr;&OHgr;
e
−&OHgr;
a
)/&OHgr;
a
where &Sgr;&OHgr;
a
is the sum of the beam angles of the lighting units, and &OHgr;
a
is the optical solid angle covered by the object to be illuminated with respect to the luminaire. The beam angle of a lighting unit is defined here as the solid angle of that portion of the beam generated by the lighting unit within which 65% of the luminous flux of the lighting unit is contained and within which the luminous intensity is greater than or equal to that outside it. A lighting unit may illuminate portions of the object remote from one another, for example as a result of components which split up the beam of the lighting unit. In that case the beam angle is the sum of the solid angles of those portions of the beam within which in total a 65 % fraction of the luminous flux of the lighting unit is contained and within which the luminous intensity is greater than or equal to that outside said portions. The overlap factor is preferably at most 10 in a fully illuminated object. The homogeneity of the lighting result increases only little when the overlap factor increases further. The ratio of the overlap factor (O) to the number of lighting units (N) is preferably below 0.2. At a higher ratio, comparatively strongly widening beams are necessary, so that the light generated by the luminaire can be aimed less efficiently within the boundaries of the envisaged object and the possibilities of varying the distribution of the illuminance are limited.
It is favourable when the LED chips generate light mainly in a wavelength range from approximately 520 nm to approximately 600 nm for applications where the luminous efficacy plays a major role and colour rendering is of lesser importance, for example for lighting of roads and garages. LED chips may be used for this purpose, for example comprising an active layer of AlInGaP with an emission maximum at 592 nm. A combination of red-, green-, and blue-emitting LED chips may be used in applications where on the contrary the colour rendering is important, such as lighting of domestic spaces, for example LED chips having an active layer of AlInGaP for emission in a wavelength range of 590-630 nm, and LED chips with an active layer of InGaN for emission in the wavelength ranges of 520-565 nm and 430-490 nm. The active layers of a red-, a green-, and a blue-emitting LED chip may then be provided on a common substrate, for example made of sapphire or silicon carbide, and these LED chips may have a common optical system. Alternatively, for example, lighting units may be used in which the LED chip emits UV radiation and the optical system of the lighting units comprises means for converting UV radiation into visible radiation. The means for converting UV radiation are formed, for example, by a luminescent layer provided on the LED chip.
An attractive embodiment of the luminaire according to the invention is characterized in that the set of lighting units comprises two or more varieties of lighting units for illuminating portions of the object with mutually differing spectra. The spectra of the lighting units may then be adapted to the optical properties, for example the reflectivity, of the individual portions of the object, so that an optimum visibility of these portions is realized. The different spectra in addition render it easy for an observer to orient himself.
The luminance often lies in the mesopic vision range in the case of outdoor lighting such as street lighting, safety lighting, and lighting of parking lots, i.e. between 0.001 and 3 cd/m
2
. The eye sensitivity to light originating from the periphery of the field of vision under these circumstances is a maximum for a wavelength which is relatively short, approximately 510 nm, compared with a wavelength, approximately 555 nm, for which the eye sensitivity to light coming from the center of the field of vision is a maximum. A modification of the preceding embodiment which is particularly favorable for outdoor lighting is characterized in that the set of lighting units comprises a first variety of lighting units for illuminating central portions of the object with a spectrum having a maximum at a first wavelength and a second variety of lighting units for illuminating peripheral portions of the object with a spectrum having a maximum at a second wavelength which is smaller than the first wavelength. This modification is particularly suitable for road lighting, the

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