The invention relates to a luminaire comprising:
a reflector body with a reflector portion having a reflective surface and
provided with a coating, which coating comprises light-reflecting particles, a substrate side,
and an outer side; and contact means for electrically connecting a light source.
Such a luminaire is known from US-5,905,594. The reflector portion in the
known luminaire is provided with a coating comprising reflecting white particles, for
example polytetrafluoroethylene particles. In the known luminaire the reflective surface is
formed by the coating. The coating has a total reflection of approximately 95% of visible
light, for example originating from the light source. The manufacture of the known luminaire
is a comparatively cumbersome and difficult process. It is a characteristic of the known
coating that it shows substantially exclusively diffuse reflection. Diffuse reflection means
that light is scattered. As a result, a considerable portion of the light does not issue from the
luminaire to the exterior until after multiple reflections against the coating. In spite of the
high total reflection of the coating, a light loss does occur upon each reflection because the
incidence of light on the coating will always involve not only reflection but also absorption
of light. This absorption may be comparatively great because light-absorbing dust particles
deposit themselves on the coating when the coating is exposed to the environment. The
combination of multiple reflections and the increased absorption of light by the dust particles
causes the light losses to increase further. As a result, the known luminaire has the
disadvantage of a comparatively low light output ratio, especially after the coating has been
exposed to its surroundings for some time. The light output ratio of the luminaire is the ratio
of the quantity of light issuing from the luminaire to the quantity of light generated by the
light source. Since the diffusely scattered light is comparatively difficult to shape into a beam
and to direct, the known luminaire with such a diffusely reflecting coating also has the
disadvantage that it is comparatively unsuitable for use in accent lighting.
It is an object of the invention to provide a luminaire of the kind described in
the opening paragraph in which the above disadvantages are counteracted.
According to the invention, this object is achieved in that the luminaire of the
kind described in the opening paragraph is characterized in that the coating comprises a light-transmitting
binder and is substantially free from light-reflecting particles at its outer side.
Since there are no light-reflecting particles at the outer side, but the particles are fully
accommodated in a layer formed by the binder present in the coating, the outer side of the
coating has a comparatively smooth surface. The binder, which transmits visible light, forms
a transparent, light-guiding layer over the light-reflecting particles and over the reflector
portion. It was surprisingly found that not only diffuse reflection, but also a high degree of
specular reflection of visible light occurs at the coating owing to the transparent light-guiding
layer. The high degree of specular reflection means that substantially all light originating
from the light source issues from the luminaire to the exterior directly or after only one
reflection. As a result, there is hardly any light loss owing to reflection against the coating, as
in the known luminaire, and the luminaire according to the invention has a comparatively
high light output ratio. It was found that light-absorbing dust particles adhere less readily to
the coating because the surface of the outer side of the coating is comparatively smooth, so
that also the light output ratio of the luminaire decreases comparatively little during its
operational life. In addition, the luminaire according to the invention is suitable for use in
accent lighting because of its coating with a high degree of specular reflection.
In a first advantageous embodiment the reflective surface of the reflective
portion is partly formed by the coating according to the invention. This can be realized in that
the reflector portion has at least an area which is free from the coating or wherein the coating
is partly covered, for instance with a further coating having optical properties different from
those of the said inventive coating. It is thereby enabled that the area can be given other,
desired optical properties, for example, the area can be either left blank or alternatively that
the further coating provides for different reflective properties. The further coating may be
provided over the previous applied inventive coating comprising the transparent light-guiding
layer. By selection of the number, the position, the dimensions and the optical properties of
the area, it is possible to obtain the reflector portion having its reflective surface being
optimized for a selected purpose.
In a further embodiment, the light-reflecting particles in the coating of the
luminaire are present in a quantity of ≤ 75% by volume with respect to the quantity of binder.
Owing to the comparatively low percentage by volume of the particles with respect to the
binder, the particles have the possibility of settling on or adjacent the substrate side during a
drying process of the coating, for example in that they have a higher specific mass than the
binder. It is thus achieved in a comparatively simple manner that the particles are fully
enclosed in a layer formed by the binder present in the coating. Another favorable possibility
for obtaining the transparent light-guiding layer over the light-reflecting particles is formed
by a dual-layer or multilayer coating, for example with a light-transmitting layer at the outer
side which is substantially free from light-reflecting particles and a further layer containing
light-reflecting particles between the light-transmitting layer and the substrate side of the
coating.
In a further embodiment of the luminaire, the light-reflecting particles are
surrounded by a pigment skin. This was found to cause a further improvement in the specular
reflection of the coating. To improve the specular reflection still further, the pigment skin and
the light-reflecting particles preferably have different refractive indices. A suitable pigment
skin was found to be aluminum oxide.
Experiments have further shown that light-reflecting particles chosen from the
group formed by halophosphates, calcium pyrophosphate, strontium pyrophosphate, and
titanium dioxide are highly suitably for the coating. These light-reflecting particles can be
very well combined with the light-transmitting binder, for example a silicone binder, a fluoro
polymer (for example THV 200), or acrylate. A luminaire provided with a coating of such a
composition of particles and binder on its reflector portion has very good light-reflecting and
beam-shaping properties.
Obviously, the type of electric lamp is immaterial to the invention. The lamp
may be an electric discharge lamp or an incandescent lamp. The electric element, an
incandescent body in the case of an incandescent lamp, may be accommodated in an inner
envelope in the lamp vessel. In the case of a halogen incandescent lamp, the lamp vessel will
contain a halogen-containing filling, in the inner envelope, if present. The inner envelope is
usually present if the electric element is a pair of electrodes in an ionizable gas.
It is further noted that WO 99/13013 discloses a reflector body with a light-reflecting
carrier manufactured from metal, i.e. aluminum, on which a transparent coating is
provided. The coating of the reflector body comprises a transparent binder and transparent
particles, for example of silicon dioxide. The granular surface structure of the coating has the
effect that the known reflector body has not only specular reflection owing to the aluminum
carrier material but also a certain degree of diffuse scattering of the light incident on the
coating. The known reflector body has the disadvantage of a comparatively low total
reflection of approximately 83%.
Embodiments of a luminaire according to the invention are diagrammatically
shown in the drawing, in which
Fig. 1 shows a first embodiment in perspective view; Fig. 2 shows a detail of the coating of the luminaire of Fig. 1 in cross-section;
and Fig. 3 shows a second embodiment in perspective view.
Fig. 1 shows a luminaire with a reflector body 1 having a concave reflector
portion 2, an elongate asymmetrical concave reflector in the Figure, with a reflector axis 4,
having a reflective surface 200, said reflector portion 2 being provided with a lightguiding/reflecting
coating 3. In the described embodiment the reflective surface 200 is
formed by the coating 3. Contact means 5 are provided in the concave reflector portion 2 for
the electrical connection of an electric lamp 6 with a light source 7. The electric lamp 6 in the
Figure is a high-pressure gas discharge lamp, for example a HPI-T 250W type, which is
placed in a luminaire according to the invention, for example a Philips MPF 211 type,
provided with the coating 3. The light source 7 is positioned on the reflector axis 4 of the
reflector portion 2. The coating 3 has a total reflection of more than 95%. Luminaires
according to the invention have a light output ratio of approximately 89%, whereas
corresponding conventional luminaires, such as the Philips MPF 211, have a light output
ratio of approximately 74%. After a period of time, i.e. at the 800-hour operational life
moment, a light output ratio of approximately 88% was measured, i.e. a decrease in the light
output ratio of the luminaire according to the invention of no more than approximately 1%
over this period. The reflection of luminaires according to the invention is partly diffuse,
partly specular. As a result, luminaires according to the invention provide a light distribution
with comparatively well defined contours, with a comparatively narrow beam, and with a
comparatively high intensity, for example with a top value for the intensity of approximately
800. The top value obtained with corresponding conventional luminaires is approximately
650, standardized to a same scale. The luminaire as shown in the Figure is highly suitable for
canopy lighting in closed ceilings such as, for example, in gas filling stations.
Fig. 2 shows a detail of the coating 3 of the luminaire of Fig. 1 in cross-section.
The coating has light-reflecting particles 10, a light-transmitting binder 11, a
substrate side 12, and an outer side 13. The light-reflecting particles 10 are positioned
adjacent the substrate side 12 in the coating 3, and the coating 3 is substantially free from the
light-reflecting particles 10 at the outer side 13 because there is a light-transmitting layer 15
at the outer side 13. It is visible in the Figure that the coating 3 is mainly formed by the
binder 11 and that the light-reflecting particles 10 account for approximately 25% by volume
with respect to the volume of the coating 3. The light-reflecting particles 10 are titanium
oxide particles, having a reflection index of 2.32, which are provided with a pigment skin 14
of aluminum oxide, having a reflection index of 1.63; such coated particles are commercially
available, for example under the trade name Kemira 675. The binder is a silicone binder, for
example RTV 615. The coating 3 is provided on the reflector portion through spraying of a
suspension comprising the binder 11, the light-reflecting particles 10, and a solvent, for
example cyclohexane. Then the coating is dried in the air for approximately 45 minutes at a
temperature of approximately 130 °C. The light-reflecting particles 10 deposit themselves at
the substrate side 12 of the coating 3 during drying.
Fig. 3 shows a second embodiment of the luminaire of the invention in which
the reflective surface 200 is partly formed by the coating 3. In the embodiment the reflective
portion 2 has two areas 20, being provided with a further coating, being a specular reflective
coating, this further specular reflective coating being aluminum. Because of the specular
reflective areas 20 in the luminaire, compared to the luminaire of Fig. 1, the light distribution
of the luminaire of Fig. 3 has even better well defined contours, with a narrower beam, and
with an increased intensity. Under circumstances, variations in the areas 20 in the luminaire
of Fig. 3 might lead to a light output which is fractionally lower light output than the light
output of the luminaire of Fig. 1. However, this fractionally lower light output is by far
outweighed by obtainable improved properties, i.e. in the luminaire of Fig. 3 the increased
intensity of the narrower beam. Said improved properties are of interest for applications of
the luminaire of Fig. 3 for canopy lighting in closed ceilings such as, for example, in gas
filling stations. The narrower beam having a top value for the intensity of the light
distribution up to approximately 950 compared to a corresponding value of 800 for the
luminaire of Fig. 1, standardized to a same scale.