Note: Descriptions are shown in the official language in which they were submitted.
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WO 99/58900 PCT/NL99/00261
A LIGHT HOUSING PROVIDED WITH AN AFTERGLOWING COATING,
THE COATING USED FOR THAT PURPOSE AND THE COATING METHOD
USED FOR THAT PURPOSE
The invention relates to a light housing, such as a
light box or a light source of an at least partially
transparent material.
The term light source as used herein is understood to
mean an incandescent lamp or a tube lamp, for example,
and the term light box is generally understood to mean a
light casing, a lamp shade or other devices which
enclose a light source at least partially.
A normally operating, energized light source generally
emits "white" light. When the current supply to the
light source is interrupted, for example in case of a
power failure caused by calamities, such as the blowing
of a fuse, fire and the like, or when part of the light
source just breaks down, for example when a filament
burns through, or when the light source is turned off,
the room darkens. When such darkening is undesirable,
numerous problems may arise. Generally, persons who were
carrying out activities in such a room cannot resume
their activities until the light source emits light
again, for example. In particular in case of an
emergency, such darkening generally leads to panic
reactions and the persons have difficulty in getting
their bearings in the dark, in particular when they have
to leave said rooms. Usually it will be necessary in
such situations to revert to the use of light sources
which operate independently of a power source, for
example pocket lights and candles.
It is an object of the present invention to obviate the
above drawbacks. To that end, the invention provides a
light housing which is at least partially provided with
an illuminating coating.
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When the current supply to a light housing according to
the present invention is interrupted, visible light will
still be emitted, due to the action of the illuminating
pigments, at positions where such a light action is
expected, namely by the light source itself or by a
light box enclosing said light source. Thus, it is not
necessary for the persons who are present in such a room
to remedy the calamity at once, since the light that is
still being emitted is sufficient to enable them to
1.0 complete the normal activities. In case of a dangerous
situation, such as a fire, people can leave the room
without any problem, since a sufficient amount of light
is still available. Possible panic reactions are
suppressed in this manner.
The invention thus provides a safe and secure solution
for the problems which may arise in case of undesirable
darkening.
The term afterglowing pigment as used herein is
understood to mean a fluorescent and/or phosphorescent
pigment. Fluorescence is the process whereby radiation
is emitted as a result of a transition between molecular
energy levels exhibiting the same spin condition, whilst
in the case of phosphorescence, radiation is emitted as
a result of a transition between two molecular energy
levels exhibiting different spin conditions.
Fluorescence is of very short duration, and generally it
only occurs visibly when a fluorescent pigment is
exposed to light. Phosphorescent pigments, however, are
capable of emitting light for a much longer period of
time after being exposed to light, however. Another
advantage of fluorescent as well as of phosphorescent
pigments is the fact that they are both capable of
emitting light of a different wavelength or a different
wavelength range than the light to which they are
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exposed, or to which they were initially exposed. Such a
pigment is thus capable of emitting light of a
particular colour or tint upon or after exposure to for
example "white light".
Illuminating pigments are activated by natural light or
by other light sources. In the dark, for example in case
of a power failure, the absorbed light is immediately
emitted. This makes it possible within the framework of
passive safety to use said photo-illuminating light
housings as signal generators in case of the above
calamities, such as a power failure. An additional
advantage of such light housings is the fact that the
light from the light source is directly absorbed by the
photo-illuminating pigment. When the natural light
becomes dimmer or when the light sources are
extinguished, actively or not actively, the pigment will
start to emit the absorbed light.
A light housing according to the invention is in
particular provided with a coating consisting of a
dispersion with a base of cellulose, acrylate, epoxy or
polyurethane, or of a foil, for example a shrink foil
provided with an afterglowing pigment of a alkaline-
earth metal-containing aluminate, which is doped with
one or more transition metals.
Such a coating can be applied thinly, since said
illuminating pigments have a small grain size of
approximately 7 - 10 ~Cm.
The afterglowing or illuminating pigment can be exposed
to light having a wavelength range of about 350 - 450 n,
preferably of about 380 - 400 nm. The afterglowing
pigment preferably emits light wherein the wavelength
maximum lies at about 520 nm and the wavelength range of
the emitted light is about 475 - 575 nm.
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The persistence and the intensity of the afterglow in
accordance with Din 67510, Part 4 (1995) of the
afterglowing pigment is at least 1,350 minutes,
preferably at least 2,000 minutes with a visibility
limit of 0.3 mcd/ms. The intensity of the light being
emitted by the afterglowing pigment after 5 minutes is
at least 170 mcd/mz, preferably at least 400 mcd/m2,
after 30 minutes it is at least 25 mcd/ms, preferably at
least 65 mcd/mz, and after 20 minutes it is at least 5
mcd/ms, preferably at least 11 mcd/ms.
The the light housing according to the invention is
preferably provided with a coating wherein the charging
degree of the afterglowing pigment is 10 - 80%,
preferably 20 - 50%. This provides a perceivable light
intensity for a duration of at least 8 hours, which
makes it possible to find the exits when darkness sets
in or when the lights go out due to a calamity.
A light housing according to the invention preferably
comprises a coating having a layer thickness of 10 - 100
~.m, for example 50 ~,m.
The coating according to the invention is particularly
suitable for being used as an outer layer on a
prefabricated light housing. The provides the additional
advantage of protection against breakage, for example in
the case of glass fracture of a light source, whereby
fragments of glass that may have come loose are
confined.
Such a thin layer will not visibly interfere with the
light emitted by the light source, so that the
transparency remains ensured.
In case of an interruption in the power supply, the
initial light output of the light housing according to
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the invention will preferably be at least higher than
3,000 mcd/mz, more preferably at least 5,000 mcd/m2.
One preferred embodiment is a light housing according to
the invention in the form of a fluorescent tube. Since
such a fluorescent tube has a large surface area, a
substantial afterglow action can be obtained due to the
action of the large surface area of the coating. For the
same reasons, the generally known energy-saving lamps
constitute a preferred embodiment of a light housing
according to the invention.
The invention furthermore relates to an illuminating
coating with a base of a dispersion, for example a
cellulose, acrylate, epoxy or polyurethane dispersion or
a foil provided with an afterglowing pigment of an
alkaline-earth metal-containing aluminate, which is
doped with one or more transition metals, and to a
method of applying such a coating to a light housing.
The coatings, for example with a base of a polyurethane
dispersion or another plastic emulsion or dispersion,
are directly applied to the glass of the light housing,
the light source or the light box by dipping or by using
another application technique. Said coated light sources
can be fitted in the usual light boxes or lamp holders.
A coating with a base of a foil of LDPE or PE, for
example, preferably a shrink foil, for example of
modified vinyl acetate, can be applied to the light
housing directly after the manufacture thereof as a
subsequent finishing step. The advantage of using a
shrink foil is that a tightly fitting, dust-proof and
moisture-proof illuminating coating is obtained.
The light housings may first be subjected to a pre-
treatment step, for example an etching step or another,
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mechanical operation, such as blasting or sanding. The
application of a primer may render such a pre-treatment
step superfluous.
A uniform coating is applied to the glass in a layer
thickness of approx. 10 - 100 ~,m by dipping, after which
drying and curing follows. A layer thickness of 20 - 70
~Cm is preferred. Such a thin coating disturbs the normal
light action only minimally. Said dipping may take place
in two directions, so as to obtain a homogeneous
coating. According to to technique, the light source,
such as a tube, a lamp etc. is rotated horizontally in
the coating, thus obtaining a uniform coating in one
operation. This coating can only be applied by means of
a paint brush or by using a spraying technique.
Possibly, the coating may be provided with a colourless
finishing layer.
