A luminaire housing which has a base portion closed in a water-tight manner by a cover which is at least in part transparent. The wall of the base portion has a venting opening located in the bottom of a depression. This depression has a side wall extending obliquely around the bottom, and an outwardly directed collar surrounding the venting opening. At an area located opposite to the venting opening, a wall portion of the cover is removable to provide a drainage opening. A labyrinth around the drainage opening on the inner side of the cover prevents any water and dust which may enter through the drainage opening from spreading through the housing.

BACKGROUND OF THE INVENTION 
The invention relates to a luminaire comprising a housing which 
accommodates a holder for an electric lamp. The housing has a base portion 
which is closed by a cover which is at least in part transparent, and a 
venting opening provided in the wall of the base portion. 
Such a luminaire is known from German Gebrauchsmuster No. 1940617 and is 
frequently used to illuminate moist spaces. Due to the presence of venting 
openings, the temperature in the housing is prevented from increasing to 
an excessively high value during operation of a lamp arranged in the 
luminaire. In the housing of this luminaire, a comparatively large number 
of venting openings are provided through the base portion. These openings 
are in the form of slots formed in special spacer lugs, by means of which 
the housing can be secured to a ceiling. This construction, according to 
the Gebrauchsmuster, prevents water flowing into the housing, when the 
housing is secured to the ceiling. However, it has been found that, when 
such a luminaire is mounted on a wall in a position deviating from the 
horizontal, such as on a vertical wall, there is a risk nevertheless that 
water enters the housing and cannot escape. 
This is especially disadvantageous in luminaires comprising a housing of 
comparatively small dimensions. It has been found that water and dust can 
then readily reach the current-conveying parts in the housing. Thus this 
known luminaire does not satisfy international standards with respect to 
water- and dusttightness (for example IP 54, as described in the document 
CIE 598-1 (1979)). 
SUMMARY OF THE INVENTION 
The invention has for its object to provide a luminaire in which, when 
secured either to a ceiling or to a vertical wall, the accessibility of 
water or dust is rendered difficult. 
In accordance with the invention, in a luminaire of the kind mentioned in 
the opening paragraph a venting opening is provided in the bottom of an 
inward depression in the base portion. This depression has a side wall 
extending around the bottom, while the venting opening has an outwardly 
directed collar rising above the depression bottom. At an area located 
opposite to the venting opening, the cover has a wall portion which can be 
removed to provide a drainage opening. A labyrinth around the drainage 
opening, on the inner side of the cover, prevents any water and dust, 
which may enter through the drainage opening when the wall portion has 
been removed, from spreading through the housing. 
The luminaire according to the invention provides, independently of the 
position in which it is mounted, a sufficient screening from penetration 
of dust and water. It satisfies the international requirements imposed 
with respect to dust- and watertightness. Due to the presence of the 
venting opening in the base portion, the seal between the base portion and 
the cover (which seal consists, for example, or a rubber ring) is 
prevented from being loaded by to a pressure difference between the air 
inside and outside the housing. If the base portion of the housing is 
secured to a vertical wall, venting is obtained through the opening in the 
base portion. The cover is then not provided with a drainage opening. The 
presence of the collar around the venting opening and the wall of the 
depression, which is preferably slanted for easy manufacture, prevents 
water (or any other liquid), which might reach the depression in the base 
portion from entering the housing through the venting opening. 
On the other hand, if the housing is secured to a generally horizontal 
ceiling, it is possible that water reaches the venting opening from the 
ceiling and enters the housing. When the luminaire is installed in this 
position, the removable portion in the housing then should be removed by 
the user to form a drainage opening. This wall portion may, for example, 
be a rubber plug or a frangible region in the cover. The water entering 
the base portion through the venting opening drops downwards and leaves 
the housing through the drainage opening located opposite to the venting 
opening. In order to prevent water or dust nevertheless spreading through 
the housing, the labyrinth or a similar screening is provided near the 
drainage opening. This labyrinth is preferably constructed as a set of 
walls extending from the depression in the base portion and from the 
cover. Thus, it is prevented that water or dust, entering through the vent 
opening, spreads from the cover portion surrounding the draining opening 
in the housing and reaches the current-conveying members located in this 
housing. 
In a preferred embodiment of the luminaire according to the invention, a 
labyrinth screening around the drainage opening comprises a first tubular 
part which faces the base portion and is integral with the cover, and a 
second tubular part extending in the direction of the cover from around 
the venting opening in the base portion. The first tubular part has a 
larger diameter than the second tubular part and these tubular parts 
overlapping each other longitudinally, thereby forming an annular gap 
between the walls of the tubular parts. A tubular wall part is also to be 
understood herein to mean a wall portion which, for example, has a 
rectangular cross-section. 
By a suitable choice of the dimensions of these tubular parts, it is 
prevented that water jets from the outside directed to the drainage 
opening reach the interior of the housing. Experiments have shown that 
water jets which are incident at an acute angle to the cover and which are 
directed with great force to the drainage opening do not penetrate into 
the space in the interior of the housing. The present embodiment further 
has the advantage that a satisfactory screening is obtained from dust 
penetrating through the openings. 
In a particular embodiment of the luminaire according to the invention, the 
depression in the base portion, in which the venting opening is formed, is 
located in an inwardly offset part of the base portion, while a collar is 
present which surrounds the depression. Especially when the housing is 
secured to a ceiling, the possibility of water entering through the 
venting opening is further reduced. 
The luminaire according to the invention preferably comprises a housing of 
synthetic material or of aluminum and is particularly suitable to receive 
a light source having comparatively small dimensions, such as a "PL" lamp 
(cf. for example German Offenlegungsschrift No. 3121077 to which U.S. Pat. 
No. 4,426,602 corresponds. 
An embodiment of the luminaire according to the invention will be described 
more fully by was of example with reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The luminaire shown in FIG. 1 comprises a housing (1) of synthetic material 
having a base portion (2) which is closed in a water-tight manner by means 
of an elastic sealing ring or gasket 2a (cf. FIG. 2) and a cover 3, which 
comprises a transparent window 4. The housing further accommodates a 
holder for an electric lamp (not shown in the drawing). The lamp is, for 
example, a compact luminescent low-pressure mercury vapor discharge lamp, 
whose discharge vessel comprises two tube portions which are arranged 
beside and parallel to each other and are interconnected (cf. 
Offelegungsschrift No. 3121077 or U.S. Pat. No. 4,426,602). The housing 
further has room for an electric stabilization ballast, which is required 
for the operation of the lamp. The front wall of the cover 3 has a 
frangible region which can be removed by a user to form a drainage opening 
5. 
FIG. 2 shows the situation in which the housing of the luminaire is secured 
to a horizontal ceiling 6. The base portion 2 is provided with an inward 
depression 7 (of circular cross-section) having a bottom 8 with a sidewall 
9 extending obliquely with respect thereto. The bottom 8 is provided with 
a venting opening 10 which has an outwardly directed collar 11. The cover 
3 is provided with the drainage opening 5, which in this luminaire 
orientation is below the venting opening 10. In the situation shown in 
FIG. 2, the opening 5 is located substantially perpendicularly below the 
venting opening 10. The drainage opening 5 is obtained when the frangible 
region in the cover 3 is pushed away by the user. Near the drainage 
opening 5, a labyrinth of overlapped walls is provided on the inner side 
of the cover 3 in order to prevent any water and dust which may enter 
through opening 5 from spreading through the housing. Around the drainage 
opening 5, a first tubular part 12 is arranged, faces the base portion 2 
and which is integral with the cover 3. A second tubular part 13 extends 
from a region around the venting opening 10 towards the cover. The tubular 
part 13 is integral with the base portion 2 and also consists of synthetic 
material. The tubular parts 12 and 13 have different diameters (the inner 
diameter of 13 is smaller than that of 12), and overlap to form an annular 
gap 14. As appears from FIG. 2, the ratio between the diameters of these 
tubular parts and the extent to which they overlap each other are chosen 
so that even a high velocity water jet which is directed into the opening 
5 from the outside at an oblique angle, is still screened. In this 
construction, water and dust are prevented from spreading through the 
housing. 
The depression 7 in the base portion 2, in which the venting opening 10 is 
formed, is located in an inwardly offset part 15 of the outer wall of the 
base portion. A cylindrical upright edge 16 is present around the 
depressions 7. As a result the possibility of water flowing into the 
housing through the venting opening 10 is further reduced. In the case in 
which, besides the upright edge 16, also the collar 11 in the depression 7 
is overflown by water, a further spread thereof through the housing need 
not be feared. In fact the water then drops downwards and reaches the 
space which is bounded by the cylinder 12 and the hood 3 and is provided 
at its lower side with the drainage opening 5. This opening is preferably 
larger than the venting opening 10. A satisfactory drainage of the water 
is then guaranteed. 
As appears from the construction of the base portion, during operation in a 
vertical position, the venting opening 10 is not closed by water. This is 
prevented due to the oblique sidewall 9 and due to the collars 11 and 16. 
The water flows away over the oblique sidewall 9 and the gap between the 
ceiling and the end of the base portion. 
In a practical embodiment, the housing of the luminaire has a length of 
about 40 cm, and a width of about 15 mm. The inner diameter of the tubular 
part 13 is 16 mm and that of the tubular part 12 is about 29 mm. The 
height of the tubular part 12 is 17 mm and that of the tubular part 13 is 
about 20 mm. These tubular parts overlap each other by 11 mm. In the state 
in which the outer side of the base portion is secured to the ceiling by 
means of screws, for example, the botton of the depression is located 
about 10 mm below this ceiling. The collar 16 has a height of 1.5 mm. The 
wall portion 15 is located 6 mm below the ceiling. This luminaire 
satisfies the water- and dust-tightness standard IP54 according to 
CIE-598-1.