7.9.3 Back reflection on the lamp. Osram HQI-E 150 W/NDL CL
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on the outer bulb and the socket or the pinch area first need to be measured as stated in the catalogues, see also section 7.1.
However it should be noted that even if the temperatures measured on the outside of the lamp lie within the defined tolerance values, this does not necessarily mean that there is no overheating inside the lamp.
Those surfaces closely surrounding the lamp, such as the reflector neck, diffuser tube and glare shield caps, reflect back on the lamp. Likewise, elliptical reflectors radiate back onto the lamp if the burner is not positioned correctly in the burner point of the reflector.
In these cases the lamps may also suffer damage even if the temperatures measured on the outside of the lamp lie within the defined tolerance values.
The following recommendations are made:
Figure 39: Projection of the condensate by the refl ector
7.9.3. Back reflection on the lamp
To avoid glare, the glare shield caps often used for halogen bulbs or the glare shield rings on lamps with double-sided burners such as HCI ® may not be used. Instead, the glare protection for these lamps is
effected by using e.g. honeycomb filters or “anti-glare baffles” or “hoods” attached to the outside of the
luminaire.
The luminaire design needs to ensure that no radiation is reflected back onto the lamp as this can cause thermal loads on sensitive parts of the lamp which normally leads to unusually early failures. For a lamp with a quartz arc tube, this may lead to the expansion of the tube or to a leak in the pinch area.
The glare can also be reduced by using protected lamps, such as HCI ® -TX/P, because the fact that there is no front glass at the luminaire means that there is no reflex glare on the front glass.
In lamps with ceramic arc tubes, the so-called sealing area at the ends of the capillaries is particularly sensitive: here overheating can lead to increased chemical reactions and then to cracks and lamp failures. A further sensitive component is the lamp’s getter.
To achieve a homogenous colour radiation, facetted and matt reflectors should be used. Diffuser tubes around the lamp are not suitable.
In lamps with a reflector casing, the reflector should be smoothly cut at the opening and should not have a neck.
Sealing area
Capillaries
Reflector nec k
It is more difficult in cases where the reflector itself comprises the outer part of the luminaire. If a reflector neck is used here, e.g. to prevent the emission of light scatter, this leads, e.g. in ceramic lamps to a higher temperature load in the socket-based capillaries.
The extent of the damage depends on the following parameters:
• Extent of the spatial covering of the reflector neck and the capillaries: less is better
• The diameter of the refl ector neck: bigger is better
• Level of reflection of the reflector neck: matt is better than mirrored
• Overall volume of the reflector: bigger is better
Figure 40: Example of a reflector with a reflector neck over the thermally critical parts of the lamp.
To establish whether or not the luminaire design could cause impermissible thermal damage, the temperature
The service lives stated by OSRAM only apply to lamps operated in luminaires that do not reflect back on the lamp. They are based on a switching rhythm
11 h ON, 1 h OFF.
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