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What causes the bulb explosion and what to do about it?

2018-12-17

What causes the bulb explosion and what to do about it?

 

The majority of projectors use high-pressure mercury bulbs. These bulbs produce light by forming an electrical arc between two tungsten electrodes in the burner of the bulb. The burner is made of quartz glass and contains a gaseous mixture, which has an internal pressure of up to 250 atmospheres at temperatures of up to 1,300 degrees Celsius. In certain circumstances, the burner in the bulb may explode. Luckily, projectors are constructed to cope with this possibility and the bulb explosion should not damage the projector. Nevertheless, it is advisable to avoid bulb explosions.

 

What can cause an explosion?

Most explosions happen for one of the following reasons:

 

Manufacturing defect of the bulb

The glass on the burner may be thinner in some places or have a micro rupture as a result of a manufacturing defect. After the bulb is switched on, the internal pressure increases and the weakened glass may not be able to resist this pressure, causing an explosion. Explosions due to manufacturing defects usually occur within the first minutes or hours of operation. This means that this event is covered by the guarantee period of the lamp. It should also happen infrequently, as most manufacturers let their bulbs “burn” for some time before dispatching them from the factory.

 

Mistake during installation – touching the bare bulb with your hand

Never touch a bulb with your bare hands, especially not on the internal side – directly on the burner or its surroundings. This leaves a greasy spot on the bulb, which heats up more than the rest of the lamp. As a consequence of the thermal expansion, there is internal tension between the different temperature points which can be so strong that the glass cracks. This problem occurs more often when replacing bare bulbs than when replacing whole lamp modules. Therefore, we strongly recommend you to use gloves when replacing the bare bulbs.

 

Non-optimal operating conditions

Even if the bulb does not have a manufacturing defect, weak spots may occur on the glass burner of the bulb if the projector lamp is used under non-optimal operating conditions. These may be caused by:

continuous, or very frequent use of the lamp,

mechanical vibration that affect operating or hot lamp,

low temperatures during projector switch on,

frequent switching-on and switching-off the projector,

not leaving enough time for the lamp to cool down after switching off the projector.

 

Insufficient lamp cooling

Especially when the projector is operated in a dusty or smoky environment, the projector dust filters may become clogged, leading to imperfect cooling of the lamp. The projector should detect the overheated lamp in time, switch it off and leave it to cool down. However, this does not always happen and an overheated lamp may crack.

End of lifespan

Lamps in projectors should not be used for as long as possible, but you should change them as soon as the projector begins to announce the end of the lamp lifespan. We strongly recommend that you should not reset the operating hours counter and continue to use the old lamp, because this considerably increases the risk of the lamp explosion. During its operation, the lamp loses material on the main electrodes in the lamp´s burner, which increases the distance between them. Greater the gap between the electrodes, higher the electrical voltage needed to create and maintain the electrical arc. At the end of the lamp´s operating life, the voltage required to create the arc between the main electrodes is so high that during regular operation the ballast in the lamp (device regulating power supply to the lamp) might not be able to supply the necessary voltage. However, the starting electrode will still keep heating the gaseous mixture contained in the burner of the lamp up to the point when the burner may explode.

Projector defect

Bulb explosions can often be caused by defects on the projector, especially when the lamp´s ballast fails. Due to a defect in some part of the projector, the ballast may supply the lamp with incorrect voltage, does not switch off the power supply, or fails to prevent the bulb overheating. If a new bulb explodes in your projector for the second time, by all means you should take the projector to the service to get it diagnosed. The most common causes of lamp explosions are due to the combination of several factors. For example, it could be a combination of using a worn-out bulb, a projector which is often handled, and dust or grease in the filter.

 

How to prevent bulb explosions?

Try to use your projector as much as possible in accordance with the previous advice. We have summarised this information into a clear infographic 10 tips for longer lamp lifespan.

 

What can I do when my lamp breaks?

The burner in the bulb contains a small amount of mercury. Therefore, after a bulb breaks, you need to move the projector to a well-ventilated place and thoroughly ventilate the room where the bulb broke.

Let the projector cool down for long enough.

Remove the lamp cover, take out the lamp module, put it in a box or a strong bag so that the glass shards cannot cut it through. Try to remove as many of the shards from the lamp space as possible.

If there are shards in an inaccessible place in the projector, we recommend you to take the device to a specialist projector service and have it cleaned.


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