What causes a bulb to explode and what can be done 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 bulb burner. The burner is made of quartz glass and contains a gaseous mixture with 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 have been constructed with this possibility in mind and therefore bulb explosion should not damage the projector. Nevertheless, it is advisable to avoid such explosions.

What can cause an explosion?

Most explosions happen for one of the following reasons:

Bulb manufacturing defect

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 withstand the pressure, which in turn causes an explosion. Explosions due to manufacturing defects usually occur within the first minutes or hours of operation. This means that such event is covered by the lamp’s warranty. Also, this is not likely to happen very often since 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 directly on the burner or parts around it. This leaves a greasy spot on the bulb, which causes it to heat up more than the rest of the lamp. As a consequence of thermal expansion, internal tension between the different temperature points can be so strong that the glass cracks. This problem occurs more often when replacing bare bulbs than when replacing the lamp with housing as a whole. Therefore, we strongly recommend that you use gloves when replacing a bare bulb.

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;
• a mechanical vibration that affects functioning or causes a hot lamp;
• low temperatures when the projector is switched on;
• frequently switching the projector on and off;
• not leaving enough time for the lamp to cool down after switching the projector off.

Insufficient lamp cooling

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

End of lifespan

A projector lamp should not be used indefinitely and that’s why the lamp should be replaced as soon as the projector signals that the end of the lamp lifespan is nearing. We strongly recommend not to merely reset the operating time counter and to continue using the old lamp, because this considerably increases the risk of a lamp explosion. During operation the lamp loses material on the main electrodes in the lamp’s burner, which increases the distance between them. The greater the gap between the electrodes, the 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 the 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 to the point where the burner may explode.

Projector defect

Bulb explosions are often caused by projector defects and this is especially the case if the lamp’s ballast fails. Due to a projector defect, the ballast may supply the lamp with an incorrect voltage, fail to switch off the power supply or prevent the bulb from overheating. If a new bulb explodes in your projector for the second time, by all means you should take the projector to get serviced. The most common causes of lamp explosions are a 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 in a clear infographic: 10 tips for a 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 housing, put it in a box or a strong bag so that the glass shards cannot cut through it. Try to remove as many of the shards from the area around the lamp as possible.

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