cavitation in metal halide bulb

[cmcgill]

I have a relatively new system, less than two years old. It is ~420 gal and sits on a table ~10' x 4'. I have two 400 W metal halide bulbs on this system. Approx 1 foot above the lights is a "topper." I work at a research facility and this table was previously designed for another use which is why this topper is on there. The topper covers the entire table and has one large opening that was previously used has a duct opening. I tried to have the topper removed some time ago but was met with some resistence. Obviously, I lost because the topper is still there. At any rate, the first set of bulbs I had on the system I had no problems with. I changed them at one year. The second set of bulbs I put on have both burnt out and when I removed the bulb, both had a cavitation in the glass with a little pin hole in the midde. I use Icecap 400 W ballasts and Iwasaki 400 W 6.5 K bulbs. After speaking with my bulb supplier, they suggested it wasn't the bulbs but an overheating issue. I wanted to get a second opinion. My first thought was the supplier is trying to say it's not the product but what they said makes sense considering I have the topper on the system. I just want to be sure before I re-visit the issue of removing the topper. Thanks.

 

[sirreal63]

It is entirely possible that heat caused that. I would know better with a pic of the setup, including how close the bulb is to the reflector. 12" should be enough clearance for the shelf above, but if the bulb is too close to the reflector, it could happen, though I have never seen a bulb do that.

 

[Purple Rocks]

If the cavitation occurred on the side facing the reflector this could possibly be the issue, Reflectors can cause hot spots , reflecting light at many angles into a single point. The pin hole and cavitation is a result of the vacuum pulling air in at the weakest/hottest point.

I believe this is the problem, the combined heat of the bulb + small space between reflector + no air movement + hot spot = Equipment failure.

Both went same time, same problem? Its not the equipment or the bulb. IMO
Reflectors reflect light and HEAT.

I would suggest to increase the gap between the light and the reflector, check for any dents on the reflector (these can cause hot spots), increase air movement, or change manafacturer of bulb some bulbs are long and cylindrical others have a buble in the centre, i believe this bubble can help to eleviate hot spot issues, it also stregthens the glass and forces the user to keep a greater distance from the reflector.

This is just my 2 cents and hope it helps alittle. Good luck !