[Finagleabud]

I have a brand new 400w Plantmax HPS bulb which somehow got scratched slightly in my move accross country. The scratch looks very shallow, but is visible to the naked eye. What is the likelihood this will cause the bulb to explode? Should I just replace it? I'm super paranoid when it comes to safety.

[rives]

Good call. Get rid of it, unfortunately. Normally the packing on lamps (at least for the industrial market) warn against envelope failure as a result of scratches and fingerprint oil breaking down the glass.

[poindexterous]

The fears of bulb explosion are vastly exaggerated. And a scratch is the least thing to worry about. Every HID bulb I've ever tossed due to age or lost lumens, both HPS and MH, dozens, I've shot with my BB gun and they don't explode, ever, far from it, BB passes through just leaving small hole in both outer glass and inner gas tube, and the bulb still stays in one piece. The first time I tried it I expected some huge explosion having heard all the bulb myths, it was anti-climactic, I was disappointed, I had worn goggle for nothing, lol.

Once I had a fully hot bare 1000 MH bulb running and accidentally plugged in a sump pump below it shooting a 20gpm geyser of 50 degree water onto it and it stayed running just fine and not a crack, I was shocked(mentally not electrically). I touch my bulbs bare handed all the time, bugs die on them, goo drips on them, all kinds of bad stuff, never once ever had one break before the BB gun retirement.

It's always because of lumen loss that I toss them, I recently tested a pretty old 400 MH bulb at half the lumens of a new one! I don't think HPS's loose as much.

[rives]

Ah, the wonders of the internet. A podium for all! Anyhow, this is from wikipedia:

All HID arc tubes deteriorate in strength over their lifetime because of various factors, such as chemical attack, thermal stress and mechanical vibration. As the lamp ages the arc tube becomes discoloured, absorbing light and getting hotter. The tube will continue to become weaker until it eventually fails, causing the breakup of the tube.

Although such failure is associated with end of life, an arc tube can fail at any time even when new, because of unseen manufacturing faults such as microscopic cracks. However, this is quite rare. Manufacturers typically "season" new lamps to check for manufacturing defects before the lamps leave the manufacturer's premises.

Since a metal-halide lamp contains gases at a significant high pressure, failure of the arc tube is inevitably a violent event. Fragments of arc tube are launched, at high velocity, in all directions, striking the outer bulb of the lamp with enough force to cause it to break. If the fixture has no secondary containment (e.g. a lens, bowl or shield) then the extremely hot pieces of debris will fall down onto people and property below the light, likely resulting in serious injury, damage, and possibly causing a major building fire if flammable material is present.

The risk of a "nonpassive failure" of an arc tube is very small. According to information gathered by the National Electrical Manufacturers Association (www.nema.org), there are approximately 40 million metal-halide systems in North America alone, and only a very few instances of nonpassive failures have occurred. Although it is not possible to predict, or eliminate the risk, of a metal-halide lamp exploding, there are several precautions that can be taken to reduce the risk:

Using only well designed lamps from reputable manufacturers and avoiding lamps of unknown origin.

Inspecting lamps before installing to check for any faults such as cracks in the tube or outer bulb.

Replacing lamps before they reach their end of life (i.e. when they have been burning for the number of hours that the manufacturer has stated as the lamp's rated life).

For continuously operating lamps, allowing a 15 minute shutdown for every 7 days of continuous operation.

Relamp fixtures as a group. Spot relamping is not recommended.

[NOTB]

i have a 600 thats 4 yrs old ,iv'e been burnin it almost constantly....been dropped a few times too with multiple scratch's...is this a bad thing? cuz if it is i didnt know., a friend that has a light meter has check'd it and it's still at full power(its a SON-T)

[poindexterous]

All I can speak from is personal experience, which tells me that HID bulbs are pretty tough, tougher than you'd think, and I'd never toss one over a scratch, only from lumen loss, but who knows maybe I'm just lucky and they blow up all the time?

[rives]

HID lamp failures are extremely rare. I was an electrician in an industrial plant that used 400 watt HPS lamps (high bay, low bay, wall pack, street lighting, etc) as a standard lamp. 400 watt metal halide lamps were used in places where accurate color perception was a requirement. This was a big plant with hundreds of light fixtures. In 20+ years, I saw only a handful of failures of the lamp envelope.

However, a metal halide lamp arc tube at operating temperature has approximately 70-90 psi inside the arc tube and runs at about 2000 degrees F. HPS lamps operate at much lower pressures and temperatures, but still significantly more than what I want blown around my grow room. Additionally, I have seen the outer envelope of metal halide lamps fail and the lamp continue operating. This is extremely hazardous because of the level of UV rays that are no longer being stopped by the outer glass.

Fractures in any type of highly-stressed material (from glass to steel) frequently develop from a surface scratch and will enlarge at an exponential rate when exposed to temperature extremes. If you want to see a good example of this, throw warm water on a cold windshield with a small crack in it (ex-wife.......).

Now with all of that being said, I personally would not take the chance on having a 2000 degree hand grenade go off in my grow room, either when it was unattended or when I was happily working away. There is a damn good chance of the debris starting a fire, and if you happen to be present.... well, 2000 degree anything isn't going to be real friendly to whatever it comes into contact with.

The following link is to a pretty interesting white paper from NEMA (National Electrical Manufacturer's Ass.) about metal halide lamp ruptures.

https://www.lightingassociates.org/i/...tal_Halide.pdf

Good thread on the subject - https://www.icmag.com/ic/showthread.php?t=218800