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Typical Bulb Failures

bulb failures & checking for unused bulbs


Before installing bulb, check bulb carefully for damage. Then, with a towel lightly dampened with window glass cleaner or rubbing alcohol; wipe all fingerprints, dust and impurities from bulb's glass surface. Let dry thoroughly before installing. DO NOT TOUCH GLASS with fingers after cleaning. Handle glass with clean dry towel or cotton glove.

Also, make sure bulb is warmed up to room temperature before installing.

When used, bulb may shatter or explode if very cold, or if it contains fingerprint oils or moisture. This is especially concern for Halogen and high wattage/temperature bulbs.


Normal Life Failures:
Normal life failure: Lamp has obviously served normal rated average life. Note the blackening on top of reflector and top of bulb. (If lamp has an opaque top, look under the top for signs of blackening in an otherwise "clean" looking lamp.)Normal life failure: Lamp was designed to burn horizontally and the telltale blackening is on the side of the envelope indicating a normal life.Normal life failure: This shows another effect that can result from normal burning life - a blackened bridge and/or support.Normal life failure: This lamp has blistered after it was used for a number of hours. Glass bridge (and under opaque top) will also be blackened, as previous examples, indicating usage.



Early Failures and Damaged Bulbs:
Cracked Glass: Internal reflector support flexed during rough handling, smacking inside of glass, cracking outer glass envelope. Instead, sometimes reflector will crack or chip, in which the bulb may still live out a normal life.Leaker: A tiny leak in glass envelope has allowed air to enter the bulb. Milky, cloudy appearance identifies this condition.Early failure: Lamp appears perfect except for broken filament; obviously has not been burned any length of time, if at all. Gently tapping bulb with fingernail will help locate bad filament.Broken Support: Check all supports, welds and solder joints for structural damage. Feel for rattles and vibrations while gently shaking and lightly tapping glass with fingernail.
Floating Debris: Turn bulb sideways and lightly tap with fingernail. Loose glass floating inside probably was caused by rough handling. Look to see the shape of the glass pieces. If they are flat flakes or thin shards they probably came from the reflector edge and bulb should be okay. BUT, if glass pieces are "chunky" they probably originated around electrical contacts or structural supports and if airtight seals are damaged; oxygen can enter shortening bulbs life. Use this test to also check for "floating" broken internal components such as supports, insulators, wires, filaments, and foreign debris which may not have been cleaned out before bulb was assembled. Depending on what's floating and as long as air doesn't enter, bulb may still live out a normal life.


Fingerprint: Oils from fingerprints and other contaminations on quartz bulbs causes divitrification chemical reaction when bulb is heated. Quartz glass crystallizes becoming brittle causing premature glass failure (bulb could explode.) Remove all contamination from glass before installing.


Oxidized Filament: Filaments should be bright and shiny. Both of these unused bulbs came from the same manufacturers lot and are about 30 years old. A filament is in perfect condition, but filament B has oxidized and gone bad. Over time, the wire passing through the glass envelope on the left has oxidized, and oxygen has slowly crept along the wire into the bulb contaminating the bulb. Oxygen leaks such as this are manufacturers quality control problems. Oxidized filaments will be dark (not bright and shiny) or beautiful deep crystalline colors. If bulb B was turned on, filament would quickly burn out. Although example B is an extreme example of oxygen leak / contamination, any degree of oxidation of the filament is the sign of a bad bulb. Oxidation on metal parts OTHER than the filament do not indicate a bad bulb, as this oxidation often occurred before the bulb was assembled. Also, some bulbs have parts painted with a highly reactive type of "getter" which is designed to absorb (by oxidation) any stray oxygen rendering it harmless.


checking frosted bulbs: If frost is etched on outside glass, room temperature frosted glass will turn clear (invisible) by putting drops of water on glass allowing visual inspection of filament and supports. Remove water thoroughly before installing dry bulb.




Checking for Unused Bulbs:
At the factory, each bulb is turned on for testing anywhere from seconds to minutes (depending on the bulb type) so some minimal signs of usage are present with every bulb. Some bulb designs have filtered glass (like UV coating) which may appear slightly tinted (not blackish).
White Paper Test: Put sheet of bright white paper behind bulb. Bulb is used (not new) if much sooting (dark tinting) exists inside glass, reflector or supports. Be sure to check under opaque top.

On some bulbs a small amount of soot might exist from factory as by product of burning off the getter (oxygen removal.)

Check filament isn't broken.
Sooting: Blackening of bridge and/or support indicate bulb is used. Green arrow shows normal manufacturing discoloration and isn't an indication of usage.Blistered Glass: Any signs of bubbling or blistering of glass is sure sign of a used bulb.Heat discolorations: Any yellowing or browning on light colored ceramic insulators indicates bulb is used.
New Filament is shiny and smooth regardless of shape. A new filament has a dull even shine.Used Filament surface becomes pitted and irregular as it's consumed by use, then eventually burns out normally. As filament depletes, it gets thinner and more fragile so be extra careful of vibration and rough handling. If filament appears glittery or sparkles then bulb is not new.
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