Question: What is the name of the air-tight glass enclosure in an incandescent bulb?
Answer: the envelope

Question: What is the filament made of?
Answer: tungsten wire

Question: How many conductors are present in the bulb's base?
Answer: two (or more)

Question: What prevents air or gas leaks from a light bulb?
Answer: a stem or glass mount anchored to the bulb's base

Question: What function do small wires in a light bulb's stem perform?
Answer: Small wires embedded in the stem in turn support the filament and its lead wires

Question: What is the powdery substance in coated glass light bulbs?
Answer: kaolin

Question: How is kaolin placed inside a light bulb?
Answer: blown in and electrostatically deposited

Question: What is the effect of a kaolin coating on the light cast?
Answer: a more gentle and evenly distributed light

Question: How are Christmas colored light bulbs created?
Answer: by coloring the glass with a dopant

Question: How does kaolin create a more gentle light?
Answer: It diffuses the light emitted from the filament

Question: What is the name for a base with one or more contacts at the tip and one at the shell?
Answer: screw base

Question: What is the name for a lamp base with one or more contacts on the base and a shell used as a contact or used only as a mechanical support?
Answer: bayonet base

Question: What is the purpose of contacts in the lamp socket?
Answer: allow the electric current to pass through the base to the filament

Question: What is the range of power ratings for incandescent bulbs?
Answer: 0.1 watt to about 10,000 watts

Question: Which types of lamps use screw terminals for connection to wires?
Answer: automotive and special purpose lamps

Question: What is a potential problem with the use of gas in a light bulb?
Answer: introduces heat losses (and therefore efficiency loss)

Question: What are the ideal chemical properties for the gas in a light bulb?
Answer: chemical inertness and high atomic or molecular weight

Question: What is the purpose of the gas in a light bulb?
Answer: to prevent evaporation of the filament, without introducing significant heat losses

Question: How do gases prevent evaporation of the filament?
Answer: The presence of gas molecules knocks the liberated tungsten atoms back to the filament

Question: What type of machine manufactures glass light bulbs.
Answer: ribbon machine

Question: How many bulbs does the average ribbon machine produce per hour?
Answer: 50,000

Question: How is the filament attached to the bulb?
Answer: assembled on a glass stem, which is fused to the bulb

Question: How is the evacuation tube sealed?
Answer: by a flame

Question: What blows the glass bulbs into their characteristic shape?
Answer: precisely aligned air nozzles

Question: What material were the first light bulb filaments made from?
Answer: carbon

Question: What was the primary problem with early carbon filaments?
Answer: as they got hotter, their electrical resistance decreased

Question: What were the positive effects of the flashing process?
Answer: improved the uniformity and strength of filaments as well as their efficiency

Question: What properties of graphite improved the filament?
Answer: further strengthened and smoothed the filament

Question: What are the effects of giving the filament a positive temperature coefficient?
Answer: helped stabilize the lamp's power consumption, temperature and light output against minor variations in supply voltage

Question: What company invented the tantalum light filament?
Answer: Siemens

Question: In what year was the tantalum light filament invented?
Answer: 1902

Question: What were the major advantages of the tantalum light filament?
Answer: These lamps were more efficient than even graphitized carbon filaments and could operate at higher temperatures.

Question: Who purchased the rights to the tantalum light filament from Siemens?
Answer: General Electric

Question: When did GE cease production of the tantalum light filament?
Answer: 1913

Question: What was the problem with manufacturing the tungsten filament?
Answer: Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires.

Question: Who developed the ductile form of tungsten?
Answer: William D. Coolidge

Question: When was the ductile form of tungsten invented?
Answer: 1910

Question: When was the tungsten filament introduced?
Answer: 1906

Question: What other materials were combined with tungsten?
Answer: potassium, silicon, and aluminium oxides

Question: How long is a typical uncoiled tungsten filament for a 60-watt bulb?
Answer: 22.8 inches

Question: What is the advantage of a coiled-coil filament over a straight filament?
Answer: The coiled-coil filament evaporates more slowly

Question: What positive effects does a slower-evaporating filament enable?
Answer: more efficient light source

Question: What is the typical diameter of the filament on a 60-watt bulb?
Answer: 0.0018 inches

Question: What is the negative effect of "hot spots" forming on the filament?
Answer: a variation of diameter of only 1% will cause a 25% reduction in service life

Question: Who discovered that inert gas could slow evaporation?
Answer: Irving Langmuir

Question: Which gases are typically used in a light bulb?
Answer: argon and some nitrogen, or sometimes krypton

Question: Which type of alloys can decrease "stairstep" irregularities in light bulb filaments?
Answer: alloys of tungsten and rhenium

Question: Why does inert gas reduce efficiency?
Answer: conducts heat from the filament, thereby cooling the filament

Question: What affects the thermal conductivity of a gas?
Answer: molecular weight of the gas and the cross sectional area of the gas molecules

Question: How does the molecular weight of a gas relate to thermal conductivity?
Answer: Higher molecular weight gasses have lower thermal conductivity

Question: Why is xenon gas not more widely used?
Answer: more expensive, so its use is limited to smaller lamps

Question: What is the advantage of using inert gas in a light bulb?
Answer: reduces filament evaporation

Question: What determines how fast a tungsten filament evaporates?
Answer: hotter, more-efficient filaments evaporate faster

Question: What is the typical goal for the life of a tungsten filament bulb?
Answer: several hundred to 2,000 hours

Question: Which types of lamps may have particularly short lives?
Answer: Theatrical, photographic, and projection lamps

Question: What is the typical tradeoff in light bulb design?
Answer: efficiency and longevity

Question: What darkens a conventional bulb over its lifetime?
Answer: the evaporated tungsten eventually condenses on the inner surface of the glass envelope

Question: What is the IEC guideline for an unacceptable level of light loss?
Answer: An incandescent lamp that gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory

Question: What are the primary causes of light loss?
Answer: Light loss is due to filament evaporation and bulb blackening

Question: Where in the bulb is evaporated tungsten deposited when inert gas is used?
Answer: on the uppermost part of the envelope

Question: Where in the bulb is evaporated tungsten deposited when a vacuum is used?
Answer: across the entire surface of the envelope

Question: How does water vapor inside a light bulb affect lamp darkening?
Answer: significantly increase darkening

Question: Why does water increase lamp darkening?
Answer: The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp.

Question: What is an example of a substance that is added to light bulbs to reduce this effect?
Answer: zirconium

Question: How much water is necessary to result in this darkening affect?
Answer: The equivalent of a drop of water distributed over 500,000 lamps