What is Light bulb: Definition and 142 Discussions

An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxidation. Current is supplied to the filament by terminals or wires embedded in the glass. A bulb socket provides mechanical support and electrical connections.
Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, and work equally well on either alternating current or direct current. As a result, the incandescent bulb became widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.
Incandescent bulbs are much less efficient than other types of electric lighting, converting less than 5% of the energy they use into visible light. The remaining energy is lost as heat. The luminous efficacy of a typical incandescent bulb for 120 V operation is 16 lumens per watt, compared with 60 lm/W for a compact fluorescent bulb or 150 lm/W for some white LED lamps.Some applications use the heat generated by the filament. Heat lamps are made for uses such as incubators, lava lamps, and the Easy-Bake Oven toy. Quartz tube halogen infrared heaters are used for industrial processes such as paint curing or for space heating.
Incandescent bulbs typically have short lifetimes compared with other types of lighting; around 1,000 hours for home light bulbs versus typically 10,000 hours for compact fluorescents and 20,000–30,000 hours for lighting LEDs. Incandescent bulbs can be replaced by fluorescent lamps, high-intensity discharge lamps, and light-emitting diode lamps (LED). Some areas have implemented phasing out the use of incandescent light bulbs to reduce energy consumption.

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  1. M

    Intensity of the light in the light bulb what physicist described it?

    We know that the intensity of the light in the light bulb depends on the electric current. And I want to know who was the first physicist who proved this. And if there is a possibility could you also tell me how, why, when, where he did this experiment or give me an website, but the name of...
  2. I

    Charge entering and leaving a light bulb

    Homework Statement A light bulb is rated at 30 w when operated at 120 v. How much charge enters (and leaves) the light bulb in 4.0 min? ans is 17 C Homework Equations I = P/V i = dq/dt The Attempt at a Solution I = P/V = 30/120 = 0.25A q = I*t = (0.25)(4*60) = 60 C...
  3. T

    Evaporation rate of light bulb filaments exposed to air

    I know that incandescent bulbs are filled with some inert gas to reduce the rate at which the filament decays. If the filament was to be exposed to ambient air, how long before it evaporated? How long can a mesh of light bulb filaments (or other material with as high a melting point that can be...
  4. R

    Maximum safe voltage for light bulb

    Hi, I am trying to build a conductivity meter as part of a school project (I have to measure the conductivity, among other things, of local water systems). Unfortunately, I cannot buy one for this project, as it should be home-made for these purposes. If I wanted to create a meter that...
  5. E

    Power Dissipated on light bulb

    1. A 25 ohm resistor is connected in series with a 100 W light bulb. The standard 120V/60Hz AC outlet voltage is applied to the series combination. Determine the real power dissipated on the light bulb. Assume the internal resistance of the light bulb is independent of the power dissipation...
  6. J

    How does a battery-powered light bulb work?

    In a battery-powered light bulb, what is happening in the light bulb that makes it light up? To understand what I mean by a battery-powered bulb, visit this link: http://science.howstuffworks.com/innovation/everyday-innovations/how-to-make-battery-powered-light-bulb.htm Thanks!
  7. barryj

    Why doesn't a tungsten light bulb have discrete spectral lines?

    I have been scanning a physics book. See attachment. The diagram shows that a light bulb has a continuous spectrum while the hydrogen has discrete spectral lines. Since the filament in the bulb is tungsten, why doesn't the light bulb also have discrete spectral lines?
  8. I

    Apparent magnitude of a light bulb

    Homework Statement What is the apparent magnitude of a 100W light bulb at a distance of 3 m? [Hint: Compare with the Sun to eliminate the unknown constant in the expression relating flux density to apparent magnitude.] . The solar luminosity is L \approx 4 \times 10^{26} W. . The Earth-Sun...
  9. S

    Time reversibility of electromagnetism in Incandescent light bulb

    Hi This might seem odd but I need to explain my friend on this Friend and I agreed that Classical physics is time reversible (i.e. laws remain same if time is reversed.. e.g. gravitational pull on a projectile.) only exception is II law of Thermodynamics (which talks of irreversible decrease...
  10. A

    Current through the circuit with resistor and light bulb

    Homework Statement Problem is give in the image Homework Equations V=IR The Attempt at a Solution Since its a series circuit i tried that current should be the same so it's 9/20 since there is no resistance in the bulb which is 0.45 Ω somehow the answer is 0.3Ω. why is that the...
  11. G

    How many mathematicians does it take to screw in a light bulb?

    So I just saw this joke and I thought y'all might get a kick out of it (at least those who have read one of the bourbaki books) Q: How many Bourbakists does it take to replace a lightbulb? A: Changing a lightbulb is a special case of a more general theorem concerning the maintain and repair...
  12. O

    Amount of power consumed by a non linear light bulb

    Homework Statement figure 1 shows the relation ship between voltage and current when voltage is applied o a certan light bulb. Next as shown in figure 2, the bulb os connected n series with a 12V battery and 5Ω resitor. Figure 1 http://imageshack.us/photo/my-images/585/imagnecir.png/...
  13. L

    Power Loss over 1st Light Bulb in DC Circuit w/10Ω, 12Ω, 10Ω & 12V

    A DC circuit has resistances of 10Ω, 12Ω, and 10Ω respectively. Also has 2 light bulbs with identical tungsten (resistivity = 5.6* 10^-8) filament bulbs with filament thickness of 12um and length of 1.2cm. The source is a 12V. what is the power loss over the first light bulb? I am not...
  14. Pengwuino

    I need a green light bulb like this

    So I have a hilarious idea waiting to be exploded onto the world and I need a green light bulb. I have this bulb that is a 2.5V 0.3A incandescent bulb. I'm not entirely sure I know how to determine the type of base, but I could probably grab a micrometer and some diagrams and figure it out...
  15. N

    A 25W Light Bulb Married a GE Clock/Radio

    I'm wiring a 25W Edison bulb to an old GE clock/radio. The radio is 120V/60hz 8.5W input. Basic calculation I = P/E would mean the current is 0.07A If I wire the bulb in parallel between source and the clock/radio, there's now 0.2A for the bulb branch and 0.07A for the clock/radio...
  16. H

    Light bulb uses current or resistance?

    Whoosh! Just read electricity. Resistance results in heat. The filament of bulb uses heat to light up. Keeping this in mind and the equations of power, current, voltage, resistance: °Light bulb uses current or resistance to light up and illuminate? °What's the difference between a...
  17. C

    Light bulb & photovoltaic cell & power transformer combo for FREE energy

    Does anyone think that it's possible to have a perpetual motion machine electricity generation of a combo of a light bulb shining light on photovoltaic cells that are connected to power increase transformer coils to power that light bulb? I suppose there would have to be some kind of way to...
  18. M

    Max temperature for 3.2 V incandescent light bulb

    In my physics lab, I calculated a value of 5436 deg C for the max temperature of the filament by measuring its resistance. Is it possible for a filament to reach this temperature? I'm thinking it might be since the wire is so small that it wouldn't kill the world.
  19. A

    Radiation pressure of a light bulb

    1. Homework Statement Estimate the radiation pressure due to a 100 W bulb at a distance of 8.4 cm from the center of the bulb. 2. Relevant equations Power= Work/Time W=Force(distance) Pressure = Force/Area = Poynting vector/speed of light 3. The Attempt at a Solution I found the cross...
  20. B

    Are photons from a light bulb and the sun the same for our bodies?

    Photons activate hormones in us which cause us to wake up. I'm wondering if there is a different between the photons coming from the sun and the photons coming from a light bulb? Do these both have the same effect on the body? I've put this in the classical category because of optics.
  21. N

    Would the light bulb light up from the electromagnetic wave?

    In the picture below http://www.geo.mtu.edu/rs/back/spectrum/e_mag.gif a bulb is placed on a wire parallel to the direction of the electric field. The bulb is directly on the x-axis where the two waves cross each other. 1. Would the bulb glow when the wire is parallel to the direction...
  22. R

    Best location for a light bulb filament using a concave mirror?

    Where is the best location for a light bulb filament to be placed in a spotlight, when using a concave mirror? It makes the most sense to put it at the focal point of the mirror if you want parallel light beams but are you supposed to have parallel light beams when you use a spotlight? Or do...
  23. V

    Sunlight equivalent light bulb

    If the 'average' intensity of direct sunlight on a warm summer day could be re-produced in a full spectrum light bulb, how many watts would that bulb be? I'm trying to find a bulb I can use to calibrate a photo sensor to sunlight intensity but my shop is on the base floor where there are no...
  24. K

    Calculating Resistance of a Light Bulb

    Homework Statement Hook up a round bulb to two D batteries. Measure the voltage drop across the bulb. Measure the current flowing through the bulb. Calculate the resistance of the bulb. V=2.25v; I=0.24A Homework Equations R=deltaV/I The Attempt at a Solution Is the "V" in the...
  25. Drakkith

    Solving Light Bulb Interference Issues

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  26. J

    Rms Electric Field of a light bulb

    Find the root-mean-square electric field (averaged over all frequencies) at a point in space 1 meter from a 40-watt light bulb. The emitted power: P = 40 W R = 1 m Intensity: S = P/(4\piR2) S = (c/4\pi)<E2> Erms = (<E2>)1/2 Now I will set the two equal and solve for <E2>...
  27. S

    Discharging of a capacitor through a light bulb.

    Homework Statement Which of the following statements about the discharging of a capacitor through a lightbulb are correct? a. Electrons in the wires flow away from the negative plate, toward the positive plate, reducing the charge on the plates. b. The electric field at a location inside...
  28. X

    Calculating Resistance in a Light Bulb

    Homework Statement A "90-watt" light bulb uses an average power of 90W when connected to an rms voltage of 120V . What is the resistance of the lightbulb?Homework Equations Pav=(V2rms/R) The Attempt at a Solution 90W = 120V2/R 90W/120V2 = R R = .00625\Omega
  29. K

    Find Out Which Switch Turns On Light Bulb Brain Teaser

    This is a pretty easy problem, there is a room that is enclosed and all of the walls are opaque, there is no way to know what is going on inside from the outside (you are on the outside). There are three switches outside in which one of them has a circuit that flows to the light bulb. You can...
  30. N

    Relationship between voltage and distance between light bulb and solar cell

    School experiment: Shine lamp at a solar cell, and measure the voltage using a multimeter. Independent variable is the distance between the light bulb and solar cell, dependent variable is the voltage. What is the relationship between the two? And how exactly do I prove it? What I have...
  31. C

    Compact fluorescent light bulb in microwave

    So when you watch those youtube videos and they put a compact fluorescent light bulb in the microwave and it starts to glow , but how come we get visible light from something that we are shooting microwaves at , it seems like conservation of energy does not hold . but then when i was...
  32. D

    Doubling voltage and power in a light bulb

    Homework Statement A light bulb is designed for use in a 120 V circuit. If by mistake it is plugged into a 240 V circuit, what will happen to the power of the light bulb? Explain. Homework Equations I = V/R P = VI The Attempt at a Solution Since I = V/R and the resistance of the...
  33. G

    Light bulb brightness in a circuit

    ok revision question fo me, just want to check my reasonning. which of te bulbs on the circuit of the attatched file will shine more brightly? i think p....because s and t r and q are in parrellel which is resistance 1/Rs+Rt+1/Rr+Rq where Rp is the sum of the resistance of 1/Rs+Rt+1/Rr+Rq...
  34. D

    Electric field around a light bulb

    Homework Statement What is the peak electric field 2 metres away from a 60W light bulb. Assume that the light emits light evenly in all directions (spherically uniform). Homework Equations I figure that this is to do with the poynting vector. S = \frac{1}{\mu_0}(\vec{E} \times...
  35. C

    Using DC Power to Create Electron Flow in a Tungsten Filament Light Bulb

    If i have a light bulb , and it has a tungsten filament and when i turn it on its gets hot , If i hook a lead to the filament and then put the anode away from the filament can i get electrons to flow through the vacuum , assuming this is done with DC current. If we used 2 different...
  36. 0

    How does the change in voltage affect the brightness of a light bulb?

    Homework Statement A light bulbs brightness can be measured by its power consumption. This in turn will depend on the I, V and R of the light bulb. The light bulb is rated at a power consumption of 1.0W when placed at a voltage of 6.0V. We change the battery from a 6.0V to a 3.0V one. Will...
  37. Y

    How come a light bulb does not explode?

    I have two questions actually: 1. According to Stefen's Law formula power created by an conventional tungsten bulb can be calculated and temperature of the filament is about 3500 K. I know it has low pressure gas inside a bulb but doesn't that mean sooner you switched on the bulb the pressure...
  38. L

    Equation for the power a light bulb would radiate

    Homework Statement An ordinary 150-Watt light bulb has a resistance of about 96 ohms. Suppose you were to connect a 2.0 V battery to such a light bulb. How much current would flow? Determine how much power the bulb would radiate? (probably too little for a person to detect). Use you own...
  39. W

    Refrigerator and its light bulb

    The interior lighting of the refrigerators is provided by incandescent lamps whose switches are actuated by the opening of the refrigerator door. Consider a refrigerator whose 30-W lightbulb remains on continuously as a result of a malfunction of the switch. If the refrigerator has a COP of...
  40. D

    Number of photons emitted from a light bulb entering the eye

    Homework Statement A 100W bulb emits light of a single wavelength 6000*10^-10 m. If light spreads out uniformly in space, how many photons enter your eye per second if you are at a distance 1m from the bulb and the pupil diameter is about 1mm? Homework Equations E = hc/lambda The...
  41. E

    How Can an LC Circuit Prevent Light Bulb Filament Damage at Turn-On?

    The room temperature resistance of the tungsten filament in an ordinary incandescent light bulb is about 1/15th of the hot resistance exhibited during the normal operation at 117 VAC. Therefore, when you throw the switch to turn on the light bulb there is a huge surge of current in excess of the...
  42. R

    Theoretical AC/DC Circuits: 1.5V Light Bulb & Battery

    Out of curiousity, I am wondering what happens, theoretically of course, if we place a 1.5V AC light bulb (which do not exist) onto a DC circuit with a 1.5V battery? What would happen if we connect this battery backwards on the circuit (positive to the negative terminal and vice versa). This...
  43. G

    How much power does a light bulb connected to a 120 V outlet use if it draws .5 A of?

    Homework Statement A) How much power does a light bulb connected to a 120 V outlet use if it draws .5 A of current? Show your calculations B) One kilowatt hour is a measure of energy which is equal to 3,600,000 J. How many hours would you have to leave on the light bulb from part A...
  44. I

    A Solenoid, a Moving Magnet, and a Light Bulb -- Will the Light Bulb LIght Up?

    Homework Statement "A light bulb is connected to a coil of wire. If a magnet is passed back and forth through the coil the bulb will light up. Why?"Homework Equations The Lenz Law isn't really an equation, but it states that: "The magnetic field of the induced current is in a direction to...
  45. J

    How to build an RC circuit for intermittent light bulb?

    RC Circuit -------------------------------------------------------------------------------- Hi guys, I am trying to built an RC circuit in series to light a bulb intermitently. That is on and off in a time interval. Any ideas?
  46. D

    Moving light bulb sphere of photons

    If you have a moving light bulb and an observer at rest wrt the light bulb. The observer is tiny and he is inside the light bulb. The light bulb is traveling along the x axis. The light is then turned on what will the observer see..a sphere of photons traveling outwards from the observer...
  47. C

    Can we power a light bulb with positrons?

    would we need anti-tungsten to do it.
  48. P

    Calculating Current Through a 100W Light Bulb

    Homework Statement light bulb rated 100Watts. How much current (in A) would go through the light bulb if it were plugged into the regular electrical outlet? Homework Equations P=IV The Attempt at a Solution Im not sure what the potential difference is..
  49. P

    Will an AC Light Bulb Burn Out on a DC Circuit?

    Assuming equal voltage, will it burn-out an AC light bulb if I put it on a DC circuit?
  50. N

    Please Explain when an RC Circuit Opens - Effect on a Light bulb

    Homework Statement Initially the switch is closed in the circuit shown and the light bulb is shining brightly. What happens when the switch is opened? (diagram in attached link) 1. The bulb goes out immediately. 2. The bulb gets gradually brighter. 3. The bulb gets gradually dimmer...
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