What is Lightbulb: Definition and 69 Discussions

An electric light is a device that produces visible light from electric power. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and nighttime activities. In technical usage, a replaceable component that produces light from electricity is called a lamp. Lamps are commonly called light bulbs; for example, the incandescent light bulb. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the socket of a light fixture. The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap.
The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, such as fluorescent lamps, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor.
Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. English chemist Humphry Davy developed the first incandescent light in 1802, followed by the first practical electric arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. Efforts by Joseph Swan and Thomas Edison
led to commercial incandescent light bulbs becoming widely available in the 1880s, and by the early twentieth century these had completely replaced arc lamps.The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to many applications. Most modern electric lighting is powered by centrally generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems. Battery-powered light is often reserved for when and where stationary lights fail, often in the form of flashlights or electric lanterns, as well as in vehicles.

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  1. C

    Why a 20 Ohm lightbulb won't light up in a closed circuit?

    When using the voltmeter and ammeter to investigate the circuit, it was found that the batter had a current of 0.67 A, the two 30 Ω bulbs had a current of 0.17 A, and the two 10 Ω bulbs had a current of 0.50 A. In terms of voltage, each bulb had a voltage of 5 V. When the switch was closed, the...
  2. O

    Electrical How do I.... Change a lightbulb?

    I attached a picture. I bought my house in February and one room has these lights inset into the ceiling. The whole fixture can kind of jiggle around with the light in it. How am I supposed to remove the bulb? It doesn't obviously unscrew or anything. Do I need to remove the whole fixture?
  3. e101101

    How do I modify plane waves to represent the EM field of a lightbulb?

    I don't know where to start for part (c), I've managed to get (a) and (b). Can someone simply guide me, I think I'm having trouble understanding what the teacher means by just having an x dependance... Does this mean I only work with the x components of the magnetic field and the electric...
  4. O

    What does a lightbulb prefer? Volts or Amps?

    Lightbulbs are rated in watts. Watts = energy/time = volts*current Does it matter if you have a very low voltage source with a very high current or a very high voltage with a very low current? If the voltage and current multiplied meets the power rating, what should it matter what proportion...
  5. S

    Lightbulb and mini hydro generator

    I am using a 1.5 V incandescent light bulb. I know that if I connect a 9V battery to it or any higher voltage, it will burn it due to the large current flowing through it (Ohm's law if V goes up then the current goes up as well assuming constant R). Now I a have a 12 V mini hydro generator...
  6. nmsurobert

    Power relation to lightbulb wattage

    Power is measured in watts and lightbulbs are rated in watts. P = W/t and W = Fd What is being displaced? electrical current?
  7. A

    Final Temperature of a Lightbulb filament

    Homework Statement When an incandescent light bulb is switched on, it can take a few moments for the filament to fully heat up and reach its equilibrium temperature. Assume the filament of a given light bulb is made of Tungsten, and also assume the potential difference across the filament is...
  8. S

    Analyzing Brightness in Series Lightbulb Circuits

    Hi Two lightbulbs in series, one with 50W one with 100W which is brighter. I have two different solutions and can't see my error. Using PR=V^2 and I^2=P/V 50/√50R1=100/√100R2 with the same current and R2=2R1. Using PR=V^2 and the same voltage across both bulbs yields 50R1=100R2 or R1=2R2. Which...
  9. clamatoman

    How many Photons per second are entering the pupil?

    Homework Statement (a)Estimate the number of photons per second emitted by a 100-W lightbulb, assuming a photon wavelength of 550nm.(b) A person can just see this bulb for a distance of 800m, with the pupil dilated to 7.5mm. How many photons per second are entering the pupil? Homework...
  10. RoboNerd

    Question on lightbulb brightness in circuit analysis

    Homework Statement Homework Equations I know that power of a lightbulb/resister is I^2 * R The Attempt at a Solution OK. Here's my attempt: Let's consider the situation where we do not close the lightbulb and assume that the wires and switch are ideal because they have no resistance. I...
  11. RoboNerd

    Lightbulbs and a battery circuit

    Homework Statement Homework Equations no equations The Attempt at a Solution I know that we will have an equal current flowing through bulbs 1 and 2 when we connect them in parallel in accordance with kirchhoffs voltage law which says that the voltage drops around both paths must be equal...
  12. J

    Recharging a battery when Lightbulb and TV are in parallel

    Homework Statement In a household, the wife reads a book that uses a light bulb that has a resistance of 100Ω and is connected to a 100 V line while the husband watches a TV that draws 100 W of power. They do these actives for 200 mins. Power comes from a wind generator that charges batteries...
  13. Firye Stanly

    Electrical power of a lightbulb

    Homework Statement Two identical light bulbs are connected to the ends of the battery. In the first case they are connected in series and in the second they are connected in parallel mode. What is the ratio of the electrical power of light bulbs connected as mentioned? Homework Equations...
  14. N

    Understanding the Relationship Between Resistance and Brightness in Lightbulbs

    The light in a lightbulb is the result of an increase in temperature. This increase is created by both a highter elektrical resistance in the wire and a highter elektric current. But a higher resistance results in a lower elektric current (I) (I=V/R), so it is both increasing and decreasing the...
  15. R

    Power consumption costs for a malfunctioning lightbulb

    Homework Statement Consider a refrigerator whose 40-W light bulb remains on continuously as a result of a malfunctioning of the switch inside the refrigerator. The refrigerator has a coefficient of performance (COP) of 1.3 and the cost of electricity is estimated to be 10 cents per kWh...
  16. Y

    Power consumed by lightbulb

    Homework Statement Figure 1 shows the relationship between voltage and current when voltage is applied to a certain light bulb. Next, as shown in Figure 2, the bulb is connected in series with a 12-V battery and a 5 ohm resistor...
  17. C

    Burnout of 6300 Lumen Light Bulb: Why?

    So I purchsaed this 6300 lumen light bulb, clear white glass, with a tugsten fillament. I have this small desk lamp that used to have some 30 or 60 watt light bulb installed. I replaced that with the more powerful one, but... why did the more powerful one burn out? One day, it just burned out...
  18. Svein

    Lightbulb Jokes - How Many Does it Take?

    Q: How many science fiction writers does it take to change a lightbulb? A: Two, but it's actually the same person doing it. He went back in time and met himself in the doorway and then the first one sat on the other one's shoulder so that they were able to reach it. Then a major time paradox...
  19. TheAxolotl

    How is the vacuum in a light bulb sealed?

    I understand that one would use a vacuum pump to evacuate a light bulb, but once a vacuum is created, how is the bulb sealed without air coming in?
  20. TravvyM

    How long can the battery power the lightbulb?

    Homework Statement A 2.9 V battery rated at 695.5 A(h) has been powering the same light bulb for 44.2 hours. The total resistance in the circuit has averaged out to be 5.3 Ohms. The light bulb has unexpectedly burned out, and was replaced with a new one. The total resistance in the circuit...
  21. MidgetDwarf

    What is the Gauge Pressure Inside a Hot Gas-Filled Incandescent Light Bulb?

    Homework Statement Suppose a gas-filled incandescent light bulb is manufactured so that the gas inside the bulb is at atmospheric pressure when the bulb has a temperature of 20.0 °C. Find the gauge pressure inside such a bulb when it is hot, assuming its average hot temperature is 65.0 °C...
  22. skepticwulf

    How Does a Lightbulb's Resistance Impact Its Power Consumption?

    Homework Statement A 100-W, 120-V lightbulb has a resistance of 12 ohm when cold (20°C) and 140 ohm when on (hot). Calculate its power consumption (a) at the instant it is turned on, and (b) after a few moments when it is hot. Homework Equations P=IV, P=I^'R, P=V^2/R The Attempt at a Solution...
  23. 4

    Current through a lightbulb after flowing through transistor

    Homework Statement Consider a 2N3904 NPN transistor in a circuit. Treat the lightbulb as a 100 ohm resistor. For different values of R, what is the current through the lightbulb? Enter two digits rounded to the nearest 0.1 amps. If R=500 ohms, the current through the lightbulb is: If R=5...
  24. K

    Photons per second from lightbulb

    Homework Statement [/B] If 5 percent of the power of a 100 W bulb is radiated in the visible spectrum, how many visible photons are radiated per second? Homework Equations E=hf=hc/λ The Attempt at a Solution I know how to solve this, I just wanted to make sure. I will take 5 W or J/s as the...
  25. minimario

    Why Won't the Lightbulb Light Up?

    Homework Statement Will the light bulb light up? Homework Equations N/A The Attempt at a Solution Why won't it light up? I see a path from the - to the +!
  26. P

    Lightbulb brightness in a circuit

    Homework Statement The circuit has identical light bulbs. A fourth identical light bulb is added to the circuit. How does the brightness of the original light bulbs change? a)All of them get dimmer b)X,Z get dimmer, Y brighter c)X,Z brighter, Y dimmer d)X,Y dimmer, Z brighter e)X,Y brighter, Z...
  27. N

    Lightbulb I/V curve question

    The question I've been given this question by a teacher and I'm clueless as to what b) and c) are. Could you please help? I would really appreciate it. The prize is a place to see a lecture on quantum simulation at our local University. Thank you :)
  28. robotpie3000

    Improving the Efficiency of Light Bulbs: Possible Solutions?

    I just finished an experiment on blackbody radiation, and one of the post lab questions asked me on the possible ways in which a light bulb can be made more efficient such that the majority of the light it produces falls in the visible spectrum. After some quick research I think one of the...
  29. S

    Why doesn't my lightbulb explode?

    I hope you are having an awesome day. Can you tell me why this is? I put twenty light bulbs (rated for 100 watts, 120 volts) in series in my room. They light up. It's real bright in here. Now I unplug nineteen of them. Why isn't the remaining either 20 times brighter or just explode. In...
  30. E

    Melting Lightbulb Filaments: What Voltage is Needed?

    Does anyone know an approximate voltage needed to melt the filament of a typical 120V/60W incandescent bulb? I'm doing a research project and I've calculated 211V. However, I don't have a power supply capable of delivering it - yet. So for now I can't test my theory. and I haven't had...
  31. M

    Efficiency of a Light Bulb: Calculating Energy Transfer

    Homework Statement "A light bulb is 85% efficient. If it is supplied with 60J of electrical energy, how much of this energy is transferred to its surroundings as light energy? The attempt at a solution So I calculated that 85% of 60 is 51J, however I don't know if being "efficient"...
  32. M

    Diffraction Grating And Lightbulb

    An incandescent lightbulb produces incoherent light. But on Wikipedia, for instance, there is a picture of it producing a rainbow diffraction pattern on the diffraction grating page. But since the bulb is putting out incoherent light, it should be intensities rather than fields that add...
  33. J

    How do I calculate the power output of the lightbulb?

    Homework Statement How do I find the answer for part C? 3) A battery with an Emf of 12 volts is hooked up to a 125 ohm resistor and an ammeter. The ammeter measures a current of 75 mA. a) Calculate the internal resistance of the battery and the actual voltage across the battery. b) Calculate...
  34. F

    Need confirmation on lightbulb experiment

    I was piddling with my meter and graphing calculator and came up with this equation y= .08x+.14 This equation uses the number of batteries for X, and the Amp draw through a light bulb for Y. The results are theoretical past 4 batteries. The batteries were 1.29 v when the experiment began...
  35. A

    CFL and lightbulb temperatures

    A CFL can be classified as "5000 K", but (correct me if I'm wrong) the gases inside the tube do NOT get anywhere near that hot. Which brings up my first question: How hot does a CFL get? Since the spectrum is not a blackbody, it's not easy to tell just by looking at the emission spectra. I...
  36. F

    Experimental results for current/power surge in a lightbulb

    Hello everyone, I have been working on my extended essay (IB) in physics these past few months, and my topic is the current surge that occurs when a light bulb is first turned on, due to temperature. I have finished all the math/theoretical part for this, and long story short, as I expected...
  37. S

    Resistors in Series with a lightbulb

    Homework Statement A lightbulb marked "75W at 120V" is at one end of a long extension cord in which each of the two conductors has a resistance of 0.800Ω. The other end of the extension cord is plugged into a 120V outlet. Find the actual power of the bulb. Homework Equations P = V^2/ R...
  38. S

    Inductor lightbulb circuit.

    I cannot seem to solve this problem: A typical "light dimmer" used to dim the stage lights in a theater consists of a variable inductor L (whose inductance is adjustable between zero and Lmax) connected in series with the lightbulb B as shown in Figure 31-36. The electrical supply is 240 V...
  39. S

    Power Dissipated by a Lightbulb

    1. The electric power P is dissipated by a light bulb of resistance R is P=v^2/R, where V represents the line voltage. During a brownout, the line voltage is 10.0% less than its normal value. How much power is drawn by a light bulb during the brownout if it normally draws 100.0 W (watts)? Assume...
  40. B

    Resistance for a lightbulb circuit

    So I've made a circuit that lights up a light bulb whenever it's dark. I did this using a photoresistor and it is working. However, I have a relay switch with a 9V battery and a 7.2V lightbulb. When it was supposed to turn on, it lasted a couple of minutes and the battery is now dead. Should I...
  41. J

    Brightness of lightbulb concept questions

    So I googled and found out that brightness of a lightbulb is directly related to current, but for some reason it doesn't match the concept I have in my head. I know that a lightbulb gets brighter as it gets hotter (like any kind of metal) So for a lightbulb to get brighter, it needs more...
  42. O

    How far from the lightbulb can you stand to see it? photon problem

    Homework Statement http://www.screencast.com/users/trinhn812/folders/Jing/media/23298f1b-2ef4-4cdf-8b7a-58c9be07335a Homework Equations E=hf The Attempt at a Solution I'm not even sure how to get the distance for this problem.
  43. A

    Find the energy given from a lightbulb

    Homework Statement You have two light bulbs: Bulb A is rated at 25 Watts and Bulb B is rated at 100 Watts. You plug it into a standard light socket that provides a voltage difference of 120 volts. Which light bulb will use more energy during the same period of time? How many more? Bulb A = 25...
  44. T

    Why Does a Light Bulb's Resistor Burn Out When Directly Connected to an Outlet?

    I was with my electrician friend the other day, and we stuck two copper wires into each of the holes of a regular 120V outlet then smashed a 100W light bulb and took the resistor (small coiled looking thing) out of it and set it on a piece of wood and touched the copper wires to each end of the...
  45. J

    Lightbulb Brightness Homework: Series & Parallel Circuits

    Homework Statement Two light bulbs of resistance R1=10 ohms and R2 = 15ohms are connected in series with a 25V battery. Which bulb glows more brightly? Now the bulbs are connected in parallel with the battery. Which bulb now glows more brightly? Homework Equations V=IR The...
  46. N

    Does the lightbulb burn? (Faraday)

    Apologies for the atrocious attempt at a drawing: So my professor said that if you close the switch, the upper lightbulb (n° 2) will go out. How exactly do you know this? Well of course, if you replace the changing magnetic field that is inducing an emf with a battery somewhere close to...
  47. T

    Absolute Magnitude of Lightbulb

    Homework Statement By comparing with the luminosity of the Sun, calculate the absolute magnitude of a 60W lightbulb. [THe absolute magnitude of the Sun is +4.75; you may ignore colour differences] Homework Equations m-M=5log(d/10pc) f = \frac{L}{4\pi d^{2}} m1 - m2 = -2.5long(f1 / f2) The...
  48. F

    Lightbulb Differences: Investigating Unusual Outcomes

    I recently ran into the situation where one of my lamps lightbulb burned out. So I changed the bulb. I left home for a second and when I came back, the bulb wasnt burning anymore. So I started to investigate it. Turns out the new bulb didnt burn out. Everything seems to be ok with it, but then...
  49. 1

    Lightbulb Brightness in a circuit.

    Homework Statement Rank the lightbulbs in order of brighness. http://img641.imageshack.us/img641/5871/lightbulb.png Homework Equations All lightbulbs are identical. The Attempt at a Solution A is brightest, then B=C, then D=E A>B=C>D=E B and C are the same...
  50. M

    How Many Amps flow through the lightbulb

    http://img257.imageshack.us/img257/7161/physics.png I only have one more chance at this problem and I can't understand why it isn't 1. I assumed that power in = power out and power = current x voltage. If the voltage remains constant, wouldn't the current as well? "In the circuit shown...