What do you mean by a Wattage of an incandescent bulb?

Question

How do I interpret the wattage of a bulb. For example when it is said that the bulb is rated for 60 W , what does that mean?

You may want to "accept" the higher rated answer. – Rev Mar 23 '19 at 18:58 — Rev, Mar 23 '19 at 18:58

score 10 · Accepted Answer · 2013-04-19T08:50:01.903

Watt (\$W\$) is the unit of Power (\$P\$). There is an equation that says:

$$E = P \cdot t$$

You can see that Energy (\$E\$) equals Power (\$P\$) times time (\$t\$). There is a linear relationship between Energy and Power, so the higher the Power (wattage) of a device, the more energy it consumes.

The same formula, in a different form:

$$E=P \cdot t \rightarrow P=\frac{E}{t} \rightarrow W=\frac{J}{s}$$

One Watt means one Joule (\$J\$) per second (\$s\$) is being consumed. 60W means 60J/s is being consumed by the bulb.

score 8 · Answer 2 · answered Apr 19 '13 at 15:51

Typical bulbs specify a wattage and a voltage. The figures together mean that when the indicated voltage is applied in free air in a room-temperature environment, the bulb's temperature and resistance will find an equilibrium state where the bulb consumes the indicated amount of electrical power (giving it off as some combination of conducted heat and radiated energy).

If a different voltage is applied to a bulb, the filament will reach a different equilibrium temperature and may, as a consequence, have a different resistance. If the resistance were constant, power would be proportional to the square of voltage, so a 10% reduction in voltage would represent about a 19% reduction in power. In practice, reducing voltage by 10% will reduce power by significantly less than 19%, but the reduction in visible light will be significantly greater than 19%. Although operating a bulb at at a lower voltage will greatly reduce efficiency, it will greatly improve longevity. There's a light bulb in San Francisco which doesn't burn very bright, but has been going almost continuously for over 100 years.

score 4 · Answer 3 · answered Apr 19 '13 at 08:44

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if you have 60W bulb, and your mains supply 220V then that means the bulb is drawing 60/220 = 0.273A of current.

So there must also be a voltage rating along with the wattage to be meaning full. Also, more is the wattage, more energy it consumes.

answered Apr 19 '13 at 08:44

Arjob Mukherjee

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"So there must also be a voltage rating along with the wattage to be meaning full." that is not true. See my answer, I don't talk about voltage, yet I do extract useful information from the 60W specification. – Apr 19 '13 at 13:22
@CamilStaps Yes, you are right. Thanks for pointing the mistake! – Arjob Mukherjee Apr 20 '13 at 17:06

SAYAN · Answer 4 · 2019-03-23T14:27:23.427

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power is the rate at which energy is being used, the unit for energy is joules, as we use the term megabyte/second to denote the transfer rate at which data is being sent or received, similarly power=amount of energy used/second, in a similar way by 1W we mean in each single second, 1 joules of energy is being used (transformed into another energy or transferring whatever). now a bulb of power rating 60W, 220v means that when the bulb is connected to a 220V mains, it will consume 60 joules of energy in each second, some of this 60 joule is converted into light and some of the 60 joules of energy is converted into heat. however, if you want to put it in another way, for an electronic/electrical equipment, WATTS=VOLTS x AMPERES.

edited Mar 23 '19 at 14:27

answered Mar 23 '19 at 13:16

SAYAN

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We don't expect every post to be perfect, but posts with correct spelling, punctuation, and grammar are easier to read. They also tend to get read and upvoted more frequently. Remember, you can always go back at any time and edit your post to improve it. See Write to the best of your ability on the site's help pages. Your last sentence "1 watt=VOLTAGE CURRENT*" is not correct. P = VI or watts = volts x amperes would be correct. – Transistor Mar 23 '19 at 13:20
OOOPPPS, Fixed. – SAYAN Mar 23 '19 at 14:20

score 0 · Answer 5 · answered Nov 11 '19 at 12:13

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If the power rating of bulb is given 60W Nd we know household electricity is at 220V Means this bulb is having resistance R = 220^2/60 = 806.667 ohm Nd it's drawing a current of I = 60/220 = 0.2727 A

answered Nov 11 '19 at 12:13

Vikas Sharma

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What does "60W Nd" mean? 220 V is not universal. 120, 220, 230 and 240 V are the common standards. The resistance is the resistance at operating temperature. Given that 60 W is probably +/- 20% there is no point in calculating resistance to 6 significant digits. Welcome to EE.SE. – Transistor Nov 11 '19 at 12:41

What do you mean by a Wattage of an incandescent bulb?

5 Answers5