A 60W 200V lamp is purchased and switched on, accordingly to its specifications.
If the lamp is working perfectly, then 60J of electrical energy are transformed in 60J of luminous energy every second.
If the lamp is working perfectly, then 60J of electrical energy are transformed in 60J of luminous energy every second.
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No it's generally false. The 60W refers to the expenditure of power by the bulb. It does not refer to how much luminosity is produced. And note that Watts is a metric for power, not energy.
A good example of this is found in the LEDs. There you find 16W bulbs that expend 16 J/s power but, the packages claim, produce luminosity equivalents to a 60W incandescent bulb...something around 600-800 lumens.
While real bulbs don't work perfectly; it should be clear that the number of lumens produced per Watt can vary widely.
A good example of this is found in the LEDs. There you find 16W bulbs that expend 16 J/s power but, the packages claim, produce luminosity equivalents to a 60W incandescent bulb...something around 600-800 lumens.
While real bulbs don't work perfectly; it should be clear that the number of lumens produced per Watt can vary widely.
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the energy is transformed of course, not created or destroyed. Especially if it is an incandescent it is very inefficient, thus w/ the heat produced it leaves less energy in the form of light. As the bulb continues to heat the resistance increases further decreasing effiency.
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No, sorry, we wish all that electrical energy would go into light but most of it goes into heat loss in the hot filament. Lamps get very hot. They are great heaters but not so great radiators of light.
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They are assuming a real lamp with less than 100% efficiency. If there are 60 J/s IN, then there will be less than 60 J/s OUT.