Will a resistor in series extend battery life?

If a current limiting resistor is placed in series in a simple led circuit on a 3v watch battery for example, will the led remain illuminated (but dimmer) for a longer period of time versus no resistor at all? It would seem so becuse the resistor limits current but isn't that additional power simply wasted as heat energy in the resistor, essentially draining the battery at the same rate?

Apologies if this has already been asked but I've seen somewhat contradicting answers to this question elsewhere on the internet.

The battery will last longer with the resistor because the total current and total power consumption is lower.

You're correct that some energy is wasted in the resistor.

You should always have a current-limiting resistor because LEDs are non-linear. Their resistance drops when voltage increases and you can get excess current. With a watch battery the LED will probably survive but you are relying on the internal battery resistance to limit the current and the battery voltage will drop to the LEDs forward operating voltage.

High power LEDs are driven by switchmode constant-current drivers so there is no power lost across the resistor. With regular LEDs the power loss in a resistor is usually not significant, but in some battery operated applications some additional circuitry may be worth it.

However... Switching power supplies consume more power just to operate so it usually doesn't make sense in low power applications. They are very efficient at higher power.

moses1592:
but isn't that additional power simply wasted as heat energy in the resistor,

There is a trade off between power wasted in the resistor and power left in the battery (see below).

moses1592:
essentially draining the battery at the same rate?

The rate at which the battery is drained is the charge/current. Adding a resistor will limit the current and therefore the rate at which the battery is drained.

moses1592:
Apologies if this has already been asked but I've seen somewhat contradicting answers to this question elsewhere on the internet.

That is because the answer to the question depends on the value of the resistor.

If the resistor value is high the current will be lower therefore draining the battery slower. But at the same time a high value resistor will have a high voltage drop. As the battery voltage drops this voltage drop across the resistor will prohibit the LED from emitting light before the battery is empty.

On the other side a lower value resistor will make the LED shine brighter at the beginning draining the battery faster but will allow the LED to shine when the battery voltage has dropped to a lower level.

You will get less total light but for longer with a resistor.
However sense of intensity is logarithmic: a large reduction of current (i.e. from 20 to 2 mA) causes not so large reduction in apparent intensity but in a huge increase of battery life.

And of course, using PWM to dim may be more efficient. :sunglasses:

Thank you for the replies, this is exactly what I wanted to know!