How much does screen brightness affect battery life?

January 16, 2013 By | 2 Comments

If you have searched battery life tips on the Internet, you may have noticed every article recommended reducing backlight brightness to save power. It is true that backlight is one of the biggest power-consuming components in your laptop, but like any other battery life discussion, excessive lowering of the brightness sacrifices usability and productivity.

Therefore, it is important to know how much battery life gain you can actually get by lowering the brightness. The graph below shows how the backlight power consumption changes for different brightness settings. This data was collected on a laptop with 15-inch LED backlight panel.

Figure 1. Non-linear relationship between backlight brightness and power consumption

Although the brightness seems to change evenly (at least, for human eyes) as the setting changes, power consumption increases very rapidly as the brightness goes up. For example, power consumption difference between brightness 0 and 40 settings is only 0.5 Watt. However, the difference between brightness setting 60 and 100 is as much as 2 Watt.

What does this mean? It means, if your brightness setting is high, decreasing brightness a little bit will increase your battery life a lot. But, if your brightness is already low, further lowering the brightness may not increase the battery life as you are hoping.

Another thing you should consider is how much power is consumed by the entire laptop. If you are running heavy workload (such as game, image processing) and your laptop is consuming 45Watt, saving 2Watt power by lowering the brightness gives you only +5% of battery life. On the other hand, if you are running light workload (such as word processing, reading documents) and your laptop is consuming 10Watt, saving 2Watt power gives you +20% of battery life.

The following table summarizes how much battery life gain you can get in various situations.

Table 1. How backlight brightness affects battery life
WorkloadTotal laptop power
with lowest brightness
Battery life gain
by changing brightness
40 to 0100 to 60
Idle7 Watt7 %25 %
Light
(e.g. word processing, reading document)
10 Watt5 %18 %
Heavy
(e.g. gaming, image processing)
35 Watt1 %6 %

Summary

This is just one data point and the actual gain you will see on your laptop may vary due to various factors, such as panel size and the workloads you run. But, the following rule applies to all:

  • You can get big battery life benefit by reducing backlight brightness if your current backlight setting is very high and you are running relatively light workload.
  • If your brightness setting is already low, further lowering brightness may not give you much battery life improvement.

I hope this data will help you to find the right balance between battery life and usability.

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Comments (2)

  1. Frank

    Good, useful information. How much less power does an LED backlight consume than a CFL?

    • Luculent Systems

      For 14 to 15 inch panel, at medium brightness, LED backlight consumes 1 to 2Watts less than CFL.
      But, you probably don’t need to worry about LED/CFL difference any more because virtually all laptop PCs (even <$300 models) come with LED backlight today…

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