Alarm LED brightness

[cwcw]

Any ideas anyone as to why my dash Alarm LED brightens up when the car revs increase, not a major problem I agree but its niggling & I want to find the cause of the change in brightness as revs increase?

 

[jack_davey]

shouldnt really be on while you're driving, but the output of the alternator will increase slightly as the engine speed increases and thus it will get brighter