For a project I'm considering a 4-digit 7 segment display (4 banks with 7 diodes each).
Given typical specifications (e.g. If=20mA max @ Vf=2V per segment) I would expect light intensity for a single segment to be reasonable at around 10mA steady current. What should I then expect in terms of light intensity when duty-cycle drops to 1/4?
Is the relationship roughly linear so that in order to maintain the same perceived brightness - I will need to feed each segment with 40mA?
What should I then expect in terms of light intensity when duty-cycle drops to 1/4?
The light intensity will drop by 1/4.
However, they eyes response is logarithmic so it will not look 1/4 the brightness. But it will look as bright as 1/4 DC current going through it. So 40mA sounds reasonable if you want the same brightness as 10mA.
Thanks!
Do you also happen to know if this switching of higher current will have a negative impact on life expectancy for the segments - or is it again about the same?
If you look at the data sheet for the LED there will be pulse current rating as well as a continuous current rating. Stay below that and you will be OK.