determine how long led will stay on w/ bettery

S

SklettTheNewb

Guest
I would like to calculate how long an LED will stay lit given a
specific power source. I need to know what the smallest battery I can
use in a project and still get n hours of operation.

For example:
if I have a typical LED and a 1.4v battery 130mah (hearing aid
battery), how long will it stay lit to the point where you can't
visually determine it's dimming..

What is the formula?

Also, does a flashing LED consume a non-linear amount of power? In
other words, if I had an led that was on 50% of the time, could I
double the duration value from the above said formula?

As you can tell, I don't really know anything. I just have an idea for
something and am trying to determine how feasible it is...

Thanks for any help!
Steve
 
great, thank you for the response.
So with that calculation and a 1.5v, 140mAh battery and a 1.5v, 20mA
LED, I would be looking at roughly 70 hours of constant operation.

That is pretty good ;)

Thanks again!
 
thanks for the reply!

I understand what you're saying about circuit draw and duration. for
my needs I would just need a quick "tick" on, then 1500 milliseconds
off.

I found these circuits using 555 chip
http://home.cogeco.ca/~rpaisley4/LM555.html#4

I guess I will need to learn how to use a multimeter so that I can
determine how much a circuit like this will draw, but it looks like I
can set the frequency to what I want using of these circuits.

If there is a more effecient way, I would like to know about it. I
don't intend to develop the circuit myself, I just need to determine if
this project makes sense before I think about speaking to a pro and
possibly putting out $$, you know?

I appreciate your help so far.
Steve
 
god, the internet is great ;)
http://www.discovercircuits.com/PDF-FILES/3vledfs1.pdf
 
yes I did, typo ;(

I was thinking I could boost it up w/ transistors, at least things I
have read in the last hour make me think that is possible.
 
Hi Ray,

I'm not trying to light so much as indicate or get attention. This
device will need to be roughly the diameter of a sharpie and about 1/2
as long, so dueling AAA are out, plus they are relatively heavy for
what I envision. It really seems like series of tradeoffs thus far, I
can utilize more power up front and have a cost/weight/size hit or I
can have "booster" circuits(if I can call them that...) at the cost of
# of components, complexity, cost....

Lots to think about, lots to learn...

thanks for the post! ;)
 
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