LED runtime for a small and strange application.

JKR

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I may attempt a strange little LED project but I am not sure it is worth doing based on the runtime of the LED that I may get. I stopped at Radioshack and picked up a green LED lamp with mount with the following specs:

Fwd voltage: 2.1V at 20mA Max current: 30mA

I also bought a 3V 160mAh CR 1/3 N lithium battery (replaces L768BP) for power.

Before I drill a mount hole for this, can anyone tell me what the runtime projection would be? The leads would likely have to be permanently mounted and this thing has to be very compact for the application. I am unsure how to calculate the runtime of this setup.

Thanks,
JKR
 

Meduza

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If we choose a resistored setup with a 39 ohm resistor we would get a circut that draws around 25ma

160mah = 160ma in one hour

160mah / 25ma = 6.4

So around six hours is a good guess :)
 

JKR

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Thanks.

Well, I guess this isn't going to work for what I need it too. Based on the LED throwie website and discussed here, I thought I might get a week out of it. I guess their approx of 1-2 weeks with a 2032 battery is VERY optimistic, if not downright wrong.
 

Sub_Umbra

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JKR said:
Thanks.

Well, I guess this isn't going to work for what I need it too. Based on the LED throwie website and discussed here, I thought I might get a week out of it. I guess their approx of 1-2 weeks with a 2032 battery is VERY optimistic, if not downright wrong.
I read the throwie thing, too. I'm not a modder or a builder and i'm not well versed in electrical math but let me throw in something from recent experience.

I was just doing a runtime test of a cr2032 cell a couple weeks ago. I bought 50 for my Photon Freedom. (green LED) It wasn't a conventional runtime test to 50% because I'm interested in only using this light at very low brightness levels. I put one of the new cells in it, set it on high and let it go. I got bored with the test (and wanted to carry the light again) after about 12 days. It was below 50% but still surprisingly bright. I can see where it's brightness when I stopped the test would certainly still be bright enough for a throwie, IMO. I haven't messed around with 2032s before but I was really surprised at how long one brightly lit an LED.

Hope this helps.
 

JKR

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Thanks for the info.

I am a little confused at this point. I purchased the above battery because it LOOKED as though it would have a greater amount of run-time due to the size vs the 2032. The 2032 battery is a larger diameter but much more thin compared to the battery I have.

Likewise, I seem to recall someone questioning the claimed run time on the throwies. Seems like someone projected a significantly shorter runtime than the throwie webpage indicated.

I might be better to go with a blinking LED for my particular application. It would offer better runtime and still serve the purpose that I need it for.

Thanks,
Justin
 

Sub_Umbra

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Green and blue/green LEDs will also look brighter than other colors throughout the life of the cell since the human eye is able to utilize that part of the spectrum best. As an example, a green LED will look ~70% brighter than a white one that uses the same amount of power, IIRC.

There are some other factors involved in this, but if you can work green into the design you'll have a light that will be brighter, longer.
 
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thesurefire

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Sub_Umbra said:
Green and blue/green LEDs will also look brighter than other colors throughout the life of the cell since the human eye is able to utilize that part of the spectrum best. As an example, a green LED will look ~70% brighter than a white one that uses the same amount of power, IIRC.

There are some other factors involved in this, but if you can work green into the design you'll have a light that will be brighter, longer.

This is correct. Green will look the brigestest. I think the most sensitive green is around 510 on the color scale thing.
 
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