# How big should battery be to power two strips of led for few hours?

I have an idea for halloween costume for upcoming Halloween. It will involve building two small sets of infinity mirrors. I am completely new to the electrical engineering. The infinity mirrors require any light source in between two one-way mirrors. I want to use a small LED strip for each sets.

How large battery would be needed to power two small LED strips for hours? Suppose I have a headset that already holds two AA batteries for speakers that I will never use, will those two batteries suffice or should I dig it out and use that space to hold other kind of battery?

Which is the best small/thin LED strip should I purchase to maximize brightness and minimize power consumption?

EDIT: Since that many LED strips have their LEDS spaced too wide on the strips. (Many offer 6 ft of LED strip, I only need like 1 foot but the same amount of LEDs crammed in it.) I decided to use electroluminescent light (EL) instead. Will that change the equation of energy consumption a lot?

• Sadly, shopping questions are off-topic. electronics.stackexchange is about designing electronics. Pleas read help center for advice on how to ask good questions which may get good answers. Commented Sep 25, 2014 at 2:39
• You can get answers to your question by measuring the diameter of the circle of LEDs, converting that value to a strip length, and searching the web. It usually comes in lengths of multiples of 1 metre. A reasonably dense LED strip, say 30 single colour LEDs/metre, i.e. a 1m/π diameter circle, would likely take at least 0.01A/LED, and hence at least 0.3A/hour, two strips 0.6A/hour. More LEDs, more current. Guess 2 good quality AA's might last a couple of hours Commented Sep 25, 2014 at 2:40
• Most LED strips run on 12V, with 2 AAs you would need a boost converter to get appropriate voltage. Quick estimation: two strips 21 LEDs each (7 segments with 3 diodes), at 20 mA, with 70% effective converter and 2000 mAh batteries at 1.2V. Run time is 2000/(21/3*2*20)/(12/2.4)*0.70=1h. Commented Sep 25, 2014 at 2:40
• @venny they can run at less than 12V too. 10~14V, 14~22mA Commented Sep 25, 2014 at 5:59
• Also, Infinity mirrors only need one one-way mirror. The inner one can be a regular mirror. Commented Sep 25, 2014 at 6:00

## 1 Answer

Buy an LED strip and a cheap multimeter. Then power the strip with the battery and measure the current with the meter. Take the current and multiply by the time you want to use it for, in hours. So if it draws 0.5 A and you want it to last 2 hours, then you multiply 0.5 amps times 2 hours to get 1 amp-hour. Batteries are rated in amp-hours, so connect enough of them in series to get the voltage you need, and then connect enough in parallel to get the capacity you need (battery amp hour does not change in series, but they add in parallel: two 1 Ah batteries in series form a 1 Ah battery at twice the voltage, two 1 Ah batteries in parallel form a 2 Ah battery at the same voltage). I don't think a pair of AA batteries will get you the run time you want, though.