I recently took advantage of post-Christmas sales and purchased several strings of warm white C7 size LED lights of 25 in each string. My intention is to brighten the window candles we currently have. Initially, when I designed the candles last year, I used a single light from each string in place of the original candle bulb. I used a DC "wall wort" 12 volt power supply to power each one with a dropping resistor to reduce the current in each bulb to around the 17 mA level, the same level I measured in the 120 V string before I cut the bulbs out to use them. However, this left the bulbs too dim and the wife didn't like the dimness. Then, a few days ago, since there's enough room inside the bulb envelope, I doubled up two bulbs in series and adjusted the current going in to be around 40 mA. Using the two series bulbs in each candle envelope brightened the result considerably, but now I'm concerned that there may be too much current flowing through them. Although I didn't measure it, I believe the current in series bulbs remains the same (40mA) but the voltage divides(?). This may be too much for the bulbs.
Today, in an experiment, I decided to wire four bulbs in parallel and set the input current at 10 mA. Measurements were 2.7 VDC @ 10 mA going into the parallel combination. Four bulbs inside these small envelopes begins to get difficult, but still not impossible.
My goal is to have the longest life possible out of these candles and the maximum brightness which is the reason I've dropped the input current and/or used more than a single bulb for each candle.
I have several questions:
1) If I use either the four bulbs in parallel driven at 10 mA and/or the two bulbs in series at 40 mA input, is the resulting output brightness going to be the same for the bulb combinations?
2) Which is the best method to use for preserving the longest LED life?
Thanks in advance, Sam