I bought some LED string lights before Christmas and we had them in the office, for some random cheer. The lights were mixed colours, red green and blue. They were powered by two AA batteries, and we left them on continuously for more than a week. After a while I thought some of the lights were broken but later someone else pointed out to me that only one colour remained lit.
With only the green LEDs apparently lit, the voltage measurement on the battery was 1.153 V (1.156 V with no current flowing). A fresh battery capable of lighting all the colours of LED provides a voltage of 1.311 V with the current flowing (1.325 V with no current flowing).
Strangely green LED’s are the least efficient colour, so it’s strange they would be the last ones lit…
For change in voltage, red LEDs take the least to work, and as the colour moves up the colour spectrum toward blue, the voltage requirement increases (green is between red and blue).
So does this mean these LED’s aren’t really naturally green ones, and rely on phosphor filtering? Or some other technology?
Is this a problem of perception of brightness of different colours?