# Why are these LED current limiting resistors so big?

I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:

If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the current through the LED to 6 mA just to keep the brightness low? The datasheet for the charger has 470 Ohms resistors in the reference design too. I'm just not sure why.

• Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need? – Dave Tweed Feb 3 at 22:36
• If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that. – Hearth Feb 3 at 22:37
• You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785 – Ale..chenski Feb 4 at 3:53
• 6 mA x 3V = 18 mW. Assume 150 lm/Watt from LED at low current. At 150 lm/W = 27 lm. Look at that at say 1metre and assume radiation angle of LED is such that it illuminates 1/4 say of available area. Full sphere = 4Pir^2 so 1/4 sphere at 1m = Pi^R^2 = 3.14 m^2. Illuminance = 27 lm /3.14 ~= 10 lm/m^2. That's nicely visible but not bright-distracting-bright. Sounds good. E&)E. – Russell McMahon Feb 5 at 10:40