I have an LED display circuit I am wiring up to a Raspberry Pi. It has a number of display cells that would each require a number of protective resistors, but I don’t have a particularly large number of spare resistors on hand. Can I gang together multiple LED cells onto a single resistor? The short answer is no, a single resistor only has enough power rating to support a single LED. Such a wiring would only work if you could guarantee that only a single LED was powered on at a time, such as a hardware multiplexer circuit. But failing that, say you have a shift register instead, you should use one resistor per LED.
Here is why. The typical power rating on resistors is 1/8 Watt or 1/4 Watt. A typical resistor with specifications around 2 V 50 mA will consume about 1/10 Watt power. With ceiling room allowance for double the power capacity to be on the same side, that really doesn’t leave you with any room at all for multiple LEDs on a single resistor. Definitely nothing on the order of 10, but maybe something on the order of 2 if you are careful.
20191106/DuckDuckGo resistor current rating
20191106/https://www.dummies.com/programming/electronics/components/electronics-components-resistor-power-ratings/
This site has some good info on how to calculate the required resistance nad power values for a LED’s protective resistor.
20191106/DuckDuckGo led current
20191106/https://www.sparkfun.com/tutorials/219