Ok, I'm not really trying to reverse resistance but here's the problem I've got with an assignment question. The question itself is measuring light, so when light falls below a certain level an LED flashes. I've got a CdS cell running into a NPN transistor (acting as a switch depending on the current coming from the CdS cell) which then triggers a 555 timing chip to control the LED flashing. Now all that works fine except for the fact it's doing the exact reverse of what it's supposed to do. ie. When there is plenty of light (ie. low resistance in the CdS cell) the LED flashes, but when there is low light it doesn't flash. Is anyone able to give me a pointer on how I could reverse this? I'll keep reading up on it but any pointers would be appreciated.