Flashers automatically support all colors of 20ma LEDs with no additional resistors required. Colors can be mixed on the same circuit. Will drive multiple LEDs in series depending on power supply voltage. Resistors can be added to on-board solder pads for LED brghtness control. Input: 7-16V DC Less than 1′ square. LEDs sold separately. Alternately flashes a pair of LEDs (or up to 4 pair depending on power source). Each light is on for 3/4 second, typical of grade crossings, school zones etc.WARNING: This product can expose you to chemicals including LEAD, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov