Your photocell is a LDR (Light Dependent Resistor) The more light striking the photocell, the lower the resistance and eventually your LEDs light. With your circuit as it is you can't change the light/dark and how it works. Also, even as it is, it is not a very good circuit.
You don't mention the supply voltage (battery voltage) or anything as to the LED specifications like the forward current or forward voltage?
You would do well to build what you want (dark = LEDs On) using either a transistor or a comparator. This would allow you more control, especially a comparator with hysteresis as to LED On and LED Off at what light levels striking the LDR sensor.
Ron