A Standard Candle?

The power law for the luminous intensity indicates that a current of 25.5 mA through the LED will produce an intensity of 0.50 cd. So two of them with the same current flowing through them should produce an intensity of 1.0 cd if both LED have the same characteristics. An LED with a square of luminous material whose side 1.25 that of the one in the measured LED would be capable of producing 1 cd at the same level of emittance. If the internal resistance is the limiting factor on the maximum current then reducing it will allow more light to be produced by the LED before failure and its V-I characteristic would be closer to that of an ideal diode.