Absolute vs. relative efficiency: How efficient are blue LEDs, actually?

The absolute internal quantum efficiency (IQE) of indium gallium nitride (InGaN) based blue light-emitting diodes (LEDs) at low temperatures is often assumed to be 100%. However, a new study from University of Illinois Urbana-Champaign Electrical and Computer Engineering researchers has found that the assumption of always perfect IQE is wrong: the IQE of an LED can be as low as 27.5%.