The outcoupling of light from AlGaAs-based light-emitting diodes (LEDs) can be improved by means of metal nanoparticles deposited on the surface of the device: light that would otherwise remain trapped in the highrefractive- index material by total internal reflection is scattered to the outside. We present an experimental study on the emission enhancement produced by single isolated gold nanoparticles of various sizes (60-150nm in diameter) and compare the results with numerical simulations. We find a clear enhancement as long as the dipole plasmon resonance of the particle is at a shorter wavelength than the LED emission. If the plasmon resonance coincides with the LED emission or is at a larger wavelength, the enhancement turns into damping. The simulations indicate that this latter effect is mainly caused by the particle quadrupole resonance producing absorption.