The "far-field" effect of metal nanoparticles (NPs), when chromophores localized nearby metal NPs (typically the distance >lambda/10), is an important optical effect to enhance emission in photoluminescence. The far-field effect originates mainly from the interaction between origin emission and mirror-reflected emission, resulting in the increased irradiative rate of chromophores on the mirror-type substrate. Here, the far-field effect is used to improve emission efficiency of polymer light-emitting diodes (PLEDs). A universal performance improvement is achieved for the full visible light (red, green, blue) PLEDs, utilizing gold (Au) NPs to modify the indium tin oxide (ITO) substrates; this is shown by experimental and theoretical simulation to mainly come from the far-field effect. The optimized distance, between the NPs and chromophores with visible light emission ranging from 400 to 700 nm, is 80-120 nm. Thus the scope of the far-field may overlap the light-emitting profile very well to enhance the efficiency of optoelectronic devices. The 30-40% enhancement is obtained for different color-emitting materials through distance optimization. The far-field effect is demonstrated to enhance device performance for materials in the full-visible spectral range, which extends the optoelectric applications of Au NPs.