The significant number of Lyman alpha emitting galaxies observed at high redshifts and recently at low z with GALEX provides now a picture of
the evolution of Lyman alpha emission over a large range of redshift. The GALEX sample improves over previously known nearby emitters by its statistical significance. Since Ly-a emission is affected by resonant scattering, the Ly-a evolution is appreciated by comparison with the evolution of massive star. We present a comparison in terms of luminosity density (LD).
From z=0 to z about 3, the Ly-alpha LD increases slightly faster than the UV LD, suggesting a possible increase of the average Ly-a escape fraction as a function of redshift. Beyond z=3, if the UV LD declines as shown by some authors, there is again a slight increase of the average Ly-a escape up to z=6. At the epoch of reionization, the LD comparison is probably less appropriate than the direct comparison of Ly-a LFs for a search of increased IGM opacity.