Higher current-densities begin to produce continuum emission. Spectral lines broaden and become less dominant as light is produced across the spectrum, usually peaking, or "centered", on a certain wavelength. Optimum output-efficiency in the visual range is obtained at a density that favors "greybody radiation" (an arc that produces mostly continuum emission, but is still mostly translucent to its own light; an effect similar to sunlight when it passes through a cloud). For xenon, greybody radiation is centered near green, and produces the right combination for white light. Greybody radiation is produced at densities above 2400 A/cm2.