Fraction of the total luminosity density from stars at z ~ 2–6 emitted by galaxies in the rest-frame UV and in the mid-IR/far-IR (after dust reprocessing). In calculating the energy output in the UV vs. IR, we adopt the extinction estimates in Table 5 and assume that the total energy output from ULIRGs occurs in the infrared (see Section 6.3). A dotted line is included to show the relative contribution of LBGs and ULIRGs to the mid-IR/far-IR energy output. The contribution of star-forming galaxies is included all the way down to zero luminosity. Most of the energy output at z ~ 2–4 would appear to occur in the IR, while at z 5 the energy output occurs mostly in the UV. Note that despite most of the energy output at z~2.5–4 occurring at IR wavelengths, the SFR densities we derive from LBG surveys (after dust corrections) should account for 80% of the SFR density at z 3 (see Figure 14).