The sex of embryos in eggs is influenced or controlled through the application of light having selected wavelengths in order to promote the development of embryos of a selected sex. An incubating device is provided having an interior cavity that can be sealed from an outside, and having a plurality of lighting elements disposed on each of a plurality of trays disposed in the interior cavity. Eggs are disposed on the trays, and pre-determined environmental conditions are applied to the interior cavity to promote hatching of the eggs. Concurrently with the application of the environmental conditions, the eggs are irradiated according to pre-determined lighting conditions. The lighting conditions include applying light having wavelengths substantially concentrated in selected ranges, such as light wavelengths within the 390-419 nm, 410-450 nm, 420-450 nm, 450-495 nm, or other narrow range.
