Backlight device and display apparatus

A backlight device comprising:

• a substrate having a principal surface;
• a plurality of light-emitting elements, supported by the principal surface of the substrate, that emit excitation light;
• a first phosphor layer containing a phosphor that produces fluorescence upon receiving the excitation light;
• and
• a partitioning member forming a plurality of spaces each of which accommodates any one or more of the plurality of light-emitting elements between the principal surface of the substrate and the first phosphor layer,
• wherein
• the partitioning member includes
• a plurality of walls each of which, in a top view, encloses the one or more of the plurality of light-emitting elements accommodated separately in each of the plurality of spaces,
• a plurality of apices each of which connects ones of the plurality of walls that are adjacent to each other,
• one or more first through-holes formed in the plurality of walls, and
• one or more second through-holes formed in the plurality of apices,
• an air gap is formed between adjacent two walls of the plurality of walls by the two walls and one of the apices that connects the two walls, and
• a second through-hole formed in the one of the apices among the one or more second through-holes communicates with a first through-hole formed in one of the two walls among the one or more first through-holes via the air gap.