Mycelial browning, which protects the organism from contamination and moisture loss, is essential for sawdust cultivation of Lentinula edodes. The effects of light and light wavelengths on the mycelial browning of the L. edodes Sanjo 701ho strain, and the characteristics of its brown hyphae, were investigated. After the mycelia were cultured on potato dextrose agar medium under fluorescent lamps covered with colored cellophane filters (red, green, and blue) or under light emitted diodes (LED), with wavelengths ranging from 400 to 700 nm (far-red, red, green, and blue), for 14 h per day for 40 days, the mycelial browning rate was measured. The wavelength of fluorescent lamps, which range from 300 to 1,100 nm, was reduced to 360 to 1,022 nm with the use of three colored cellophane filters and the photosynthetic photon flux density was reduced by 42 to 71 % depending on the light wavelength. The browning rate by colony area of mycelia exposed to light was at an average of 64 %, whereas, that of unexposed mycelia was only 5 %. The browning rate was 0.02 % in far-red, 1.5 % in red, 53.8 % in green, 57.3 % in blue, and 64.0 % in fluorescent light. The white mycelia were resilient with actively growing hyphae, filled with cytoplasm, and thin cell walls less than $1{\mu}m$ thick. Conversely, the brown mycelia possessed dead, hard hyphal structures without cytoplasm, but with approximately $2-4{\mu}m-thick$-thick cell walls. In conclusion, lights of varying wavelengths, especially short-wavelength LEDs, are effective for forming dead, brown mycelia of L. edodes, thus, forming a protective functional layer for its living white mycelia.