In this study, thalli of brown seaweed Treptacantha barbata (Stackhouse) Orellana & Sansón were cultured under four colors of LED light (yellow, blue, green, and red) with cool white fluorescent light as a control, to test how the spectral composition of light affected their growth and biochemical composition under laboratory cultivation. The intensity was 100 μmol photon m2 s−1 of light. The specific growth rates, pigment and proximate compositions, sodium alginate, and fatty acid composition of the thalli were studied. The red LEDs provided the highest specific growth rate. The highest lipid content of the thalli of T. barbata occurred under both fluorescent light and green LED lights. Blue LED light produced the highest sodium alginate content (p ≤ .05). The results for fatty acid methyl esters showed that all four LED light sources influenced the fatty acid contents of T. barbata. The polyunsaturated fatty acid levels of T. barbata cultured in LED light sources were extremely high. We suggest that LED lights could be used to grow T. barbata in replacement of the fluorescent lighting currently used.