planck's quantum theory was based on observations of which of the following
Planck's law
U L 3 = ∫ 0 ∞ u λ ( T ) d λ , ( \ displaystyle ( \ frac ( U ) ( L ^ ( 3 ) ) ) = \ int _ ( 0 ) ^ ( \ infty ) u_ ( \ lambda ) ( T ) \ , d \ lambda , )
U L 3 = ∫ 0 ∞ u λ ( T ) d λ , ( \ displaystyle ( \ frac ( U ) ( L ^ ( 3 ) ) ) = \ int _ ( 0 ) ^ ( \ infty ) u_ ( \ lambda ) ( T ) \ , d \ lambda , )