ðə mˈaɪnəs sˈaɪn ɔnðə lˈɛft hˈænd sˈaɪd ʃˈoʊz ðætðɪ ɪntˈɛnsᵻɾi dˈiːkɹiːsᵻz æz ðə bˈiːm tɹˈævəlz, dˈuː tə ðɪ ɐbsˈoːɹpʃən ʌv fˈoʊtɑːnz.
The minus sign on the left hand side shows that the intensity decreases as the beam travels, due to the absorption of photons.