Combined Model With Multiple Lights, Metallic Highlights and Distance Attenuation

I_[l] = I_amb[l] + sum[i]( I_diff[l] + I_spec[l] ) for N lights
= k_a[l] I_a[l] O_d[l] + sum[i]( f(d_i)( k_d[l] I_li[l] (N^.L) O_d[l] + k_s[l]([l], [t]) I_li[l] (N^.H)ⁿ O_d[l] ) )

Where di is distance to light i

Possible f(d_i) = 1 / (a₀ + a₁ d_i + a₂ d_i²)

a₁ d_i - linear falloff
a₂ d_i² - quadratic falloff