The pentene changes to colorless very quickly. The pentane changes after exposure to the overhead's light.
The light-catalyzed reaction between an alkane and bromine can be stated as follows:
Chain initiation: Br2 + hv --> 2 Br.
Chain propogation: Br. + R-H --> R-Br + H.
H. + Br2 --> H-Br + Br.
Chain termination: 2 Br. --> Br2
2 H. --> H2
H. + Br. --> HBr
An NSF funded Project