Prodromoi

[hoplite14gr]

Also if you had accurate inteligence of the enmy´s strength and disposition you could arm the light cavalry with lances to attack light-non missle formations. If you didn´t shield and javelin and "hit and run" would be the order of the day which is the main role for light cavalry.
Byzantines had also light horse armed with lances, the trapezitoi. so lance had a use even for light horse but under specific circmstances and under proper conditions to be effective.
As I said I think that the reanctors proved that bare back charge with lance is possible. Usually this action would be carried out by heavy horse.
Only under "special conditions" such action would be done by light cavalry
Kind regards