The infinitive is the base form of the verb, before the verb is conjugated. For example: to speak, to eat, to live are English verbs in the infinitive form; to + verb creates the infinitive of a verb in English. In Spanish the infinitives of verbs have three diferent endings: ar, er and ir.
Light dependent reactions produce ATP and NADPH from energy captured from light. Therefore without light it cannot proceed. Light independent reactions fix carbon dioxide into glucose using the ATP and NADPH produced in the light dependent reactions. So light independent reactions can occur without light as long as CO2, ATP and NADPH is present.
I'm assuming you're talking about photosynthesis. The main difference can be seen in the terms. Light dependent need light to react, light independent do not. In the light reactions the photon of light hits the chlorophyll which excites an electron that goes into the electron transport chain. This electron comes from water being split into H+ ions and oxygent gas.