Lighting and cooking heat are different functions. On a multi-cavity cooker, one failed lamp can make the appliance appear more broadly defective than the observations support.
What the observation means
Conversely, a bright lamp does not prove the oven is heating. Record each cavity's light, fan and food result separately instead of describing the entire cooker as on or off.
A useful next step
Check the normal lighting behaviour in the manual. Obtain compatible lamp advice only if replacement is permitted and no assembly damage exists. Do not open electrical sections to compare the powered cavity with the unlit one.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.