Encounterdeath Note : Season 1 Episode 9 <CONFIRMED>

Light is forced to maintain a calm exterior while internally spiraling into a panic. He realizes L has trapped him in a perfect "checkmate" scenario:

If L dies shortly after revealing himself to Light, the Task Force will immediately know that Light is the culprit. EncounterDeath Note : Season 1 Episode 9

If Light tries to kill "Hideki Ryuga" using the Death Note, he would likely picture the famous idol instead of the person in front of him, resulting in the idol's death and confirming Light is Kira. Light is forced to maintain a calm exterior