To get Surf on Pokemon Platinum,just when you exit the tall grass,near the MooMoo Milk shop on route 210 ,you see a group of PSYDUCKS (duck like Pokemon) grouped together. Cynthia (a girl who u meet on the way there) gives you a Secret potion in Valor Lakefront. Use it on the secret potionon the PSYDUCKS (the group of Pokemon) and they disappear. Cynthia gives you a Old Charm to give to her Grandma in Celestic Town. After facing 10-15 trainers, you arrive at Celestic town. I Reccomend you use the HM Defog, so the fog is clearer. Go fuel up your Pokemon at Poke Center, then go to The Celestic ruins. you will see Cynthias grandma in the ruins and start to talk to her. Then Galactic Boss (Cyrus) walks in and battles you. After beating him, Cynthia's grandma speaks to you and Gives you The HM Surf ,giving you access to Canalave City. THATS HOW YOU GET THE HM SURF!
i dunno wat u mean by light by to get it in platinum, the elder of solacean town will give it to you in the ruins
In Celestic Town you have to talk to the elder. A.K.A. Cynthia's Grandmother. She doesn't look special. She just looks like an old lady.