When using Optifine and holding light emitting items/blocks, they cast light around you so you can see. I feel holding the lantern could look better with a 3D model that shows you holding it by the chain above the lamp(in both 1st and 3rd person), but I lack the skills to properly model such. For Resource Pack support, only the model shown when held, and the position of such should be changed.
Alternately, if you know how to change the model/position of a held item, feel free to let me know how it's done.
This represents rotation, translation (position) and scale of your model in various views, like 1st person or 3rd person. Experiment a bit with these settings to match your model. This ^ above is just an example. Note that this is for minecraft 1.8. In 1.9 and above there is no "thirdperson" or "firstperson", instead we have "thirdperson_righthand" "thirdperson_lefthand" "firstperson_righthand" and "firstperson_lefthand"
I'm sure you can find a detailed guide through this somewhere on the internet.