I wanna know a value of the unity_Lightmap_HDR.

I’m testing many things with the Unity5 to start new project with it.
so I’m trying to recycle a lightmap baked already at the other scene.
but I found out lightmap color is changed when I see it at other scene.
after I look into the UnityCG.cginc, I found the unity_Lightmap_HDR.
I think value of the unity_Lightmap_HDR is changed at the other scene.

so I wanna know how to know value of the unity_Lightmap_HDR after bake.

I wanna know, too!
Change light map’s texture type to default and then can I use that in custom shader?
like this:

half4 col = tex2D(_MainTex, i.uv0.xy);
half4 lightmap = tex2D(_Lightmap, i.uv1.xy);
col.rgb = col.rgb * DecodeLightmap(lightmap);

help me!
thanks!