Thanks, that was the correct piece of code, usually it's handled automatically by the TileEntitySpecialRenderer superclass but since my tileentity was still a block it didn't work. It fixed itself as soon as I moved made the code get the lightvalue from 1 block in front of the tileentity instead.
int l = tileentity.getWorldObj().getLightBrightnessForSkyBlocks(tileentity.xCoord + dirWest, tileentity.yCoord, tileentity.zCoord + dirNorth, 0);
int i1 = l % 65536;
int j1 = l / 65536;
OpenGlHelper.setLightmapTextureCoords(OpenGlHelper.lightmapTexUnit, (float)i1, (float)j1);