local debug      = false
local spacelight = default.space_light_generic
local tick       = 0

minetest.register_globalstep (function (dtime)
    tick = tick + 1
    if tick < 5 then return end
    tick = 0

    for _, player in ipairs (minetest.get_connected_players()) do
        local pos = player:getpos()

        if pos.y >= 0 and upper_realms.is_outer_space (pos.y) then
            local minp = vector.round (vector.subtract (pos, 8))
            local maxp = vector.round (vector.add      (pos, 8))

            local vm     = minetest.get_voxel_manip()
            local e1, e2 = vm:read_from_map (minp, maxp)
            local area   = VoxelArea:new { MinEdge=e1, MaxEdge=e2 }
            local ltdata = vm:get_light_data()
            local chg    = false
            local asun
            local info

-- The "+ 1" used in the following code block is a  work-around for an
-- apparent bug in the MT mapgen API.

            for ii in area:iterp (minp, maxp) do
                local sun = ltdata [ii] % 0x10
                local nat = ltdata [ii] - sun
                if    nat <       ((spacelight + 0) * 0x10) then
                    ltdata [ii] = ((spacelight + 1) * 0x10) + sun
                    asun = sun
                    chg  = true

                    if debug then
                        info = nat .. " " .. sun
                    end
                end
            end

            if chg then
                if debug then
                    ocutil.log ("spacelight " .. info)
                end

-- "vm:update_liquids()"  should  be  omitted here.  It seems to cause
-- more problems than it solves.

                vm:set_light_data (ltdata)
                vm:write_to_map (false)

-- The following code updates just one node, at the player's position,
-- in a different way. This may or may not help.

                local node = minetest.get_node (pos)
                if  node.name ~= "ignore" then
                    node.param1 = ((spacelight + 1) * 0x10) + asun
                    minetest.set_node (pos, node)
                end
            end
        end
    end
end)