A light emission device is provided, including a first substrate and a second substrate facing the first substrate. The light emission device further includes a vacuum vessel between the first substrate and the second substrate. An electron emission unit is on the first substrate. A light emission unit is on the second substrate. A heat transfer medium is in the vacuum vessel. The heat transfer medium is adapted to absorb and to dissipate generated heat of the vacuum vessel. The second substrate includes an active area and a non-active area surrounding the active area. The heat transfer medium is in the non-active area.