The Swedish telegraph was capable of being used at night with lamps. On smaller stations lamps were placed behind the shutters so that they became visible when the shutter was opened. For larger stations, this was impractical. Instead, a separate tin box matrix with glass windows was installed below the daytime shutters. The lamps inside the tin box could be uncovered by pulling strings in the same way the daytime shutters were operated. Windows on both sides of the box allowed the lamps to be seen by both the upstream and downstream adjacent stations. The codepoints used at night were the complements of the codepoints used during the day. This made the pattern of lamps in open shutters at night the same as the pattern of closed shutters in daytime.