The light in sodium vapour lampsodium vapour lampHigh-pressure sodium lamps are quite efficient — about 100 lumens per watt, when measured for photopic lighting conditions. Some higher-power lamps (e.g. 600 watt) have efficacies of about 150 lumens per watt.
› wiki › Sodium-vapor_lampSodium-vapor lamp - Wikipedia and mercury vapour lampmercury vapour lampMercury vapor lamps are more energy efficient than incandescent and most fluorescent lights, with luminous efficacies of 35 to 65 lumens/watt. Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output.
› wiki › Mercury-vapor_lampMercury-vapor lamp - Wikipedia is, because of electron emission.