How many lumens per watt of high pressure sodium lamp?

Answer:

One watt of high pressure sodium lamp is 120 lumens.The lumens of luminous flux is a physical unit description, physics for a candle (CD, Candela Candela, unit of luminous intensity, the equivalent of an ordinary candle light intensity) in a solid angle corresponding to the spherical cone ball (1 square meters of the unit sphere radius of 1 meters on the representative point,

Any size ball of the total solid angle is 4 PI, so the total luminous flux of the candle is fixed for 4 PI, do not change because of the change of distance, so the total luminous flux of 1 candles around the launch position about 0.28M 1 lumens is false statement.

The total luminous flux produced on the corresponding center of the cross section is about 65 degrees. Considering the solid angle of the whole sphere is 4 PI, and the total luminous flux of 1 candles is 4 PI (12.57) lumens