Low pressure mercury vapor discharge lamp and manufacturing method therefor

In a low pressure mercury vapor lamp, the improvement comprising:

• an arc tube having a plurality of connected U-shaped glass tubes with a fluorescent layer provided at an internal surface of each U-shaped glass tube, each glass tube a circular cross-sectional pair of straight leg portions connected with a curved portion wherein an internal dimension of the glass tube at a center of the curved portion fulfills the following condition:
• 0.5<d1/D≦0.9
• wherein d1 is the interior cross-sectional distance at the center of the glass tube curved portion and D is a diameter of the glass tube on straight leg portions of the U-shaped tube;
• and wherein a discharge distance is approximately 301 mm.

A low pressure mercury vapor discharge lamp comprising a U-shaped glass tube having a smoothly curved bend and two straight leg portions;

• the bend having a cross-section with an interior curve and an exterior curve, the interior curve being approximately a chord;
• and,
• where the smoothly curved bend has a shortest internal diameter of d1 and where the two straight legs have an internal diameter of D and where a ratio of d1/D is 0.5<d1/D<0.8,
• wherein the exterior curve is a circular arc having a substantially uniform radius.

A low pressure mercury vapor discharge lamp, comprising:

• a plurality of U-shaped glass tubes, wherein the U-shaped glass tubes are connected and form a discharge path;
• at least one U-shaped glass tube having a smoothly curved bend and two straight leg portions;
• the bend having across-section with an interior curve and an exterior curve, the interior curve being a gentle curve;
• where the bend has a shortest internal diameter of d1 and where the two straight legs have an internal diameter of D and where a ratio of d1/D is 0.5<d1/D<0.8,
• a holder for holding an arc tube;
• a lighting circuit for applying lighting voltage to the arc tube held by the holder between ends of the discharge path;
• and
• a lamp cap that is integrated with the holder, the lamp cap connecting the lighting circuit to an external power,
• wherein the exterior curve is a circular arc having a substantially uniform diameter.

A low pressure mercury vapor discharge lamp comprising:

• a plurality of U-shaped glass tubes, wherein the U-shaped glass tubes are connected and form a discharge path;
• at least one U-shaped glass tube having a smoothly curved bend and two straight leg portions;
• the bend having a cross-section with an interior curve and an exterior curve of a circular arc of substantially uniform diameter, the interior curve being a gentle curve;
• where the bend has a shortest internal diameter of d1 and where the two straight legs have an internal diameter of D and where a ratio of d1/D is 0.5<d1/D<0.8;
• a holder for holding an arc tube;
• a lighting circuit for applying lighting voltage to the arc tube held by the holder between ends of the discharge path;
• and
• a lamp cap that is integrated with the holder, the lamp cap connecting the lighting circuit to an external power,
• wherein the bend of each U-shaped glass tube has the same cross-section.