Method for manufacturing direct backlight unit, fluorescent lamp and backlight unit

1. A manufacturing method for a direct type backlight unit, comprising the steps of:

preparing a plurality of fluorescent lamps, each of the fluorescent lamps having a non-phosphor layer area of a first length at a first end, a non-phosphor layer area of a second length at a second end, and light emitting properties that are different from each other at a first end side and a second end side;

detecting, with use of a sensor, a length of the non-phosphor layer area at least one of the first end and the second end; and

installing the plurality of fluorescent lamps in a housing with use of a result of the detection, so that the first end and the second end alternate on a same side of the housing.

2. The manufacturing method for a direct type backlight unit of claim 1 , wherein for each of the fluorescent lamps

in the detection step, using a boundary between a non-phosphor layer area and a phosphor layer area as a reference, a distance from the boundary to a predetermined position of a constituent element of the fluorescent lamp is detected with use of the sensor.

3. The manufacturing method for a direct type backlight unit of claim 2 , wherein

each of the fluorescent lamps further includes a pair of electrodes, each electrode being disposed on an inner side of a different one of the first end and the second end, and

in the detection step, a distance from the boundary to a base of at least one of the electrodes is detected with use of the sensor.

4. The manufacturing method for a direct type backlight unit of claim 2 , wherein

each of the first and second end portions of each of the fluorescent lamps further includes a lead wire projecting outward, and

in the detection step, a distance from the boundary to an outer tip of at least one of the lead wires is detected with use of the sensor.

5. A fluorescent lamp including a glass bulb and a phosphor layer formed on an inner face of the glass bulb excluding ends thereof, wherein

a length of a non-phosphor layer area extending from one of the ends of the glass bulb and a length of the non-phosphor layer area extending from another of the ends of the glass bulb are sufficiently different so as to be identifiable by a sensor.

6. The fluorescent lamp of claim 5 , wherein

an identifying mark pertaining to detecting lengthwise orientation has been provided on one of an outer circumference and an inner circumference of the non-phosphor layer area of the glass bulb.

7. The fluorescent lamp of claim 6 , wherein

a plurality of the identifying marks have been provided at respective positions on the outer circumference of the glass bulb, the positions corresponding to the non-phosphor layer area,

the plurality of identifying marks have been provided so as to be at positions substantially equivalent to each other in the lengthwise direction of the glass bulb, and such that one or more of the identifying marks is visible from a direction regardless of a revolution direction of the glass bulb, and

the plurality of identifying marks have been provided so as to have one or more intervals therebetween in the revolution direction.

8. The fluorescent lamp of claim 5 , wherein

the difference between the length of the non-phosphor layer area extending from the one end of the glass bulb and the length of the non-phosphor layer area extending from the another end of the glass bulb is greater than or equal to 2 [mm].

9. The fluorescent lamp of claim 5 , wherein

both of the ends of the glass bulb have been pinch-sealed to form pinch-sealed ends,

a lead-in wire and a gas exhaust tube have been inserted through at least one of the pinch-sealed ends, the lead-in wire functioning as a power supply route to an internal electrode, and an outer end of the gas exhaust tube being sealed, and

the fluorescent lamp further comprises:

a base that is electrically connected to the lead-in wire and affixed to one of the gas exhaust tube and a portion of the glass bulb excluding the pinch-sealed ends.

10. The fluorescent lamp of claim 9 , wherein

the base is sleeve-shaped and affixed to an un-pinch-sealed portion of the glass bulb, the un-pinch-sealed portion being a portion of the glass bulb other than the pinch-sealed ends.

11. The fluorescent lamp of claim 9 , wherein

the gas exhaust tube extends outward from at least one of the pinch-sealed ends, and the base has been affixed to an extending portion of the gas exhaust tube.

12. The fluorescent lamp of claim 5 , further comprising:

a pair of bottomed tube-shaped electrodes, each electrode being disposed on an inner side of a different one of the first end and the second end; and

a fluorescent lamp emitter containing magnesium oxide, whose primary particles are formed from single crystals, formed on at least a portion of one of an inner face and an outer face of at least one of the electrodes, an average particle diameter of the single crystals being less than or equal to 1 [μm].

13. The fluorescent lamp of claim 5 , further comprising:

a pair of bottomed tube-shaped electrodes, each electrode being disposed on an inner side of a different one of the first end and the second end, wherein

an electrode material of at least one of the electrodes is composed of nickel as a base material, yttrium oxide in a range of 0.1 [wt %] to 1.0 [wt %] inclusive having been added to the electrode material.

14. The fluorescent lamp of claim 13 , wherein

any of silicon, titanium, strontium and calcium has been added to the electrode material in a content amount that is less than or equal to half of a content amount of the yttrium oxide.

15. The fluorescent lamp of claim 5 , wherein

a mixed gas including argon gas and neon gas has been enclosed in the glass bulb,

letting a charged pressure [Torr] of the mixed gas be plotted on an x axis and a drive current value [mA] be plotted on a y axis in an x-y orthogonal coordinate system, the charged pressure of the mixed gas is a coordinate value of x and the mixed gas drive current value is a coordinate value of y that are in an area enclosed by a line (including the line) drawn sequentially between points represented as (x,y) coordinates, the points being (10,10), (10, 7.6), (21,6), (31,4), (49,4), (51,6), (52,8), (53,10), and (10,10), and

the mixed gas contains argon gas at a partial pressure rate of greater than or equal to 20[%].

16. The fluorescent lamp of claim 15 , wherein

the charged pressure of the mixed gas and the drive current value are, respectively, in an area enclosed by a line (including the line) drawn sequentially between points represented as (x,y) coordinates in the x-y orthogonal coordinate system, the points being (10,10), (10, 8.5), (13,8), (30,6), (44,6), (47,8), (50,10), and (10,10).

17. The fluorescent lamp of claim 16 , wherein

the charged pressure of the mixed gas and the drive current value are, respectively, in an area enclosed by a line (including the line) drawn sequentially between points represented as (x,y) coordinates in the x-y orthogonal coordinate system, the points being (10,10), (10, 9.3), (27,8), (39,8), (46,10), and (10,10).

18. The fluorescent lamp of claim 17 , wherein

the charged pressure of the mixed gas and the drive current value are, respectively, on a line that connects points represented as (x,y) coordinates in the x-y orthogonal coordinate system, the points being (10,10) and (32, 10).

19. A backlight unit including the fluorescent lamp of claim 5 in a housing.

20. A liquid crystal display apparatus including the backlight unit of claim 19 .