From FIG. 4 it can be clearly recognized that for the same sodium content of 12 to 20% the range of maximal efficiency of photosynthesis as compared with luminous efficiency is characterized by higher D-line reversal widths.
The desired D-line reversal width in praxi can be reached by increasing the cold spot temperature of the arc tube, whether by varying the distance of the electrode peak from the face of the tube or by application of heat build up bands at the outer surface of both tube ends. With unchanged tube dimensions the operating voltage of the lamp is increased thereby. Attention must be paid with regard to the fact that the lamp operating voltage is low enough to ensure a sufficient life of the lamp. Should the value of the lamp operating voltage be too high, a correction onto the desired value can be reached, also with constant D-line reversal width, by increasing the length of the discharge arc and reducing the diameter of the tube such that the wall loading of the arc tube per cm
2 remains constant. It must be observed that, as mentioned above, the arc length is not changed by more than 25%.
| TABLE 1 |
|
|
Photosynthetis |
Luminuous |
|
Efficiency |
Efficiency |
| % Na |
(Phytolumen/W) |
(lm/W) |
|
| 12 |
110-160 |
80-100 |
| 14 |
120-170 |
85-105 |
| 16 |
130-180 |
90-110 |
| 18 |
140-190 |
90-110 |
| 20 |
150-200 |
95-115 |
|
An example has been carried out for the case of a 400 W-amp.
Thereby the arc tube had the following dimensions:
inner tube length: 107 mm
inner diameter of the arc tube: 8.1 mm
Arc length: 84.6 mm
Wall thickness: 0.75 mm