| ADD TO CART |
DESCRIPTION | LAMP | PRICE |
|---|---|---|---|
| LU50/MEDED17TI |
HPS, 50W, Medium Base, Clear ED17 - 24 per Case | 5.36 | |
| LU70/MEDED17TI | HPS, 70W, Medium Base, Clear ED17 - 24 per Case | 5.36 | |
| LU100/MEDED17TI | HPS, 100W, Medium Base, Clear ED17 - 24 per Case | 5.36 | |
| LU150/MEDED17TI | HPS, 150W, Medium Base, Clear ED17 - 24 per Case | 5.51 | |
| LU70/MOGED23.5TI | HPS, 70W, Mogul Base, Clear ED23.5 - 24 per Case | 5.64 | |
| LU100/MOGED23.5TI | HPS, 100W, Mogul Base, Clear ED23.5 - 24 per Case | 5.64 | |
| LU150/MOGED23.5TI | HPS, 150W, Mogul Base, Clear ED23.5 - 24 per Case | 5.64 | |
LU250/MOGED18TI |
HPS,
250W, Mogul Base, Clear ED18 - 24 per Case |
6.34 |
|
LU400/MOGED18TI |
HPS,
400W, Mogul Base, Clear ED18 - 24 per Case |
6.76 |
|
LU1000/MOGET25TI |
HPS,
1000W, Mogul Base, Clear, ET25 - 12 per Case |
25.92 |
Theory of operation for High Pressure Sodium Lamps
An amalgam of metallic sodium and mercury lies at the coolest part of the lamp and provides the sodium and mercury vapor in which the arc is drawn. The temperature of the amalgam is determined to a great extent by lamp power. The higher the lamp power, the higher will be the amalgam temperature. The higher the temperature of the amalgam, the higher will be the mercury and sodium vapor pressures in the lamp. An increase in these metal pressures will cause a decrease in the electrical resistance of the lamp. For a given voltage, there are generally three modes of operation:
1. The lamp is extinguished and no current flows.
2. The lamp is operating with liquid amalgam in the tube.
3. The lamp is operating with all amalgam evaporated.The first and last states are stable, because the lamp resistance is weakly related to the voltage, but the second state is unstable. Any anomalous increase in current will cause an increase in power, causing an increase in amalgam temperature, which will cause a decrease in resistance, which will cause a further increase in current. This will create a runaway effect, and the lamp will jump to the high-current state (#3). Since actual lamps are not designed to handle this much power, this would result in catastrophic failure. Similarly, an anomalous drop in current will drive the lamp to extinction. It is the second state which is the desired operating state of the lamp, because a slow loss of the amalgam over time from a reservoir will have less effect on the characteristics of the lamp than a fully evaporated amalgam. The result is an average lamp life in excess of 20,000 hours.
In practical use, the lamp is powered by an AC voltage source in series with an inductive "ballast" in order to supply a nearly constant current to the lamp, rather than a constant voltage, thus assuring stable operation. The ballast is usually inductive rather than simply being resistive which minimizes resistive losses. Also, since the lamp effectively extinguishes at each zero-current point in the AC cycle, the inductive ballast assists in the reignition by providing a voltage spike at the zero-current point.
The light from the lamp consists of atomic emission lines of mercury and sodium, but is dominated by the sodium D-line emission. This line is extremely pressure (resonance) broadened and is also self-reversed due to absorption in the cooler outer layers of the arc, giving the lamp its improved color rendering characteristics. In addition, the red wing of the D-line emission is further pressure broadened by the Van der Waals forces from the mercury atoms in the arc.
