Supplementary lighting with high-pressure sodium lamps is widely used to increase the yield of greenhouse vegetables and cut flowers. To achieve the maximum benefit from their lighting, growers are advised to change the lamps after an indicated time. The lamp changes are necessary because the light output gradually decreases over time.
Based on the physical principles of a high-pressure sodium lamp, the decrease of light output is accompanied by an increase in lamp voltage. Once the maximum voltage is reached the power supply turns the lamp off. At this point, it is necessary to change the lamp in order to protect the power supply from damages.
Another factor, which has a direct impact on the voltage is the lamp temperature: the higher the temperature, the higher the voltage. This means that a higher lamp temperature reduces the lifetime because the switch off voltage will be reached earlier.
In order to reduce the temperature of the lamp BLV has designed an open reflector. The openings in the reflector create a chimney effect, which optimizes the lamp temperature. Measurements taken with an integrated temperature sensor show that the outer temperature of the lamps is 8 % lower in a luminaire with an open reflector, compared to one with a closed reflector. This data indicates that the lifetime of lamps in open reflectors increases by more than 10%.
Although the effect of a lower lamp temperature can vary between lamps and luminaires, these findings clearly show: Using an open reflector helps you to increase the lifetime of high-pressure sodium lamps, which translates directly into a reduction of maintenance and replacement costs.