||HPS lamps have long been the favoured light sources for plant growth, owing to the high proportion of radiation in the spectral range of greatest value to photosynthesis. Philips was an early pioneer in the development of lamps having a further optimised spectrum, for instance the SON Agro 400W. That features enhanced output in the blue as well as red regions to stimulate photosynthesis.
In order to increase growing yields, there has been a continual trend towards higher irradiation levels, which in turn calls for higher output lamps. However at levels above about 3000 lux the blue output (which prevents excessive vertical growth) becomes less important. This resulted in the GreenPower range of HPS lamps having only the increased red component, which raises performance because growth is stimulated much more by red light than blue.
To fuel the desire for still higher light levels, Philips launched the first 1000W plant growth lamp in 2005, in the form of this GreenPower TD. The double ended construction was chosen to maximise luminaire optical efficiency, because unlike for single ended lamps there is no frame support wire running alongside the arc tube, which may cast a shadow in the beam. The position of the arc tube with respect to the pinch-seals is also tightly controlled, which permits optimal positioning within the luminaire's optics. In common with most other double ended HPS lamps, the outer jacket is gas-filled rather than vacuum. This permits a reduction of arc tube length for a given wattage, further improving optical control. The high thermal conductivity of the gas filling does however make the lamp extremely sensitive to its environment in the luminaire, especially the reflector design.