Philips Horticultural Mercury HLRG 400W
The first dedicated light source optimised for plant growth was the Sylvania Gro-Lux fluorescent tube, having its energy concentrated in the red and blue wavelengths that maximise the rate of photosynthesis. However fluorescent lamps have a low intensity and higher light levels are often required. Many greenhouses resorted to more powerful high pressure mercury lamps, but neither their spectrum nor light distibution was ideal. Both problems were solved with the launch of this Philips HLRG 400W lamp in the late 1960s.

A major drawback of mercury lamps and luminaires at the time was their non-homogeneous light distribution when mounted at the short distances required to attain high enough levels of photosynthetically active radiation. Plants directly under the lamps received more light than others, leading to variations in growth rates and a need for frequent movement of plants. This was solved by employing an ellipsoidal reflector with deeply-mounted arc tube, which radiates more light at wider angles than directly under the lamp. It employs a half-aluminised large bulb of a 700W mercury lamp, and the glass is internally acid-etched to achieve a broader beam with high uniformity. The reflector portion of the bulb is coated with standard yttrium vanadate phosphor, although earlier versions employed the Philips magnesium arsenate phosphor.

This lamp was produced only for a few years - by 1978 it had been replaced by an improved version having a clear front and diffuse titanium dioxide reflector, which yielded a higher light output. It was produced until the mid 1990s when the superior spectrum of special high pressure sodium lamps had taken over the horticultural lighting market.
Manufacturer: NV Philips Gloeilampenfabrieken Model G/93/2
Lamp Power: 400 Watts
Lamp Current: 3.2 Amps
Lamp Voltage: 145 Volts
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Type: ED-140 ED-44 in eighths/inch
Bulb Finish: Aluminised + Phosphor Etched Borosilicate
Electrodes: Backwound tungsten BCY emitter
Arc Length: 72 mm 2.83 inches
Atmosphere: Inner: Hg | Ar (4.65 atm) Outer: Carbon dioxide
Luminous Flux: 14,000 lm @ 100 hrs
Luminous Efficacy: 35.0 lm/W @ 100 hrs
Colour Temperature & CRI: CCT:4500K CRI: Ra17
Chromaticity Co-ordinates: CCx: 0.365 CCy: 0.390
Lifetime: 12,000h 88% survival, 82% flux
Warm-up & Re-strike Time: 4 minutes 15 minutes
Burning Position: Universal Vertical cap up
Overall Length: 329 mm 13 inches
Light Centre Length: N/A N/A
Factory: Emmasingel, Eindhoven The Netherlands
Date of Manufacture: 1975 December Date Code: 5M
Original Value: Unknown
 
References: 1) Philips Lamp Catalogue 1970 International, p.F15
2) Example of later model 1978 HLRG 400W of Maxime Gendre
3) Philips Training Manual MTO Turnhoutlampen, Hogedruk-Kwiklampen, Van der Stap & Goethals, 1986.
4) Photometric Measurement, July 2020.