The Growers House staff has had countless discussions (read: arguments) over what bulbs perform best. We decided to put our best guesses to rest by testing out a portion of the most popular bulbs in the market, concluding in one of the most interesting--and expensive--tests we've ever done. We decided to test the most popular grow light style, 1000w High Pressure Sodium bulbs.
To test the effectiveness of these bulbs we kept all variables constant except the bulb, which we tested nine. We used the Phantom 1000w 120/240v digital ballast and the OG Vertical reflector hung 24 inches above a footprint with a marked off grid where we measured 7 different points. Each bulb was given 20 minutes after firing to warm up to operating temperature and intensity. We then used a Photosynthetically Active Radiation (PAR) Meter to measure the intensity of light in the spectrum that plants use to photosynthesize.
We used this meter instead of a luxmeter because measuring lux or lumens only measures the light visible to the human eye. Lumen measurements are used for HID bulbs when they were used as street lamps (their original use), to translate the brightness to the human eye, not necessarily the brightness in the spectrum that plants use to photosynthesize. The PAR meter measures the intensity of light within the spectrum 400 nanometers to 700 nanometers, which encompasses the wavelengths--both red and blue--that plants use to photosynthesize.
Notes--This test was very illuminating, no pun intended :) Before reading into the numbers, we have some things you should keep in mind. Bulb manufacturers admit that there could be up to a 5% variance +/- in bulb output, even though they are made by the same factory under relatively similar conditions. That said, the majority of the bulbs were within 0.01% of each other in terms of their PAR reading in the center of the grid. That's extremely close and leads us to believe that they are made very similarly. The bulbs that stood out were Digilux, Ushio, and Hortilux. Another important note is that the farther away from the center, the more the PAR measurements fluctuated. The measurements off from the center also sometimes didn't correlate with how well the bulb did in the center reading. We aren't exactly sure why this is, but we have a guess: because reflectors use pebbled aluminum (including the OG vertical Reflector) we believe that the pebbled finish reflects the light in ways that could cause the irregularities that we saw in our test.
Conclusion-- Eye Hortilux Enhanced 1000 watt HPS came out the undisputed winner in this test being almost 10% better than the next best bulb. The Ushio and Digixlux, came in next very close to each other, and about another 10% above the rest of the pack. The next five bulbs were similar in readings, yet the Maxlume bulb is quite a bit less expensive than all of them, leading us to conclude that it's the best value bulb. What was somewhat surprising was the reading we got from the Dual Arc. Since Dual Arc's are made up of a 600w HPS and a 400w MH, we expected the output to be lower because MH bulbs are less efficient at converting wattage into intensity, but we thought that the more full spectrum of a Dual Arc may counter the decreased efficiency of the MH bulb. We were wrong and it seems that the HPS bulbs still produce more intensity in the spectrum plants use to photosynthesize than Dual Arc bulbs.
Bulbs Tested: Eye Hortilux 1000w Enhanced HPS, Ushio 1000w Opti Red HPS, Digilux 1000w HPS, Advanced Nutrients Baddass Bulb 1000w HPS, Solis Tek 1000w HPS, Lumatek 1000w HPS, Maxlume 1000w HPS, GrowLite 1000w HPS, and a Ultra Sun 1000w Dual Arc*.
*We tested the Dual Arc Ultra Sun bulb because we were interested in seeing how they compared to other 1000w HPS bulbs.
Click infographic below to enlarge.