No test with 400w MH, but a comparison was done between 250w MH, 6x39w T5HO and LED's.
Feature Article: Quantitative Comparison of Reef Aquarium Lighting Technologies: Metal Halide, T5 Fluorescent and LED | Advanced Aquarist's Online Magazine
"A 250W double ended USHIO 14000K lamp in a Sunlight Supply Lumen Max 3 reflector driven by a "HQI" M80 ballast was used a representative of the class of metal halide lamps.
Peak values of PAR achieved were 278 micromoles/m2/sec at distance 24" from the center of the lamp, and 190 at 30" from the lamp center.
The power consumption for this combination was 306 Watts."
"The 36"ATI Powermodule with 6 X 39W T5 lamps was claimed by many to be among the best in the class among the T5 fixtures and considered to be similar in power consumption to a 250W Metal halide setup. A representative lamp ATI EcoLux High Output 6500K lamp was chosen to perform the analysis for light distribution (primarily since I was able to acquire 6 of lamps easily).
Peak values of PAR achieved were 220 micromoles/m2/sec at distance 24" from the center of the lamp, and 161 at 30" from the lamp center.
The power consumption as measured by a true RMS watt meter was 254 W."
"The PFO Solaris LED fixture was a 24" 2X30 LED array, with a mix of blue, white and a couple of green LEDs.
Peak values of PAR achieved were 213 micromoles/m2/sec at distance 24" from the center of the lamp, and 160 at 30" from the lamp center.
The power consumption as measured by a true RMS watt meter was 216 W."
"The Eco-Lamps KR92 fixture (
http://www.eco-lamps.com/) . A 24" version, with 91 LEDs was tested to evaluate the light distribution from some of the current generation of LEDs that are available in the market.
Peak values of PAR achieved were 224 micromoles/m2/sec at distance 24" from the center of the lamp, and 160 at 30" from the lamp center.
The power consumption as measured by a true RMS watt meter was 110 W."