If you have a 400-watt HID and it will not supply adequate light coverage to a; "4x2.5 room" you either have the wrong reflective hood, terrible reflective material or both. I know people that grow in areas that are 5' X 5', if not slightly larger, using a 400-watt HID and they have all the light they need, all the way down to the bottoms of their plants and all the way out to the edges of their most outer plants.
Some people do not realize the importance of picking the right or correct or best reflective hood, and one of very high quality, for the space they grow in and they do not realize how important reflective light is. Roughly 40% of a yield will come from the outer portions of plants and what makes or breaks the quality of that percentage is how good someone's reflective material is.
You could put a 600-watt HID in there and if you picked the wrong reflective hood and used poor reflective material if wouldn't be enough lighting to do the job. Some reflective hoods focus the light into such a narrow/small footprint that they cannot cover the size area the actual wattage is capable of covering. Others, like batwing designs, are open ended and you lose a large amount of light to the sides that even with good reflective material is never fully utilized because it will not all be reflected down or back against the plants and instead some will be reflected back under the light and upwards.
Maybe you just need to look for a large wide coverage high quality reflective hood and if your reflective material is not high quality consider upgrading it.
One guy I know uses a Big Kahuna hood he bought from HTGS for his 400-watt HID and he said it made all the difference in the world over his old hood.
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And I have read on sites like this where people have said the same thing about the XXXL Magnum.
- Maximum air cooling with built-in 6″ fittings
Magnum XXXL 6″ Air-Cooled Reflector
- The largest reflectors in the industry!
- Reflector dimensions: 32 1/2″ long x 26 1/4″ wide x 7 3/4″ tall
- Includes tempered glass, built-in socket & 15 ft. lamp cord
- Completely sealed – featuring gasketed glass and integrated retention bars to hold glass tightly in place
- 95% reflective German aluminum interior offers excellent reflectivity and diffusion
- Re-strike bend above the lamp for optimum performance
- Powder-coated galvanized steel body
- Maximum air cooling with built-in 6″ fittings
I have read where some people claimed they were too large to use with a 400-watt HID and you should use a 600-watt or 1000-watt with them, but the guy I know who uses one uses his Big Kahuna with a 400-watt HID and he said the difference was like night and day in how how plants grew and responded once he switched to it and I have read the same basic thing about the XXXL Magnum.
You might want to consider just upgrading your hood and possibly your reflective material too, depending on what you now use.
Those are just examples, but something that you need to shoehorn into your space and would throw light everywhere might be all you need to change.
