Cheapest single 4 ft. fixture I found was on Amazon for $32.......... I believe 1 bulb should cover a 4 x 4 ft. area.
Sun Blaze HGC960320 T5 High Output Fluorescent 41-120 Volt-Indoor Grow Light for Hydroponic & Greenhouse Use-UL Listed, 4 ft. Fixture, 1 Lamp, 120V, Silver
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I purchased 3 of these units sshz, and all 3 were defective actually. (from amazon) I don't know if it's a technical issue, or if I simply got bad units, anyhow, thought I would throw that out there. I've done lots of testing and took one of the units apart (I've since got 2 units working) but replaced the ballast with American made 54 watt units, which are much bulkier and robust.
Anyhow, there's not much out there in this config, only allowing one light bulb, light and mobile units. (that's why I like them).
These are the ballast I purchased for replacement units.
I also got 2 jesco units that were almost identical to the above units, and they work fine. (I had to hack the power switches from the other units to get them to work) That said, I'm very happy once I got these things running, I can see a big difference in resin production, no question about it. I started with a few 15 min intervals/day then worked my way up to 30 min, then 1 hour. Right now I'm running them about an hour during the start of light, and a hour before lights out, so around 2 hours/day right now.
I'm using (1) 4 foot unit for approx 6x6 area, and there hanging about 3 foot above the canopy.
Oh, and I got a 4 pack of the T5 bulbs for $99 on amazon. Opened the box, and the package fell on the floor "boom" but the lights survived, thankfully. (they were wrapped very well).