Greenhouse Tomatoes

Should I use supplemental lighting to increase my yield?

The short answer to this question is no. However, if you want to understand the basis for this recommendation, read through this explanation. In order for supplemental lighting to increase yield, it must be bright enough to significantly increase photosynthesis. This means using High Intensity Discharge (HID) lamps giving about 1,000 foot candles each (or 400 watts, or 120 micromoles per square meter). One such lamp would be needed for each 40 square feet of greenhouse floor space. Therefore, in a 2,500 square foot greenhouse, a grower would need 62 lamps. Each lamp costs about $200. Therefore, the fixed costs (up front expenses) would be about $12,500 for a single bay greenhouse. But, then you would need to turn them on, too. Assume that you use these 62 lamps 12 hours each day, and 10 months of the year. Each lamp would provide about 425 watts, including the ballast. If your electricity costs 10 cents per kWh, your annual electric bill would be about $9,617. (If your electic cost is less than 10 cents per kWh, feel free to adjust this calculation.)

If you think you can increase your yield in the first year to bring in at least an additional $22,117, then you will more than break even. This would mean getting an additional 35 lbs. per plant (based on 500 plants in the greenhouse and selling at $1.25 per lb.). On the other hand, see the short answer above.