Ask Erik

Hello Eric,

Thanks for the question. You might get some different answers depending on whom you ask. I’m not sure which gardening forum might be best but I would suggest hanging out at your local hydroponic shop. Growers may be able to achieve faster growth rates in traditionally lower light requirement crops such as lettuce by increasing the light intensity, particularly when supplementing carbon dioxide (CO2) levels. However, the additional heat associated with higher light intensities must be managed, as lettuce is sensitive to excessive temperatures and “bolting” may occur. In popular literature, many light recommendations have been made assuming warmer temperatures come with higher light. Today’s grower may not have that same limitation. A light meter would be the best way to determine ideal lighting levels. Different light meters give readings in different units: from micromoles to micro-Einsteins, to lumens. There is much literature available to recommend ideal light levels as per light meter units specified. As mentioned, you may not encounter the same limitations, and choose to push the envelope a bit. If you see the edges of the leaves looking scorched, back off on the light and or temperature. As long as you can maintain growing temperatures of less than 70°F, the plants should be able to make good use of higher light levels. At a guess, it sounds like you have it right. You might be able to put the lamp closer to the plants, just make sure it doesn’t get past 70°F at the canopy. Remember that watts per square foot is only an accurate reference when everyone assumes the same distance from the lamp. For a 250 watt lamp, growers requiring high light intensities may have plants as close as eight to 12 inches away from the HID source. The MH lamps is an excellent choice, as the spectrum (blue light) may help keep the plants from bolting, even under higher light intensities.

Cheers, Erik