How much lighting do I need for growing lettuce using indoor hydroponics?

Question

I am beginning to get into indoor hydroponics to grow lettuce, I haven't figured out which type of lettuce to grow yet, I am thinking of a butterhead. I have been to many hydroponics stores and seen almost all the lettuce hydroponics videos on youtube. When it comes to lighting, no one has an accurate answer. The store is trying to push a huge T5 lighting system. But I think its overkill. Now I have bought a Light Meter, to test various lights.

How many lumens do I need for lettuce to grow?

I'm trying to figure out the costs involved with the electricity of the lights.

Answer 1

Lettuces don't need a lot of light to grow. I recently read "The Winter Harvest Handbook" by Elliot Coleman and in it he describes growing lettuces in the winter in Maine (Zone 5) in the dead of winter underneath two layers of insulating row cover. They don't grow fast as in summer, but they do grow.

The nice thing about leaf crops (which lettuce is) as opposed to fruit crops (like tomatoes that have to flower to produce the part you want) is that as long as you can keep it alive it doesn't really matter how big or vigorous it grows, you can just grow more of them.

I have metal halide lights indoors and the lettuces that I plant underneath them flower and go bitter in about 8 weeks - hardly worth the effort.

My advice would be to go to home depot and get some shop lights which are 40W fluorescents or something similar. They are cheap and easy. You can spend money for the grow bulbs but I would not bother at this point. Start small and experiment, you can add more if you like.

BTW, if you are in a cold climate where the inside air in the winter is very dry you will get better results if you enclose your growing area as much as you can and do everything you can to keep the humidity up.

Answer 2

I have had success with an 80 watt compact fluorescent light (CFL) within 5 cm of the plants, you can grow at least 6 plants. Unlike metal halide and high pressure sodium lights you can position the light close to the plants without burning them. Also you don't need a ballast just a standard screw fitting for the light.

This page might be helpful under the heading: How much light should plants receive?

Incidentally using a CFL light is a great way to start seeds. It amazing how easy it is to start seeds (even temperamental varieties) with CFL light and a heating mat.