Indoor gardeners and urban farmers alike, need control over: light, water, heat, nutrients, CO2, and in many cases electricity. A perfect balance of these six factors will produce perfect plants every time. The challenge in the equation is an endless supply of variables within those six factors. Every garden is different in some way (location, types of plants, water quality, air quality, light source, fertilizer, and farming methods). There is no blanket explanation as to how much of each environmental factor to provide in every garden. For optimal results, more attention must be paid to the environment we provide for our crops.
To begin, let’s look at some of the variables within our lighting choices. Options include sunlight, HID lighting, fluorescent lighting and LEDs. If sunlight is available, use it. Sunlight is reliable, free and includes every color wavelength. Hobby gardeners can grow a wide variety of houseplants and herbs year round by simply taking advantage of the available windows. Notable drawbacks of sunlight are excess heat, excess UV, the limiting day length of our Fall and Winter months, and the enthusiast’s tendency to want a larger grow plot than their windows can provide light for.
Artificial lighting comes into play when we want to grow plants out of season, on multiple tiers, or in environments with inadequate or no access to daylight. Traditional plant lighting has the same basic drawbacks as the sun: excess heat and UV. While HID and fluorescent bulbs are not limited by the time of year, they are limited by their own wavelength composition, lifetime and energy requirements. Generally, less than 20% of the wavelengths emitted are actually useable by your plants. Bulb replacements create a recurring cost in your system and the increased energy requirements can outweigh the benefits in many commercial applications. LEDs manage excess heat in an effort to keep temperature and humidity down. With LEDs it makes sense to add heat, until temperature and humidity levels are optimal. An ideal environment would utilize a mixture of sunlight and LEDs. If no sunlight is available, HID and LED in combination provides the best lighting solution for a year round indoor gardener. Simply use your HID to control your temperature and humidity, and use your LEDs to provide the light for photosynthesis…that’s simple. Remember, photosynthesis makes the fuel plants use for growth, and PAR (400nm-700nm) will not make plants drink water, or ‘make’ plants grow larger fruits, without help from heat.
Once you’ve decided on the type of lighting that best meets your needs, the next variable to consider is how many hours per day you will use it? When we are gardening with sunshine, our day length is preprogrammed by the solar system. Once artificial lighting enters the mix, every hour of lighting carries a cost in both energy and lamp replacements. Using the average cost of electricity in the United States, we can estimate approximately what this cost will be.
|Type of Bulb||Hours of Operation||Cost Per Day||Expected Lifetime|
|1000 Watt HID||12||$1.32||12,000-24,000 Hours|
|600 Watt HID||12||0.79||12,000-24,000 Hours|
|400 Watt HID||12||0.53||12,000-24,000 Hours|
|54 Watt 4’ Fluorescent||12||0.07||20,000 Hours|
|9 Watt LED||12||0.01||100,000 Hours|
Once you have determined the day/night schedule that best meets your plant needs there is also the question of how far from the plants to mount your light source. Again, the sun is going to make this decision very easy. The relatively low output means fluorescent tubes should be mounted from 6”-12” above your plants, which is also close enough for the lamp to add heat to your plants. Both HID and LED lighting have a wide range of possibilities. The closer your lights are to the plants, the greater the intensity. Low watt LEDs can be placed as close as 2” from the plant canopy and HID can be placed as close as possible without physically burning your plants. The distance for HID will depend on the size of your bulb and is generally somewhere between 18”-30”. Increasing the distance from your plants will increase the coverage area (while decreasing the intensity). HID lighting can be placed as far as 10’ from the plant canopy and LED lighting as far as 4’. Check in next to learn how your lighting choices will have a direct effect on both the watering schedule and heat requirements of your garden.
Angela Lundmark is the editor of the LED Gardener and CEO of LED Grow Master Global, LLC.