High Pressure Sodium - HPS
High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in plants to increase flowering/budding in plants. They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.

Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum. If a gardener were to start a young plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most plants would grow up thin and lanky and in no time you will have to prune your plant back before it grows into the light fixture. The exception to this is using HPS grow lights in a greenhouse or in conjunction another light source that emits light in the blue spectrum. Light sources that have a high output in the blue spectrum like sunlight and MH grow lights offset any stretching caused by HPS bulbs. View MH & HPS grow lights

.
Fluorescent Plant Grow Lights

Until recently, fluorescent grow lights have had a low output and have been too big and bulky to be of much use as a grow light for anything more than starting seedlings. CFL and T5 full spectrum fluorescent lights have changed that. At 75 to 90 lumens per watt, these lights are energy efficient and extremely effective especially when used in numbers. Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights. This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant. It is recommended that these lights be placed no more than a couple feet from the plants for best results. 2700k to 3000k bulbs provide higher output in the red spectrum which promotes flowering. 5000k to 6500k bulbs are full spectrum with much of the light in the blue spectrum which promote overall green plant growth. View (CFL) compact fluorescent grow lights, View T5 fluorescent tube grow lights

The standard T12 bulbs full spectrum tubes are fine for starts and seedlings and are popular for growing low-light plants like herbs and African violets. These lights are inefficient and are be replaced with high efficiency T5 lights which are a better light source for flowering and budding applications as well. View T5 fluorescent grow lights

Incandescent Plant Grow Lights

These lights are the most inexpensive to purchase but are also the most inefficient and a poor source of light for plants. At best they can provide supplemental light to individual house plants. Incandescent lights have a low lumen output per watt compared to HID and fluorescent grow lights. New smaller CFL grow lights like our 40 watt Green Thumb system produce as much light as a 150 watt incandescent bulb, and more of the light is used by the plant. This type of bulb will pay for itself in energy savings the first 60 days of use.

LED Plant Grow Lights

LED grow lights are the newest lighting option for plants. They are advertised to be the most efficient and coolest running grow lights available. We have tested several different types of LED grow lights and have found none that outperform much cheaper fluorescent grow lights of similar wattage. LED plant grow lights are also not recommended for use with plants that you want to be viewed, because they give plants an unnatural appearance when the light is on.

Light Output Comparison Chart

Each scenario above represents approximately 50,000 lumens.

Grow Light Comparison Chart
Grow Light	Watts	Growing Area		Heat Output	Recommended Light Height Above Plants	Bulb Life (hours)
		Primary	Secondary
Incandescent	150	0.5' x 0.5'	1' x 1'	Medium	1' to 2'	2,000
CFL	40	1' x 1'	2' x 2'	Very Low	3" to 1.5'	10,000
CFL	125	2' x 2'	3' x 3'	Low	6" to 2'	10,000
CFL	200	2.5' x 2.5'	4' x 4'	Low	6" to 2'	10,000
2' T5 (single)	24	1' x 2'	1.5' x 2.5'	Very Low	3" to 2'	20,000
2' T5 (2 bulbs)	48	1.5' x 2.5'	2' x 3'	Very Low	3" to 2'	20,000
2' T5 (4 bulbs)	96	2' x 3'	3' x 4'	Low	6" to 2'	20,000
4' T5 (single)	54	1' x 4'	1.5' x 5'	Very Low	3" to 2'	20,000
4' T5 (4 bulbs)	216	2.5' x 5'	4' x 6'	Low	6" to 3'	20,000
4' T5 (8 bulbs)	432	4' x 6'	6' x 7'	Low	1' to 3'	20,000
HPS	250	3' x 3'	5' x 5'	Medium	2' to 3'	24,000
HPS	400	5' x 5'	8' x 8'	High	3' to 4'	24,000
HPS	600	6' x 6'	10' x 10'	High	3' to 4'	24,000
HPS	1000	8' x 8'	12' x 12'	Very High	4' to 6'	24,000
MH	250	3' x 3'	5' x 5'	Medium	2' to 3'	10,000
MH	400	5' x 5'	8' x 8'	High	3' to 4'	10,000
MH	1000	8' x 8'	12' x 12'	Very High	4' to 6'	10,000
Growing Area Back to Chart The growing areas listed above assume the light bulbs are being used in a fixture with a reflector similar in quality to the ones offered on this web site.
Primary - Use the area in this column if the grow light will be the main or only source of light for the plants. This includes areas where minimal light comes from windows or standard house/office lights.
Secondary - Use the area in this column if the grow light will be used in a greenhouse or other area that receives direct sunlight for part of the day to supplement the light from the sun.
Heat Output Back to Chart The chart above uses a combination of the light bulb temperature and the dimensions of the bulb(s).
Bulb	Average Bulb Temperature		.	Bulb	Average Bulb Temperature
T5	100 to 120° F			Incandescent	220 to 260° F
CFL	130 to 180° F			MH/HPS	450 to 550° F
How Long Should Grow Lights Run?
This depends on the type of plant. Foliage plants need about 14-16 hours of light per day. Flowering plants need 12-16 hours of light per day. You should give most plants at least 8 hours of total darkness daily. Try to have the lights on at the same time every day. You can get an automatic timer for your lights to make it easier.
The Electrical Cost to Run a Grow Light System
To get the operating cost per hour for a light, take the lights combined wattage, and divide it by 1000 to get the kilowatts used. Then multiply that number by the amount your electric company charges per kilowatt hour. HID lights will use the number of watts it emits per hour, ie; 600w system will use 600 watts per hour (regardless of spectrum). (light wattage output / 1000) x electricity cost per kilowatt hour = Operating cost per hour operating cost per hour x hours used per month = Operating cost per month

How the Sunlight Affects Plant Growth

Grow Light Systems Section