HPS Grow Light

February 28th, 2010
HPS Grow Light Bulb

HPS Grow Light

One of the most important things to think about when growing your plants indoors is appropriate light. A proper grow light is one of the main factors which can guarantee you the biggest harvest in the smallest amount of time. Light is one of the energy sources the plants need in order to grow and give you the most impressive products. In fact, it directly depends on it: for example if you reduce the light by half you get a two times smaller harvest. So if you get poor results when growing your plants indoors than light should be the first factor to question.

There is a handful of different lights used for growing plants. Some of them are used for specific phase of plants life (like vegetation or flowering) while others can be used for both phases. The spectrum color that a lamp produces is important, because plants grow best under different colors depending on their stage of maturity. See the spectrum chart below. HPS grow light is best suited for flowering phase (when the plant is blooming or bearing fruit) because it emits red/orange spectrum light. But a lot of growers use it for the vegetation period as well with a combination of blue spectrum fluorescent lights or withouth them. Blue spectrum lights are better for fruiting or vegetative phase and red spectrum lights are better for flowering phase. In fact, nowadays there are modern blue spectrum enchanced High Pressure Sodium grow lamps (like SON Agro lights). This means that they can be used in all phases of a plants growth. You can expect a bigger harvest with these lamps compared to the regular HPS lamps.

Kelvin Temperature chart

Kelvin Temperature chart

HPS grow lights can simulate the natures lightning (which is the sunlight) very well. Thats why they’re often called HPS/SON lights. Most of the time a proper indoor grow light system is even better when the natural lighting. That is because you allways have the best conditions – there are no cloudy days which is inevitable when the plant is growing outdoors.

HPS system produces more light output per watt of energy consumed than most of other lamps. See the table below. HPS grow light bulbs are relatively small units that produce a great amount of light. That is another reason why people choose HPS grow light for their indoor gardens.

HPS Grow Light efficency comparison
Lamp Type Watts Lumens/bulb Total efficiency
Fluorescent Bulb 40 3000 30k lumens
Mercury Vapor 175 8000 20k lumens
Metal Halide 400 36000 36k lumens
High Pressure Sodium 400 45000 45k lumens

HPS lights are gas discharge lights. They emit light when electrical current flows through an ionized gas or plasma. HPS lamps produce light when sodium becomes excited. HPS lights can’t run without pre-heating and voltage control. A remote elctronic system known as ballast is needed to start the lamp. A ballast is mechanism that acts as a type of resistor. Its purpose is to regulate the amount of electrical current flowing through a circuit. If we switched an HPS lamp without a ballast than the bulb would explode because of uncontrolled voltage. The ballast ensures that only the required amount of current flows through the arc.

A lifetime of an HPS grow light is from twelve to eighteen months. While these lamps continue to light for a longer period than 18 months, their efficency drops up to 30 percent or even more. That is because more energy is needed to maintain high pressure of the gas and less energy is transformed into light. When the ballast cannot supply the required amount of voltage it starts shutting down the arc – the temperature drops down and the pressure of the gas inside the tube reduces. When the temperature is safe to operate the ballast turns the light on again. However, when you see this happening, it’s really time to think about replacing the bulb.

One of the downsides of HPS light is that it generates a great amount of heat. So you may need to use some kind of cooling system like fans to cool the lamps and the environment they’re in. If the environment is too hot near the top of the plants, you need to lift the lamps higher. You will kill the plant if it’s overheated. On the other hand, a good cooling system can reduce the distance from plant to lamp. And if this distance is shorter, the plant gets more light. And i’ve already wrote about how it affects the final result.

Another factor you have to consider before starting to use HPS lights is a reflactor. A reflector increases light intensity to the direction where the plants are (this way you get more efficiency) and eliminates hot spots. You should mount HPS lamp horizontally. This will boost by 30% the amount of light that actually reaches the plants.

HPS lamps are available in a wide variety of sizes and wattages. Common wattages range from 70 to 1000 watts and the size of a blub depends on the wattage: the bigger the wattage – the bigger the bulb. If you want better results from your yields, you should consider a bigger wattage lamp. The bigger the wattage, the more light is emmited. And light is very important. I will try to write more about this in another post.

Choosing a grow-light carefully is one of the most important things when starting an indoor garden. A modern HPS grow light setup with a blue spectrum added is a perfect choice.

HPS Grow Light Wattages

March 23rd, 2010

HPS grow lights come in a wide variety of wattages. The bigger the wattage of the lamp, the more light will be emitted. In order to get the optimal results from your indoor garden, you need to choose the right size HPS grow light. This will ensure vigorous growth and a plentiful yeild. Insufficient light will result in weak plants and small yeilds.

As you probably know, light flow can be measured in lumens (lm). One lumen is equal to the flow of light which is emitted from a very small wax candle. HPS grow lights can produce more than 140 lm/W (lumens per watt) in the same time when “standard” incandescent light bulb produces about 18 lm/W. As we can see, HPS bulbs are very efficient.

Before buying a lamp for your indoor garden, you need to know what is its area and how much light do you need for this area. An intensity of light which falls on a surface can be described in luxes. 1 lux equals to 1 lumen per square meter (lx = lm/m2). When we know what light intensity we need per square meter, we can decide what bulb(s) should we buy. On a clear summer day, sun gives about 50000 lux at the earth surface. Most of the plants need as more light as possible for fastest growth and biggest harvests. You should try to supply from 25000 to 50000 lux light for the best results. Your plants will say thank you. 10000 – 15000 lux is a minimum for sparse growth. The table below shows approximate lighting of different wattage bulbs. You should note that HPS bulb light intensity differs from manufacturer to manufacturer.

HPS Grow Light Illumination Chart
Watts Lumen lm/W
70 6300 90
150 16000 107
200 22000 110
225 27500 122
250 29000 116
360 46000 127
400 50000 125
430 52000 120
600 87000 145
940 130000 138
1000 140000 140

Usually the lights with bigger wattages are more efficient. The illumination values show us what amount of light is emmited when the lamp is placed directly above the plants.

In all cases you should try to put your source of the light as close as possible to the plants for maximum lumen intensity. However HPS bulbs can give off large amounts of heat (especially the ones with higher wattages). If you put the lamp too close to the plant it can get burned and die. On the other hand if you put the lamp too far away from the plant, you will loose some lamp efficiency. That is why you should know how to determine the optimal light sources height from the plant. If you use a good cooling system, the lights distance from the plants can be shorter.