High-Pressure Sodium- HPS Lamps are probably the most innovated bulb on the market for flowering. There are many shapes, sizes and brands of bulbs. For every HPS bulb, you need a rated ballast for it. 35, 50, 70, 100, 150, 200, 310, 400, 600 and 1000 watt bulbs all require a ballast. A 1000w bulb needs a 1000w ballast. Some ballasts are switchable from HPS to MH, and some are switchable from 110v-220v. It is completely necessary to use the rated ballast for each bulb, as each are very unique on how they run. Some HPS bulb companies include (but not limited to): Philips (SonAgro), Westinghouse (Ceramalux), Sylvania (Lumalux), GE (Lucalox), EYE (Hortilux). HPS run on the red, orange and yellow band, around 630nm. This is most comparable to the harvest sun, which is why they are most ideal for flowering. An HPS lamp operates by passing electricity through vaporized mercury and sodium within the arc tube.
High pressure sodium lamps vary between 90/150 lm/w (A 1000w bulb will typically emit 100,000+ lumens). 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. 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. This sometime poses a problem for new growers. When using an HPS light, plants tend to have more “empty” space in between nodes, which is mostly just wasted space. Most experienced growers prefer using fluorescent or MH lights in the vegetative state to avoid this. Plants that get too big, too fast, often have issues during the flowering stage. They get too big to support themselves, and require more light/water/nutrients to survive. Most growers will argue, that although HPS lights WILL grow your plants bigger and faster, that doesn’t always mean you’ll have a bigger yield. Metal Halide lights emit the blue spectrum, which will promote slower, thicker (bushier) growth. This, typically, is what most growers prefer. Smaller, bushier plants take up less room. The flower of the plant will look different depending on the type of bulb used. If using an HPS light through the entire life of the plant, you will notice “popcorn” buds throughout the plant. This is because of the long spaces between nodes. When budding a smaller, bushier plant, it will seem as if the entire stem is a bud, because there is little room between nodes.
At the end of life, high-pressure sodium lamps exhibit a phenomenon known as cycling, which is caused by a loss of sodium in the arc. Sodium is a highly reactive element, and is easily lost by reacting with the arc tube made of aluminum oxide and the products are sodium oxide and aluminum:
6 Na + Al2O3 → 3 Na2O + 2 Al
As a result, these lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the maximum voltage output by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, repeatedly. The major disadvantage to using HPS lights, is that they create a lot of heat. If you have an open faced hood, it’s difficult to keep the temperature down enough to keep it close to your plants. That’s why it’s recommended to use a hood that has a glass insulation cover and ventilation holes on the side so you can hook up an exhaust fan to help keep things cool. This will allow you to keep your light as close as possible without burning them up, so you can make the most of your light. Below is a guide for how many lumens are lost with the distance your light is from your plants.
Pros: High Pressure Sodium lights are currently the industry-leading choice of light bulb. It has the best overall lumen/watt ratio, the strongest intensity, a wide range of spectrum and last much longer then other traditional growing bulbs.
Cons: High Pressure Sodium bulbs are rather expensive, both initial cost and power consumption. They produce a lot of heat, and if not properly installed they can be dangerous. If not properly ventilated, they can pose heat problems and potentially burn your plants.
HPS emery consumption chart
HID Light Output Primary Growing Area Supplemental Area
100 watts 2′ x 2′ 3′ x 3′
250 watts 3′ x 3′ 4′ x 4′
400 watts 4′ x 4′ 6′ x 6′
600 watts 8′ x 8′ 12′ x 12′
MH (Metal Halide)
MH (Metal Halide) is a member of the high-intensity discharge (HID) family of lamps. They produce high light output for their size, making them a compact, powerful, and efficient light source. Like other gas-discharge lamps such as the very similar mercury-vapor lamps, metal-halide lamps produce light by making an electric arc in a mixture of gases. In a metal-halide lamp, the compact arc tube contains a high-pressure mixture of argon, mercury, and a variety of metalhalides. The mixture of halides will affect the nature of light produced, influencing the correlated color temperature and intensity (making the light bluer, or redder, for example). The argon gas in the lamp is easily ionized, and facilitates striking the arc across the two electrodes when voltage is first applied to the lamp. The heat generated by the arc then vaporizes the mercury and metal halides, which produce light as the temperature and pressure increases. MH emits mostly blue, which is why growers find it suitable for vegetation. They allow your plant to grow at it’s own rate; unlike when using HPS, the plant feels the need to grow faster. Using MH during vegetation ensures a grower a bushy, fulled out plant. The nodes will be closer together apposed to using HPS.
Pros: Metal Halide lights go hand-in-hand with High Pressure Sodium lamps, being the industry’s leading source of light. They produce very good lumen/w output, offering a wide range of spectrum (mostly blue) and are relatively cheap. They are the best suitable for vegetation; normally providing a very even and bushy growth.
Cons: Metal Halide lights “burn out” faster than other grow bulbs (about 1/2 the life of a typical HPS). They run very hot, much like HPS lights, so ventilation is a must. Metal Halide lights also (unless a dual ballast) require there own type of ballast.
Some important terms to know:
Measure of electrical power (w)
Measure of electrical charge (v)
Measure of color temperature (K)
Measure of light brightness (lu)
tecnically correct term for a HID "bulb".
Measure of light intensity (cd)
Measure of electrical current
A distinctive line of light produced by the shield in a headlight that blocks light above a certain height in order to prevent blinding of other motorists.
The pattern of light that is projected onto the ground which includes angle of lateral dispersion, width and depth of illumination.
Another term for an HID bulb. Some refer to HID bulbs as gas discharge capsules.
The lighting control assembly structured around the bulb, which effects the dispersion of light and it's characteristics to a great degree.
HID (High Intensity Discharge)
= Gas Discharge
1500 k Candlelight
2700-2900 k Yellow painted fog halogen bulbs
3200 k Sunrise/sunset
3200 k Premium H7 non painted halogen bulb
3400 k 1 hour from dusk/dawn
4100 k Philips/Osram OEM HID D2S
5500 k Bright sunny daylight around noon
5500-5600 k Electronic photo flash
6000 k Philips Ultinon HID D2S
6500-7500 k Overcast sky
9000-12000 k Blue sky
28000 Northern sky
12000-30000 k Ultra Violet light (black light)