What is the difference between High Pressure Sodium Bulbs and Metal Halide bulbs.
Although high pressure sodium bulbs and metal halide bulbs are both types of HID (High Intensity Discharge) lights, they emit different color spectrums.High pressure sodium bulbs have a very bright reddish-yellow light and lack and blue or violet light. Metal halide bulbs are balanced and contain much more of the visual spectrum.
Another difference is the lumens per watt of both bulbs. Lumens is the measurement for the efficiency of the bulb or how much light you're producing for the amount of electricity you're using. High Pressure Sodium bulbs appear very yellow-orange and produce between 97 and 150 lumens per watt. Metal halide bulbs appear more blue-white and produce 65-115 lumens per watt.
How long will my HPS or MH bulb last
Metal halide bulbs should be changed at least every 6 to 12 months if running them 18 hours per day. High pressure sodium bulbs, running at 12 hours per day, will last between 6 months and a year and a half, depending on the bulb.
You need to weigh multiple factors when selecting a bulb for your grow room.
If you have natural light, use High Pressure Sodium bulbs to make the days longer in the spring and fall. They are great for days that don't have a lot of light or places that are grey.If you don't have access to natural light, Metal Halide bulbs provide a very wide light spectrum, making them great for grow rooms.For vegetatative grow, use a Metal Halide bulb
Another thing to consider is your bulbs efficiency. High Pressure Sodium bulbs put out more light per watt and last twice as long as Metal Halide bulbs.
Should I use Metal Halide bulbs for growth and High Pressure Sodium bulbs for flowering?
There are a couple of reasons growers switch between bulbs during different stages of plant growth. Metal Halide bulbs are good at the beginning because they cause plants to grow tighter, (with less spacing). Starting with high pressure sodium bulbs will cause your plants to get leggy or stretch out and metal halide bulbs will prevent this.Consequently, some people use metal halide lights during vegetative growth to keep the structural growth of the plant nice and tight, but switch to sodium bulbs during the flowering stage when plants need more light.Indoor growers often switch to a high pressure sodium light for flowering because the red yellow light significantly promotes flowering and fruiting.
Do both bulbs work on the same ballast?
No. Never interchange bulbs between systems unless they are specifically designed to do so. Lots of people ask if they can use a 1000 watt bulb in a 400 system and the answer is NEVER! It's dangerous; the bulb could become unstable and explode. You should also never put halide bulbs in a high pressure sodium system or high pressure sodium bulbs in a metal halide system. The ballasts are only meant to run the type of bulb they are rated for. These are the general guidelines. Your equipment may be different and it is always recommended you consult the manufacturer before doing anything out of the ordinary.
But I've heard of conversion bulbs, what are they?
Conversion bulbs let you use the opposite of whatever your system is. So if you have a high pressure sodium system, you can now run a metal Halide bulb and vice versa. You get the best of both worlds with the conversion bulb. You don't have to switch you ballast and reflector you just switch out a bulb. Metal halide bulbs for vegetative and high pressure sodium bulbs for flowering.
