1. Color Rendering Index (CRI) is similar to our sun.
CRI measures the ability of a light source to show an objects true colors in comparison to a natural light source.
HPS Bulb CRI = 20-30
CMH Bulb CRI = 90-92
This makes it only 8 points off from the most natural light source available which is our sun.
As you can see the apple with the CRI of 100 looks the most natural due to the light source.
What advantage does that bring?
This means you are providing your plants with UV-A, UV-B, UV-C, and IR spectrum similar to the sun, which is very beneficial to your plants trichome development.
2. Low heat output and electrical consumption
Lower wattage means you'll save some money on your electricity bill, but it also means you will generate less heat.
1W = 4 BTU's
This means one 315W CMH system will give off 1,260 BTU's compared to a 600W HID which gives off 2,400 BTU's. That's about double the BTU's.
Having a cooler room will lead to you using your A/C less and saving even more on electricity.
3. Consistent PAR Value
*image provided by growace.com
As you can see there is a consistent spread of light across the board. There is a dramatic increase in PAR value between the 630W and 315W as the 630W CMH system utilizes two 315W bulbs. There is certain scenario's where using the 315W would be more beneficial then the 630W and vice versa.
4. CMH Bulbs last longer
CMH bulbs have a longer life span compared to HID bulbs or fluorescent bulbs. The general guideline is to replace your HPS or MH bulb after 10,000 hours of running. On average, CMH can last over 20,000 hours which is double! To add to that, they still keep 80% of its initial output spectrum after 20,000 hours. MH & HPS bulbs deteriorate at a much faster rate.
CMH bulbs last much longer than other HID or fluorescent bulbs. The standard rule of thumb for MH or HPS bulbs is to replace them after 10,000 hours of use. Good CMH bulbs last over 20,000 hours. Moreover, they still retain 80% or more of their initial output after 20,000 hours. HPS and MH bulbs deteriorate much more quickly.
5. Full spectrum bulb
Using the wavelength graphs as a reference you'll notice that the CMH has a few extra features compared the the HPS bulb. The main difference is that the CMH bulb provides a complete spectrum across the graph as well as UV spectrum to help with trichome development.
As you can see the HPS bulbs are focused at the red spectrum of the graph which is great for flowering, but provides very little benefits to the vegging stage.
The 3100K CMH bulb can be used as a full spectrum bulb due to its wide arsenal of spectrum it releases. We recommend this bulb from clones/seedlings to the flowering stage.
The 4200K CMH bulb has a light spectrum that is more focused on the vegging stage. You may use this bulb for flowering but the 3100K will provide you with better results.
If you have any questions or anything to add please leave a comment below.