color of a light source entails a complicated relationship of different
factors, that are important in determining the right light source for
your garden. The advantage of Metal Halide lamps is that they provide
high-quality, crisp white light in a variety of different color
temperatures that meet the needs of many different users.
Correlated Color Temperature(CCT)
The first factor in choosing a color of lamp is to determine
whether you need a warm or cool light source. The CCT, expressed in
Kelvin degrees, relates to actual thermal temperature. If you've ever
seen a piece of metal being heated, you know that as the metal gets
hotter, it's color changes. The CCT rating of HID and flourescent light
sources indicate how warm or cool the light source is. For instance a
lamp with a CCT of 2700 Kelvin is considered warm; with a CCT of 4200
Kelvin is considered neutral; and one of 6000 Kelvin is considered
Spectral Energy Distribution
When you look at a light source, you perceive seeing a single
color, but you are actually seeing thousands of hues. The combinations
of different wavelengths of light make up the color we see. The
relative intensity of the various wavelengths are used to determine a
light source's Color Rendering Index(CRI).
Color Rendering Index(CRI)
The CRI is an indication of a lamps ability to show individual
colors relative to a standard. This value is determined from a
comparison of the lamp's spectral distribution compared to a black body
at the same color temperature. Light sources, such as metal halide
lamps, are rated with a CCT; however, CCT does not provide any
information on the quality of the color. For this, a CRI is also
necessary. In general, the higher the CRI rating of a lamp, the better
the different colors will show.
5K - 7K Kelvin: Strong Blue Light
Promotes bushy growth. Ideal for rapid growth phase of plants.
Greatly enhances all-around plant growth when used with super
high output, high pressure sodium or 3K warm metal halide lamps.
4.2K - 4200 Kelvin: Cool white Flourescents
Can be used as supplimental blue lighting when used with a 3K
4K - 4000 Kelvin: Neutral Metal Halide
Best single source for plant growth, producing shorter, bushier
growth than 3700 Kelvin and color rendition. Used in general
3.7K - 3700 Kelvin: Softer Metal Halide(coated)
This coated lamp is used in general plant lighting and for more
rapid growth than 4000 Kelvin produces.
3K - 3200 Kelvin: Warm Metal Halide
Highest photosynthetically active radiation (PAR) value of all HID
lighting for all phases of plant growth. PAR watts account for the
nutritional value of light and are a direct measure of the light
energy available for photosythesis.
2.7K - 2700 Kelvin: High Pressure Sodium Lamps
Redder color mix, used for propagation, blooming, supplemental