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Understanding Lighting Color Temperature

Choosing the right lighting color temperature can be challenging. In this article, we'll discuss how to select the appropriate color temperature for various applications, such as residential, commercial, and garden settings. We'll cover correlated color temperature (CCT), spectral energy distribution, and color rendering index (CRI).

Correlated Color Temperature (CCT)​

CCT is a measurement that indicates how warm or cool a light source appears, expressed in Kelvin degrees. A lamp with a CCT of 2700 Kelvin is considered warm, while one with a CCT of 4200 Kelvin is neutral, and 6000 Kelvin is cool. Determining if you need a warm or cool light source will help you choose the right lamp for your needs.

Spectral Energy Distribution​

When looking at a light source, we perceive a single color, but it's actually made up of thousands of hues. These combinations of different wavelengths make up the color we see. The relative intensity of these wavelengths is used to determine a light source's CRI.

Color Rendering Index (CRI)​

CRI indicates a lamp's ability to accurately render individual colors relative to a standard. It's determined by comparing the lamp's spectral distribution to a black body at the same color temperature. While CCT provides information about a lamp's warmth or coolness, CRI is essential for understanding the quality of the color. Generally, the higher the CRI rating, the better the colors will appear.

Choosing Lighting for Your Garden​

Metal halide lamps are advantageous for gardens due to their high-quality, crisp white light at various color temperatures. Here's a guide to help you choose the right lamp for your garden:

  • 5K - 7K Kelvin: Strong blue light, ideal for rapid plant growth and bushy growth. Works best when combined with high-pressure sodium or 3K warm metal halide lamps.
  • 4.2K - 4200 Kelvin: Cool white fluorescents, suitable as supplemental blue lighting when used with 3K sources.
  • 4K - 4000 Kelvin: Neutral metal halide, the best single source for plant growth, producing shorter, bushier growth than 3700 Kelvin and good color rendition.
  • 3.7K - 3700 Kelvin: Softer metal halide (coated), used for general plant lighting and promoting faster growth than 4000 Kelvin.
  • 3K - 3200 Kelvin: Warm metal halide, with the highest photosynthetically active radiation (PAR) value, ideal for all phases of plant growth.
  • 2.7K - 2700 Kelvin: High-pressure sodium lamps, with a redder color mix, suitable for propagation, blooming, and supplemental greenhouse lighting.
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  • mmmdankbuds420
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Haven't seen a thread yet explaining color temps. Informative.
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