This is the final article in our four-part series about indoor plant lighting. You can also read the first, second, and third articles.
You may see two other details provided in lamp specifications aside from the terms introduced in my last installment. They are not critical factors but can influence your satisfaction with how the lights look by themselves, and how plants, decorative pots, and other objects look underneath them.
The appearance of plants under the lights is not only important for aesthetics, like seeing the true colors of blooms, but also for detecting leaf discoloration, which can be a key symptom of malnutrition, light stress, or pest or disease damage.
Color Rendering Index (CRI)
While this doesn’t affect actual light intensity, it does impact our perception of how colors will look under a light and is a matter of personal preference.
On a scale of 0 to 100, the higher the CRI value a lamp has, the more accurate the colors will look compared to viewing in natural light. At the low end of the scale, colors are lackluster (desaturated) and less distinguishable from each other. Since incandescent, fluorescent, and LED lights all produce light by different means, they have different CRI ranges, though improvements in technology are closing this gap. Ideal ratings are in the 80s and above, with the 90s considered “high CRI.”
This is the third in our four-part series of articles about indoor lighting for plants. You can also read the first, second, and fourth articles.
Artificial light sources come in several forms, all relatively easy to acquire. Costs can vary wildly, and some are more electrically efficient than others. The variety of available options allows you to customize setups to your needs and the preferences of your plants. Before you dive into an overwhelming list of web search results, here are traits of the basic categories:
Light-Emitting Diode (LED)
best energy-efficiency in terms of light produced per watt consumed (especially if the light has the ideal spectrum)
coolest to the touch except for high-powered units, which usually have small built-in cooling fans
can be expensive for high-quality fixtures, though costs are decreasing
light output does not dim significantly over time, though diodes do have a finite lifespan
reach full brightness immediately or very quickly when turned on
diodes can either be exposed or under a frosted or textured cover to help diffuse the light
diodes are directional, meaning they don’t emit light in every direction the way a fluorescent tube does, so reflectors aren’t usually needed
more even light output from one edge of the fixture to the other
can be round like a spotlight (with a cluster of diodes) or straight strips (or strips inside a tube) with one or more rows of diodes
some replacement “tubes” can be used in place of fluorescent tubes in a fluorescent fixture, but you must check with the fixture’s manufacturer for compatibility as mixing components is a matter of electrical safety