Seedling Care – Artificial Light Sources

To compare sunlight with other artificial sources of light we need to outline the differences between them. Some of these differences are not obvious without using optical tools. Also, our eyes can sometimes deceive us when viewing one light source compared to another since they do not respond equally to different colors at equal intensity.

The first obvious difference between sunlight and artificial light is the light intensity. Full sunlight is very bright. Artificial sources can be as bright but it takes a fair amount of power to do this.

Not so obvious is the spectral content of the light source. There are very big differences here. And there is a lot of controversy over these differences. Some insist that not only does the light intensity have to approach sunlight’s intensity, but the spectral content must match as well. Others claim that although this may be true for some flowering plants, it does not apply to seedlings.

If you pass sunlight through a prism you will get a rainbow of colors sort of like the image on the right. Sunlight is a mixture of all colors of visible light (and invisible light as well). The prism bends different colors of light different amounts which separates the sunlight into a band of colors. Note that with sunlight there is an even distribution of energy at all colors.

If light from a cool white fluorescent lamp is passed through the same prism the rainbow looks quite different. The image on the left is an artists rendition of what it looks like (as best as I could do with my limited experience with paint shop pro). Note that the light energy is not evenly distributed but is instead concentrated in narrow “lines”. There is some broad rainbow like energy but it is not as wide as sunlight and much much dimmer.

Other artificial light sources look completely different from either the cool white or sunlight spectrums.

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