Using Light to Enhance Blooming Poinsettias

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Using Light to Enhance Blooming Poinsettias

The color of poinsettia bracts is truest and most brilliant when seen in natural light. While poinsettias grow under natural sunlight conditions, we seldom expose them to natural light in the market chain. In the consumer’s home, poinsettias are under interior lighting, however, the quality of home lighting is often superior to light used in the market. Light enhances or degrades bract color depending on the light source used to display poinsettias.

Light intensity and light quality are two important factors for poinsettia consumer satisfaction. Light intensity is the brightness of the amount of energy falling on the poinsettia. Poinsettias need a minimum amount of light energy to maintain their living processes. When the light intensity falls below this level the plants deteriorate, the leaves fall off and there is a reduction in consumer satisfaction.

The minimum interior light intensity for plant maintenance differs among poinsettia cultivars. For most of the medium green leafed cultivars like Enduring the minimum level is above 100 foot-candles (1076 lux) for eight hours each day. For the dark leafed cultivars like Prestige or Jubilee  the minimum level is little less than 100 but more than 75 foot-candles (807 lux). By comparison, a typical level for home interiors is 50-75 foot-candles (538 to 807 lux), not enough light to sustain blooming poinsettias for more than 3 to 4 weeks. Placing poinsettias near windows during daylight hours for additional light exposure sustains them for longer periods of time. Avoid direct sunlight, however, which may over-heat and burn the plants.

Light quality refers to the balance of colors emitted from a light source. Sunlight emits all colors of the rainbow plus invisible ultraviolet and far-red energy. Electric lamps emit most of these colors, but in different proportions than sunlight. Incandescent lamps, such as the common light bulb, emit a higher ratio of red to blue light compared to cool white fluorescent tubes that emit higher ratios of blue light. Lamps that emit higher ratios of red light enhance the poinsettia bract color. Under blue light, red bracts have a dull bluish-red appearance and look old.

Most retail stores use cool white fluorescent tubes because they are more energy efficient. Many large buildings, like exhibition halls, use mercury vapor lamps. Unfortunately, these light sources drastically dull bract colors.

For best bract color when displaying poinsettias, use incandescent or color corrected lamps with a high ratio of red to blue light. Use these as supplemental spot lights to enhance the appearance of poinsettias that are for sale. At least, provide good quality light for red cultivars. Pink, marble, peppermint, white and yellow colors do not change as severely under poor quality lighting. Poinsettias displayed under good quality light are representative of the colors consumers can expect in the home.

If you are not displaying blooming poinsettias, you can pass this information on to your customers, or use it as a marketing tool.

DO USE DO NOT USE
Lamps which reflect the true color of poinsettias: 

  • Incandescent light bulbs
  • Incandescent spot lights
  • Color corrected fluorescent tubes e.g. incandescent fluorescent
  • High pressure sodium vapor lamps
Lamps which dull the appearance of poinsettias with blue light: 

  • Cool white fluorescent
  • Warm white fluorescent
  • High pressure mercury vapor

 

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