Controlled Environment Agriculture

Luminaire Comparison

This paper begins with a review of supplemental lighting terminology and luminaire components. The luminaire component that is responsible for the greatest loss in quantum efficiency is the reflector and many properties of reflectors are discussed. The purpose of this exercise was to quantify the difference in photosynthetically active radiation (PAR – the portion of the electromagnetic spectrum that plants actually use) and  PAR distribution patterns that exist in the nine most common commercial supplemental luminaires on the market. The most efficient (or efficacious, read the paper to learn the difference) supplemental lighting system are high pressure sodium (HPS) luminaires which are a type of high intensity discharge (HID) luminaires. The same 400W lamp (aka bulb) was used to test the PAR output and distribution of the nine luminaires. The following are useful results and calculations from the report:

  • Average wattage of the entire luminaire (including ballast)
  • Efficacies of each luminaire in mol PAR per kWh
  • Number of luminaires of each model it would require to provide supplemental PAR at an intensity of 50 umol m-2 s-1 for an approximately one acre greenhouse in a grid pattern (ex. 676/acre for most efficacious and 840 per acre for the least efficacious)
  • Uniformity of the supplemental light if the luminaires were arranged in different patterns to reduce ‘edge effects’ and increase uniformity. This example demonstrated that the variability of the light distribution could be reduced by ½ if the arrangement of the luminaires was changed from a grid to various patterns.