Calculating Light Energy Costs

Here is a simple formula for calculating the energy costs of your light.

Information to gather:

STEPEXAMPLE
1. Get your energy costs in kW/hr from your utility bill. (KW)
$0.12
2. Fixture Qty (FQ)30
3. Bulb Wattage (BW) Use 1 for 1000W, 0.6 for 600W, and 0.4 for 400W.6
4. Hour lights run per day (HR)16

FORMULA

BW x KW x HR x FQ  = Cost to run fixtures per day
0.6 x $0.12 x 16 x 30 = $34.56 / Day
Multiply by the number of days in a month to get the monthly rate

Procedures for Replacing a Lamp

We recommend following the steps below when replacing a lamp:

  1. Disconnect power to the ballast. Removing/installing a lamp into a powered ballast can cause ballast and/or lamp failure, and is a safety hazard. Always remove power from the ballast before performing any maintenance.
  2. Remove and replace the suspected bad lamp with a known working lamp.
  3. If the lamp is cool, it should start immediately. If it does not ignite, allow 2 minutes for the ballast to attempt to restrike the lamp.
  4. If the lamp does not ignite, power down the ballast and attempt another known working lamp. This reduces the possibility of a component-level incompatibility due to manufacturing tolerances of the lamp and/or ballast.
  5. If both lamps fail to ignite, the assumption is that the ballast has failed and requires replacement.

NOTES:

  • Never remove a lamp when a ballast is receiving power.
  • Never have a powered ballast without a lamp inserted in the socket.

Bench and Bed Layout is Important

Most light plans focus on average light levels and acceptable uniformity in the greenhouse. These figures can change significantly based on the spacing between lights and distance of the lights from the plant canopy. If general information such as width and length of the greenhouse is the only information provided to the designer, you may receive varying light plans and results.

To help develop proper lighting plans, it is important that you include the bench or bed layout. Providing a bench or bed layout enables the lighting designer to concentrate the light on the essential growing areas rather than wide center walkways or work areas in the back of the greenhouse. The information needs to provide other details such a bench orientation or distance from the walls or aisle space as these details can vary design calculations and results.

More importantly, if a detailed layout includes a bench or bed design, it can save the grower money. These savings can be achieved by improving light uniformity resulting in consistent growth of your plants and in most cases you will see a reduction in the number of fixtures for your project.