Select Page

After a few beers on Friday night, we got talking about the office lights and where they were on a scale of one to crap. Having had a few by this point I merrily volunteered my skills to answer the question of what we should do, whether to repair them, replace them like for like or put shiny new LED units to save us some money in the long run, so I built a fairly simple model.

I started off with a few concepts for each light:

  • Running Costs (Energy Usage Costs, Carbon Emissions)
  • Installation Costs (Parts + Labour)
  • Lifespan (How frequently the parts will need to be replaced)

I broke it down into some overall values for each light:

  • Cost per kWh (Kilowatt hour)
  • Usage hours per day
  • Usage days per year
  • Number of lights
  • Installation cost per light
  • Percentage of non-renewable energy produced in NZ
  • Kilogram of carbon per kWh (kilowatt hour), based on a rough average over the types of fuel burned in NZ

Some type specific values for each light:

  • Watts per hour
  • Unit price (dollars)
  • Life expectancy (hours)
  • Bulb replacement cost (dollars)
  • Bulbs per unit

Then did my calculations with a couple of things to note:

  • It assumes that all bulbs last their entire lifetime, it doesn’t account for failure rate (reason for steps in the chart below).
  • The cost of ballast replacement doesn’t account for the life of the current bulbs, which will need to be replaced sooner, as they may not be replaced with the ballast. In this case a ‘light’ consists of the bulb which generates the light and the ballast, which is are the electronics that supply electricity to the bulb. Changing to LED lights would require changing both the ballast and the bulbs.
  • Carbon emissions were based on an approximation of 40% renewable energy (sourced from Wikipedia) with an averaged amount of carbon emissions across the types of fuel NZ burns for the remaining 60%, based on the percentage of each.
  • Inflation costs are not accounted for.
  • Potential changes in renewable energy percentage are not accounted for.

I ended up with an approximation of around six years to recoup the costs of fitting an LED light over replacing the unit with another fluorescent fitting. With seven years cost neutral for ballast replacements, although if you account for the earlier failures of the bulbs, then that time frame will reduce.

In the end it comes down to two real questions:

How long do we plan to be in this office? – if we’re in it for the long haul (6+ years) then it makes financial sense. If not then it’s not cost effective.

Light costs over years

How much are you willing to spend to reduce your carbon footprint? If the answer is less than the additional cost, then stick with the fluorescent lights, but if you feel the price difference is worth the cost of going green … er then it might be time to get rid of those old school lights.

Carbon Emissions

I know what my choice would be.

Keep exploring! Daniel.

%d bloggers like this: