Lighting, in allowing people to be productive outside daylight hours, is one of the most important applications of electricity. Given its importance, it’s pretty interesting that for most of the world, the mainstay technology – the incandescent bulb – has hardly changed for a hundred years. What’s more, incandescent bulbs are incredibly inefficient, converting only about 2% of the energy to light, with the rest wasted as heat. This is now finally changing, with country after country banning incandescent bulbs in favor of more efficient lighting types. It’s about time, but for many it also raises another question: what lighting type does one switch to? What is the best? The primary drive is towards compact fluorescent bulbs, but is this appropriate?
By “best” I mean the cheapest option that is versatile enough to create an all-around comfortable and functional indoor lighting environment. Cheapest off-the-shelf price is misleading at best so I like to instead look at the total cost of ownership-type of figures. So, let’s take a look at the long-term (25yrs) total costs (bulbs + electricity used) for different lighting types.
CFL = Compact Fluorescent lamps, LED = Light-Emitting Diodes. Assumptions used to make the above chart: average usage 4hrs/day, 365 days per year. Bulb prices from http://lightingpro.com.au/, http://www.lightbulbsdirect.com/ and http://www.lc-led.com/, electricity priced at constant $0.20/kWh, lumen efficiencies as quoted by the manufacturer / vendor or averaged from figures at http://en.wikipedia.org/wiki/Luminous_efficacy where not available. Bulb prices averaged per year based on expected lifetime, future bulb purchases assumed at today’s prices. Includes only “mainstream” technologies suitable for residential indoor lighting; gas discharge and arc lamps have been intentionally omitted.
Based on this, standard (large) fluorescent tubes typically used in commercial buildings are by far the most cost-effective means of lighting a space. Residential houses usually aren’t designed to take advantage of this form of lighting (though nothing says they couldn’t be) as the primary lighting source. If one looks at the graph further, you will see that LED lights have roughly equivalent electricity costs to fluorescent lamps. Once the LED lamp costs come down – and they are continuously decreasing, unlike the mature technology of fluorescent tubes that are already cheap – LED lamps are likely to become the #1 choice in the next few years.
As the chart assumes unchanged electricity prices – which obviously is not going to be the case – it makes sense to look for the lighting type with the lowest possible “electricity cost” component. This would also point towards LED lights and fluorescents, the Top 2 in total cost as well.
In researching this, there were a couple of surprises:
- Even though the LED light efficiencies are an order magnitude more than with incandescent bulbs, their efficiency is still only a maximum of 20% or so. Considering my trusty old “chili-growing” HPS (high-pressure sodium) lamp matched that efficiency 10 years ago, I’m a bit disappointed.
- I was also somewhat surprised to discover that LED lamps are already, even at their high unit prices (as much as $80 for a “standard” lamp), very competitive. Given that long fluorescent tubes are not always an easy retrofit and not applicable everywhere, LED lamps already lead all other lighting types in terms of total costs. As residential lighting is a very new application for LEDs, this is surprising.
One should note that as this was a pure efficiency / cost calculation, no externalities were taken into account. For example, CFL tubes are hazardous waste and still take a while to reach full luminosity when turned on – both clear disadvantages.
Another major negative externality has to do with halogen bulbs. I used to like halogen bulbs. I liked their compact size, relatively long lifetime (5x of incandescent bulbs) and even the modestly higher efficiency compared to incandescent. And when recessed into the ceiling, as many modern Australian houses do, they look good – and therein, it turns out, lies a major problem. Halogen lamps get exceedingly hot, meaning they need plenty of ventilation – open air around them. This means that large holes need to be cut through the ceiling insulation, often dramatically lowering the R-value of the insulation. This is a big “no no” and makes recessed halogen lighting a very bad choice, unless one uses an expensive dual ceiling construction.
In conclusion, I thought LED lamps were the future #1 choice for residential lighting. Instead it appears that for many, if not most, homes they are the #1 choice today, even at the high initial costs.