For more than a decade we have all been lectured on the virtues of changing lighting technology. The standard, tungsten (incandescent) lighting has been challenged by compact fluorescent lights (CFLs) and bulbs based on light emitting diodes (LEDs). Here is a typical, effusive projection:
CFLs are four times more efficient than standard, incandescent bulbs and last nine to thirteen times as long. If everyone bought just one CFL and replaced their old standard bulb, America would save $8 billion in energy costs, prevent the burning of 30 million pounds of coal, and save greenhouse gas emissions equal to two million cars. Convert all the bulbs and the savings would be in the tens of billions of dollars.
The US government Energy Star program makes similar claims:
ENERGY STAR estimates that if efficient lighting were used throughout the country, the nation's annual demand for electricity would be cut by more than 10%. This would save ratepayers nearly $17 billion in utility bills.
Sounds good, but should there be a comprehensive ban on incandescent lighting? The short answer is, "not necessarily". In fact, they make little sense in a cool climate, either from an energy conservation, environmental or consumer cost standpoint. Ironically, the movement to ban incandescent bulbs is, in fact, in limbo as this is being written. The restrictions were to go into effect for all US states on January 1, 2020.
But in October 2019, the US Department on Energy (USDOE) decided that the regulatory target--a so-called General Service Lamp (GSL)-- was not clearly-enough defined and, in effect, stopped the federal ban on incandescent bulbs. State and local regulation of the GSLs is in limbo, with some states already restricting incandescents and others still planing to do so. Some of these parties sued the USDOE, and the case is currently in the Second Circuit Court. This makes this update timely.
The Forgotten Physics
A 60 watt incandescent bulb does, indeed, use about four times the energy to produce roughly equivalent illumination, in lumens, of a compact fluorescent (CFL) or an LED bulb. As the table below indicates, the lumens per watt of household size bulbs shows that a CFL provides about 40 more lumens and an LED 50 more lumens per watt. Put differently, approximately 75 percent of the power consumed by the incandescent bulb does not produce light, relative to the two other bulb technologies.
However, contrary to the simplistic logic that energy that does not provide lighting is “wasted”, physics tells us that energy is conserved and does not simply disappear. In particular, virtually all of the “extra energy” that is used by an incandescent bulb is dissipated as infrared radiation or convection heat.
In other words, the incandescent light bulb is heating--as well as lighting-- the room. Thus, if the lighting is in a space that must be heated, whether or not this energy lost is a "waste" or not depends upon the climate and heating conditions. If the house is heated, by a gas or electric furnace, the excess heat produced by the light bulb reduces the net demand on these heating systems. This is called the Heat Replacement Effect.
Since three quarters of the energy of an incandescent bulb is available to replace the central heating energy, the economics of this effect can be large, even considering the higher number of incandescent bulbs required over the LEDs. Over the 25,000 hour life of an alternate, cold LED lighting system, for example, the heat energy produced by the incandescent bulb (45 watts per hour) has a value of about $170 at 15 cents per kilowatt hour (assuming that to be the cost of space heating energy. This is more than enough to eliminate the higher total cost of the incandescent.
Thus, in cold and mild climates, at least, there may be no effect on either the cost of electricity to the consumer, or the amount of greenhouse gasses emitted in the production of the electricity used. Indeed, since high latitude climates also are darker and require lighting, the incandescent bulb may be an effective way to deliver warmth closer to the user of the lighting system.
On balance, in cool climates where buildings are heated during low-light seasons of the year, it is not at all obvious that a blanket policy of banning incandescent bulbs makes either economic or environmental sense. They may make sense in regions where additional air conditioning load would be required to offset the incandescent bulbs' heat, but those of us in the coastal northwest should think twice.
Sources:
Shahzad, K. et al., (2015). Comparative Life Cycle Analysis of Different Lighting Devices, Chemical Engineeering Transactions, VOL. 45l
The Heat Replacement Effect, UK Market Transformation Programme, BNX05, Updated: 19/09/2007, www.mtprog.com
Scott Anderson, A state by state look at light bulb bans as of 6/30/21. https://insights.regencylighting.com/state-light-bulb-bans
