Do Incandescent Bulbs Heat Up A Room?

All across the globe, incandescent bulbs are gradually being phased out. You see, these tungsten filament luminaires are incredibly inefficient.

Approximately 90% of an incandescent bulbs energy is wasted as heat, with a measly 10% being used to create light. In contrast, LED bulbs produce 90% light and only 10% heat.

In recent years, however, defenders of incandescent bulbs have argued that their heat can be valuable. That is, the heat warms up the surrounding room, which in turn saves on energy costs.

So is it true?

Incandescent bulbs can increase the temperature of a room, but only by one or two degrees. This depends on a variety of factors, including the room’s dimensions, the bulbs wattage, and how well insulated the room is.

Whether you’re for or against incandescent bulbs, this is undoubtedly a contentious area.

If you’re eager to hear my take, then keep reading. In this article, I’ll cover everything from how much heat an incandescent bulb produces and how many bulbs it would take to heat a small bedroom. Enjoy!

Can You Heat Up The Room With Incandescent Bulbs?

Before I jump into the heat debate, let’s look at how incandescent bulbs work.

Incandescent bulbs produce light by heating a small metal filament until it glows. Essentially, the filament atoms do not know how to handle their newfound electrical energy, so they release it as photons (light).

Understandably, this process requires a lot of heat. If the filament is not hot enough, no photons will be released.

This immense amount of heat can warm up the surrounding atmosphere, much like a radiator. This is why incandescent bulbs are often used in things like incubators and reptile habitats.

So back to the question at hand, yes, an incandescent bulb can heat up a room. But whether you should use incandescent bulbs as a heat source is another question.

In any case, the temperature increase produced by an incandescent bulb will be relatively minor. It may help to lower your heating bill a tiny bit, but there are much better ways to keep yourself warm.

Furthermore, an incandescent bulbs ability to increase room temperature is affected by several variables:

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  • The bulb’s wattage.
  • The size of the room – Incandescent bulbs will heat small rooms better than big rooms.
  • The room’s ventilation – Rooms with good ventilation will be harder to heat.
  • The location of the room – Heat rises, so attic rooms will be more susceptible.
  • The number, size, and thickness of any windows.
  • The color of the walls.
  • The outside temperature.

How Much Heat Does A 60W Incandescent Bulb Produce?

high temperature

For light to be produced, the filament inside an incandescent bulb must be heated to a whopping 4000°F. So what effect does this have on overall room temperature?

Well, an incandescent bulb emits 90% of its energy as heat and 10% as light. Therefore, a 60W bulb emits 54 watts of heat and 6 watts of light.

But watts represent the power consumption of the bulb. Thermal energy (heat) is better quantified in Joules (J).

One watt is equal to one joule per second. So a 60-watt bulb uses 60 joules of energy per second.

Therefore, using a 60-watt bulb for 60 seconds produces 3,600 joules of heat energy.

Are you following? Good, then let’s carry on.

Let’s imagine your room is 15-foot x 20-foot x 10-foot. This equals 3000 cubic feet or 84.95 cubic meters.

The volume of air in the room is 84.95 cubic meters x 1.2kg/m3. This equals 101.94kJ.

To increase the temperature of a substance by one degree, you need to know its specific heat. The specific heat for air is approximately 1 kJ / K*kg.

So it would take approximately 101.94 kJ of energy to heat the room by 1 degree.

The 60-watt incandescent bulb produces 3,600 joules of energy per minute. Therefore, it would take 28 minutes (102,000 kJ / 3600 J) to increase the room temperature by 1 degree.

This of course is under the condition that no one enters the room and heat has nowhere to escape.

How Many Bulbs Would You Need To Heat A Small Bedroom?

If you’re looking for a cheap way to heat your home, you may be considering light bulbs. After all, purchasing 10 x 100-watt incandescent bulbs is less expensive than buying one 1000-watt heater.

But let’s put this theory to the test.

It’s widely accepted that optimal room temperature is between 68 and 72°F. For this exercise, let’s assume that the room is currently 50°F. So room temperature needs to be increased by at least 18°F.

Using the calculations from earlier, it would take 1 x 60-watt incandescent bulb approximately 504 minutes (8.4 hours) to increase the temperature by 18°F. Alternatively, it would take 15 x 60-watt bulbs 34 minutes to increase the room temperature by 18°F.

Of course, this is dependent on the size of the room and the amount of ventilation.

With these numbers, incandescent bulbs may seem like an excellent alternative to traditional heating. But this is not true.

You see, heat rises upwards. But most light bulbs are positioned high up on the ceiling. Essentially, this means that the upper portion of your room will be nice and warm, but the lower half will remain cold because hot air cannot float downwards.

This is very impractical since humans sit on the floor… not the ceiling!

Do Fluorescent Bulbs Increase Room Temperature?

As I mentioned in the introduction, this debate is somewhat futile since incandescent bulbs have been discontinued. Nevertheless, if you’re a lover of incandescents, you’re probably wondering whether there’s an alternative.

The answer: not exactly.

Fluorescent bulbs produce light through the process of fluorescence.

In simple terms, electrical current passes through the glass bulb and excites mercury gas vapor.

In turn, this produces ultraviolet light, which is converted to visible light by a phosphorous coating on the inside of the lamp.

As you can see, this process hardly involves heat. So it comes as no surprise that fluorescent bulbs are much more efficient than incandescents. That is, 70% of their energy is used to produce light, and only 30% produces heat.

Ultimately, this means that the impact of fluorescent bulbs on room temperature will be tiny. I’m talking 1/10th of a degree!

Final Words

Hopefully, this article has proven that you shouldn’t need to switch your standard household heaters to incandescent bulbs anytime soon.

Theoretically speaking, the heat produced by an incandescent bulb can be useful in the home. But in reality, it’s far too minuscule and erratic to be of any real value.

My personal opinion is that energy-efficient LEDs are an all-round better solution. Let’s leave heating your home to the heaters.

Have you tried heating your home with incandescent bulbs? Do you agree that these inefficient light sources belong in the past? I’d love to hear your opinions.

2 thoughts on “Do Incandescent Bulbs Heat Up A Room?”

    • Hi Vivek,

      I remember when I was a kid I had this little lamp with incandescent bulb inside and whenever I turned it off, I could feel the heat for a while.

      Thanks for sharing,
      Eugen

      Reply

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