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The Purpose of Light Fixture Insulation: A Clear Explanation

Opening up a light fixture and finding it stuffed with insulation can be confusing. Like me, you might have been alarmed at first seeing a flammable-looking material in such close quarters with potentially hot light bulbs. Of course, insulation is purposefully fire-resistant, so that, at least, is not an issue.

Searching the internet brings up a few theories as to why insulation is in light fixtures, but there is only one true reason.

Light fixtures have insulation to protect electrical wires from overheating from the heat generated by the bulbs and potentially causing a fire.

Suggested Theories

There are three popular theories for why light fixtures have insulation:

  1. The foil back of the insulation makes the light reflect into the room better.
  2. The insulation stops drafts from around your light fixture.
  3. The insulation prevents the bulbs from heating up the wiring.

Let’s have a look at all three and see which theory is correct and the reasons why this is the only correct one.

Reflection Is Not the Purpose of Insulation

If you have been led to believe that insulation helps the light reflect better into the room, I’m afraid the internet has been lying to you!

The foil backing on insulation that you see when you open the light fixtures is where this theory comes from.

Light fixture with foil and insulation illustration

So, why is this not the right theory? There are four main reasons:

  1. Foil backing is not always a feature of insulation.
  2. If reflection was the goal, why install insulation? Why not just install a reflective surface?
  3. Light fixture reflectors are a separate part that can be added to light fixtures or which are built-in, such as a polished metal or mirror-like finish.
  4. The foil backing will not do the job very well. Reflective light fixture finishes, actual reflectors, light wall/ceiling paint, and mirrors are all going to be much more effective in achieving this goal.

Insulation Not Positioned for Draft Prevention

If you thought theory number two was the correct one, I’m sad to say you are wrong again.

Insulation stuffed into the light fixture does not help prevent a draft.

For one, insulation is installed inside the actual fitting and not around the edges where a draft may come through.

While it may provide some draft protection by filling any gaps in the actual fixture, it is not specifically designed to stop airflow and is unlikely to be airtight.

Drafts can come from a variety of sources, such as gaps in the walls, around windows and doors, and other openings in the building. In order to effectively prevent drafts, it is important to address all potential sources of air infiltration rather than just focusing on the light fixtures.

The Correct Reason: Protecting the Wires

So, the winning theory is theory number three.

Light bulbs, particularly incandescent bulbs, produce heat as a byproduct of their operation. Have you ever touched a light bulb that’s on? You’ll notice they can get quite hot.

This heat is generated by the resistance of the filament inside the bulb as it is heated by an electric current.

This heat is generated by the resistance of the filament inside the bulb as it is heated by an electric current, filament

The heat dissipates into the room, but the light shade surrounding the bulb typically traps some of the heat within the fixture and against the ceiling and wires therein.

The wires that bring electricity to the light bulb also get hot while they are working. This happens because electricity has to work against resistance in the wires, and this resistance makes the wires get hot. This is especially true for bigger light fixtures or fixtures that have longer wires. 

The heat generated by the light bulb can spread to the wires, causing them to overheat. The insulation in the light fixture helps to prevent heat from spreading to the wires and reduces the risk of fire. 

Now, the insulation used in light fixtures is typically made from a non-flammable material such as fiberglass or mineral wool. It would be a bad idea to use cellulose or natural fiber insulation, as these themselves are flammable (although these are treated with fire retardants).

The insulation is not in direct contact with the light bulb but rather is placed inside the light fixture itself.

This means that the insulation creates a barrier between the light bulb and other components in the light fixture. It also helps prevent these components from getting too hot and becoming a fire hazard as well.

Even though the heat from the bulb and wires can still dissipate into the surrounding room and the heat from the wires can still escape through the ceiling, the insulation helps reduce the heat that reaches these areas and improves the overall safety of the light fixture.

Insulation Over the Light Fixture

Insulation is not allowed to be installed over a light fixture because it can create a fire hazard. When insulation is placed over a light fixture, it can trap heat and prevent it from dissipating properly, which can cause the fixture to overheat and potentially start a fire. 

In addition, if the insulation is flammable, it can ignite and spread the fire even more quickly. Therefore, it is important to note that the type of insulation used in a light fixture must be approved and comply with safety standards. 

So, why is insulation allowed inside the fixture? Well, in some cases, it is necessary according to the IRC codes. 

Section E4003.3 states any electrical fixture that has exposed conductive parts, such as the metal casing of a light fixture, must either be connected to a grounding wire or be designed with double insulation to ensure that there is no risk of electric shock if someone comes into contact with it.

Section E4004.8 says if you have non-insulated recessed lights, you need to make sure flammable materials, like wood or other insulation, are at least a ½ inch away.

If this is not possible, you will need recessed lights that are designed to be in contact with insulation without creating a fire hazard (Type IC (Insulation Contact)). 

Amico 5/6 inch 3CCT LED Recessed Lighting 12 Pack, Dimmable, IC & Damp Rated, 12.5W=100W, 950LM Can Lights with Baffle Trim, 3000K/4000K/5000K Selectable, Retrofit Installation - ETL & FCC Certified

The IRC continues on with Section E4004.9, saying if your recessed lights are not Type IC, then any thermal insulation, such as fiberglass or foam must not be installed above or within 3 inches of the light enclosure.

Do LED Bulbs Make Insulation Unnecessary?

Now, you may be thinking, if I have an LED bulb, I shouldn’t need insulation as they generate less heat. However, it is still important to insulate around LED bulbs and light fixtures. 

While LED bulbs produce less heat than traditional incandescent bulbs, electrical wiring and other components in the light fixtures can still generate significant heat. It’s also important to note whether your LEDs are fire-retardant or not. If not, they will need to be insulated as stipulated in the IRC codes.

When looking at online forums, most people don’t suggest removing insulation, even if you are using LEDs for your downlights. If you really want to remove the insulation but still want to be safe, you can purchase a fire-retardant cover like this one from Tenmat (amazon link).

Tenmat FF109-300 One Hour UL Fire Rated Recessed Light Cover, Black; For Solid Wood Joists, Open-web Wood Trusses or I-shaped Wood Joists On Max 16" On Center

So, there really is no point in removing the insulation from light fixtures. Additionally, insulation provides many benefits beyond reducing heat transfer, such as improving energy efficiency and reducing noise transmission

Insulation can help to reduce the amount of noise generated by the light fixture, especially that irritating buzzing noise you generally get from LED bulbs.


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