# How Many Bulbs Do I Need?

If you're building an infrared sauna or otherwise want to experience soothing heat and penetrating near infrared energy, you may be wondering how many bulbs you'll need. In this blog post, we'll provide you some information and resources to help you determine the right number of bulbs for your use.

## Maximum Number of Bulbs

Before discussing how to calculate the number of bulbs you need, we're going to first explain the maximum number of bulbs you can use at one time. You're limited by the capacity of your home's electrical system, which is 15 amps per circuit in most homes. 15 amps allows you to draw 1800 watts of power from one circuit at one time. A home typically has multiple circuits, each of which is comprised of as many as 25 outlets. Circuits generally cover multiple rooms in your home. This means that, while the circuit offers 1800 watts of power, it is unlikely that all 1800 watts will be available to operate your TheraBulbs. The full 1800 watts would be available only if nothing else was operating on the circuit or you installed a dedicated circuit, as is described in our enhanced DIY sauna construction article.

In order to determine the available capacity on the circuit you're going to use to operate your TheraBulbs, first find out what is drawing power from the outlets that are on the same circuit as the one you're going to be using. You can often find this information on the inside of the door to your home's circuit breaker box. If this information is not documented, you'll need to map your home's electrical circuits. Once you know what is drawing power on the circuit, you can deduct its wattage from 1800 to get the total available power. After that, you'll need to divide the available wattage by the wattage of the bulbs you're planning on operating.

**Example**: 1800 watt circuit - 450 watts for a refrigerator = 1350 watts available. 1350 watts / 150 watts = 9. Therefore, you can operate a maximum of nine 150W bulbs at one time on that circuit.

**Maximum Temperature **

If you are trying to determine the number of bulbs needed to raise the temperature of the room a given number of degrees, you'll want to enter the characteristics of the room into a heating calculator. Here's a link to a website that has one such calculator: https://www.calculator.net/btu-calculator.html The second one on the page, General Purpose AC or Heating BTU Calculator, is the one to use.

**Example**: If your room is five feet wide by five feet long, has a ceiling height of nine feet, is well insulated, and you want to raise the temperature in the room 50 degrees, the calculator tells you that you need 720 watts. Since the wattage of TheraBulbs is divisible by 50, look for a combination of bulbs that adds up to 750. This would be five 150W bulbs or three 250W bulbs or two 300W bulbs and one 150W bulb.

## Beam Spread

If you are trying to determine the number of bulbs needed so that you can expose your whole body at once to red light and near infrared energy, you'll need to know the beam spread of each bulb. In this case, fortunately, we've done the math for you. TheraBulbs conform to lighting industry bulb shape and size standards. Our 150W bulbs is type/size R95 and the 250W and 300W bulbs are type/size R40. Each type/size has a different beam spread, which is the technical term for the diameter of the beam of light produced by the bulb at a given distance. Beam spread is determined by the shape of the bulb and the reflectors inside it. Bulb types that have an R in their names are flood type bulbs, which means they have a larger beam spread than other types of bulbs. As a result, the light from a single bulb will spread out quite a bit as the distance from the bulb increases, as shown in the table below.

### Beam Spread vs Irradiance

As previously mentioned, beam spread increases with distance from the bulb. We've provided the beam diameter for all of our incandescent bulbs at .33M - 1M from the bulbs. These are the same distances as the lab-tested irradiance measures for our bulbs.

Irradiance is the technical term for intensity of light. Irradiance can apply to both visible light, which can be seen with the naked eye, and infrared energy, which is not perceptible to the naked eye. Whether the light/energy is visible or not, its irradiance decreases as distance from the source increases. (Think of how a lightbulb seems much brighter when you are beside it than when you are across the room from it.) For this reason, irradiance data always includes the distance from the source, such as .33M, .5M, 1M. Irradiance is measured in milliwatts per centimeter squared(mW/cm2), with larger irradiance numbers indicating more energy available at that distance.

Knowing the irradiance of a red light/near infrared bulb lets a user know how much energy the bulb emits at a given distance. This information can be used to compare two or more brands of bulbs or bulbs with different wattages. It can also be used to determine how close to get to the bulb. While safety dictates that 12 inches / .33M is the minimum distance to maintain from the bulb, irradiance data can help users determine the effects of using the bulb at a greater distance. To learn more about irradiance, read our blog post, Irradiance and Red Light/Near Infrared Bulbs.

You'll note that irradiance decreases with distance from the bulb and beam spread increases. This means that when you're deciding how many bulbs you need, you'll need to evaluate what number of bulbs will give you the most coverage and the highest irradiance.

## Learn More and Save!

If you have questions that we didn't answer here, feel free to contact us at support@therabulb.com. And, when you're ready to purchase your bulbs, take advantage of our sauna owner discount, which gives you 15% off when you purchase four or more bulbs — mixing and matching sizes is welcome. Simply enter the word SAUNA at checkout.