How Big is Full Body Red Light Therapy? Total Joules Dosing.
How much coverage do you need for full-body red light therapy?
The question seems to answer itself. You need to cover 100% of your body for full body red light therapy.
What happens if you only cover 90% of your body? Is that no longer Full-Body Red Light Therapy? Have you suddenly forsaken all of the potential benefits that can only be gotten with 100% coverage?
What about only 80%, 60%, or 50% of body coverage? Is that too low for "full body" benefits? Do you get more benefits from larger devices? How big is the optimal size of a red light therapy device?
If you buy 2 modular devices, do you double your benefits compared to only 1? If you buy 4 and make a whole wall of light, have you quadrupled your benefits? How do we quantify the additional benefits of larger devices?
Or, as the marketing slogan often goes... since it is falsely presumed you need 100% of every crevasse of your skin to be engulfed in light - larger devices will save valuable time in treatments.
Summary - Using Total Joules for Full Body Dosing
Full Body Red Light therapy isn't merely covering 100% of the skin with light, as that ignores all concepts of dosing in favor of optimizing profits by selling oversized devices.
The typical "dose" is referred to as J/cm^2 (Joules per Centimeter Squared).
However, many studies and scientists will prefer to use Total Joules for proper dosing.
The J/cm^2 multiplied by the treatment area (cm^2) of your device gives you the Total Joules dosage.
Full Body Red Light therapy typically delivers tens of thousands (10,000's) or even hundreds of thousands (100,000's) of Total Joules.
Smaller targeted areas do well with several hundred (100's) to several thousand (1,000's) Total Joules.
Using J/cm^2 only gives a small piece of the puzzle for dosing, where Total Joules will play a bigger role in the future for proper dosing of large devices.
Non-contact full-body light therapy is a systemic treatment and not a deep penetrating direct treatment. With that, we can appreciate the proper way of dosing is with the systemic mechanisms based on Total Joules.
As long as we get sufficient Total Joules from a reasonably sized "body-light" device, we should expect to get full-body benefits. Too much Total Joules could lead to a biphasic dose response.
Full-body systemic benefits are often gotten in studies by half-body sized devices covering one side of the torso, with minimum dosing ranging from a few thousand joules to tens of thousands of joules.
What is Full Body Red Light Therapy?
The original commercial "full body" LED panels were only about 3 feet tall (36 inches, 91cm) by 9 inches wide (23cm). This only covers the torso of an average sized adult male.
According to Bionumbers Harvard, the average adult skin surface area is 18,000cm^2 for males and 16,000cm^2 for females. The LED Panel described above is 91cm x 23cm - so about 2,093 cm^2.
That coverage percentage is only 11% of the body for males and 13% for females! If they double their time and rotate to the back, that is only 22-26% coverage.
How could those original panels even produce any full-body effects? Why were they so effective and popular?
Did they inadvertently prove that full-body light therapy can be achieved by only covering a relatively small percentage of the skin? Yes.
In context, remember that a laser spot size typically used in Low Level Laser Therapy (LLLT) is 0.2 cm^2. Yes, two tenths of a centimeter squared. So 0.2 divided by the male human surface area of 18,000 is 0.001% coverage of the body. How could Cold Laser Therapy be so amazingly effective with such a small coverage area?
We can appreciate that even 11% of body coverage with a 3 foot LED panel is already tremendously bigger than 0.001% body coverage with a laser. Which becomes problematic when some brands want to use the intensity of a small laser on a whole body. Where the opposite it generally true, the larger the device, the more prudent it is to reduce the intensity.
Total Joules versus J/cm^2?
What are Total Joules?
The Energy Density (J/cm^2) is the amount of energy delivered to a unit of area. But for most situations, it is more important to know the total energy (Joules) delivered to a system.
It takes about 165,000 Joules of Energy to boil a 500ml mug of water from room temperature. We wouldn't use J/cm^2 to understand the thermodynamics of this situation, we need to know the total energy delivered to the system.
The Density of an object is the Mass divided by its Volume. Rarely do we describe to objects by their Density as that is irrelevant for most situations, we refer to them by their actual Mass or Weight.
Similarly, only talking about Energy Density (J/cm^2) will mask the true dosing of Total Joules. In many ways the Total Energy is more relevant than just the Energy Density (J/cm^2).
If you know the Energy Density (J/cm^2) and the Size (cm^2) of your treatment, you can calculate the Total Joules through simple multiplication.
Proper Dosing With Full Body Red with Total Joules
When asked about dosing of full-body devices, Dr. Hamblin will often bring up the Total Joules.
In an interview with Dr. Hamblin, this is what he says about dosing:
"Dr. Michael Hamblin: It’s a big area. Yeah, I think a few thousand joules is what you want from a photobiomodulation treatment. If it’s only a few hundred joules, it’s probably not enough to do anything unless it’s very carefully targeted to specific areas of the body. For a typical photobiomodulation session on the brain, three thousand joules is about right."
So according to Dr. Hamblin, a typical treatment should be at least a few thousand Total Joules. For targeted treatments the Total Joules could be a few hundred.
As well he notes that 10-20 mW/cm^2 is "high" for full-body light therapy, since that can easily deliver a high amount of Total Joules to the whole body. Which is why it is prudent to use lower intensities for full-body coverage devices.
In another interview between Dr. Hamblin and Joovv, he also reiterates the importance of considering Total Joules for dosing full-body devices, and that Thousands of Joules (1,000's) is a good dose.
This is reinforced by yet another interview with Dr. Hamblin on the CytoLED website. In it, he now says that a typical full-body dose is on the scale of 10,000's (tens of thousands) of Total Joules, and even around 100,000's (one hundred thousand) Total Joules.
So notice that according to Dr. Hamblin, the dose of "full body" red light therapy doesn't seem to matter if it is actually covering 100% of the body. He seemingly changes the topic to talk about Total Joules when asked about dosing large devices.
Since full-body light therapy is a systemic (indirect) treatment anyway, it is more important to consider the Total Joules delivered to the skin, and not actually engulfing all the skin in light.
What Are The Benefits of Full Body Red Light Therapy?
All we need to do is define what benefits to expect from "full body" red light therapy treatments, and then see what is the "minimum effective size" of device can achieve those benefits.
According to many brands and salespeople, full-body red light therapy can deliver every possible benefit studied in the thousands of articles on PBM and LLLT.
However, we know that most of these medical claims are extrapolated from targeted treatments using small devices, lasers, clusters of LEDs/Lasers held in contact with the skin.
When in reality we can only find 11 studies using whole-body Red Light Therapy, so we only know of limited applications like for athletic recovery, fibromyalgia, and long-COVID.
These applications actually require whole-body treatment, it would be reckless to treat the whole body and a lot of healthy cells with a therapy when only a targeted region needed treatment. Since healthy cells will only run into the biphasic dose response sooner, and red light therapy is more effective when targeting malfunctioning cells.
Studies have shown more consistently successful results with targeted skin-contact therapies and that full-body treatments get less consistent results. 
UnderDosing and OverDosing on Full-Body Panels
Full body light therapy is often speculated to simultaneously underdose the target tissue by lacking penetration with non-contact treatment, and also paradoxically overdose on the Total Joules to the body.
One review article on the use of Red Light Therapy for Sports Performance found that the whole-body PBM studies performed worse than targeted treatments.
"Therefore, we consider that whole-body PBMT has as its main limitation the lack of contact with the target tissue, and the optical profile (or focus on different deep tissue) affects substantially the power density in the muscles and the modulation of the mitochondrial activity, and so the effects of the whole clinical trial are corrupted." 
One of the failed whole-body LED studies notes that their delivered dose was 473,400 Total Joules. They comment that successful studies have used 60-300 Joules for large muscle groups and 20-60 Joules for small muscle groups. 
The researchers cannot ignore the possibility that the whole-body treatment delivered over a thousand times more total energy than the typical dose - leading to cause a biphasic dose response that explains the lack of benefits. 
It is rather impressive that Full-Body light therapy can exist in this limbo of being both inherently underdosed and overdosed at the same time.
This is where we need to appreciate the systemic effects of getting a reasonable amount of Total Joules per treatment.
Systemic Blood Sugar Treatment:
One study on systemic blood sugar response exposed patients backs to 670nm LED light therapy.
The area was 800cm^2, intensity was 40mW/cm^2, and they quantified the dose as 28,800 Joules.
So again notice that many studies are using Total Joules rather than J/cm^2 for these large devices:
"participants exposed a 800 cm2 region of upper back to 670 nm light for 15 min at an intensity of 40mW cm− 2 (28,800 J)." 
The study specifically notes that they can achieve systemic results with a relatively localized treatment, and not needing 100% full body light therapy.
"Significant reduction in blood glucose was observed following local red light illumination of the body, rather than requiring whole body exposure." 
This shows us that we get a whole-body effect by just targeting the torso. This could be achieved similarly with a "half-body" or other smaller panel for a systemic effect on the whole body.
Systemic Anti-Viral Treatment:
One research group has used a 940nm LED Vest for several human studies on the systemic effects on the body. 
They have treated the systemic effects and inflammation from viral respiratory illnesses.
"The LED system parameters over the vest area were total optical power of 6 W and an average power density of 2.9 mW/cm2, corresponding to 5.4 kJ total optical energy during the 900 s of irradiation time. "
So even with a relatively low intensity of 2.9mW/cm^2, because they are treating a large area the Total Joules is 5,400 (5.4 kJ = 5,400 J).
And of course they were successful in achieving a systemic "whole body" effect for an important virus that causes systemic inflammation - again by treating a large area of the torso with Low Intensity but Thousands of Total Joules.
Study: Full-Body vs Smaller Device
One study compared the results of a LED Whole Body device to an LED Helmet for treating Long-Covid symptoms for 14 patients. 
They used the same intensity of 24mW/cm^2 for 14 minutes leading to a dose of 20.2 J/cm^2. 
However, the full-body device covered 18,000 cm^2 and the helmet only covers 650 cm^2. Leading to a total dose of 363,000 Total Joules for whole-body and 13,130 Total Joules for the helmet. 
This is a perfect example where the "dose" of 20 J/cm^2 appears to be the same for both devices. This is why J/cm^2 is so deceptive. The differentiating factor is the coverage area and Total Joules when comparing the doses of different devices.
Despite the big difference in coverage area and Total Joules, both modalities delivered the same benefits based on statistical significance. 
Since Long-Covid symptoms like brain fog are often a product of lingering systemic inflammation, it makes sense that both devices could offer a reduction in symptoms through systemic mechanisms.
This shows that even a relatively small device helmet device delivers comparable results to a whole-body device.
Half Body Panels are the Best Full Body Light Therapy Device Size
How big of a device do you need for full body red light therapy? What is the best size of red light therapy device in inches or centimeters?
A half-body sized panel covering one side of the torso or head has been shown to deliver full-body systemic results in these 4 human studies. This can be delivered with anywhere from 2.9 mW/cm^2 to 40mW/cm^2 of intensity, since even at relatively low intensities covering a large area delivers a large amount of Total Joules.
Studies have confirmed that half-body LED devices deliver systemic full-body benefits for several applications. A relatively small helmet delivered similar benefits to a full-body pod. The worlds leading researcher often discusses proper dosing of full-body light therapy in terms of Total Joules, and doesn't mention needing 100% skin coverage.
A systemic benefit can be gotten from as little as a few thousand (1,000's) Joules up to tens of thousands (10,000's) of Joules. So simply multiplying your typical J/cm^2 dose by the area of your device (cm^2), you can get a rough idea for your Total Joules dose.
Full Body Devices Vs Effective Dosing
Despite the overbearing salespeople insisting you need 100% coverage for any benefits at all, larger devices have not shown to significantly improve results than a reasonably sized half-body panel. The dosing and effects of Whole Body Red Light Therapy have been inconsistent so far with full body devices in the research.
Large whole-body light therapy devices can deliver hundreds of thousands of Joules even at relatively low intensity (24-28 mW/cm^2), which have been shown to be effective in cases requiring full-body treatments like intense athletic recovery, fibromayalgia, and long-Covid.
However, the larger devices must be used with caution to not overdose on the extremely high Total Joules, often taking advice from Dr.Hamblin that the intensity should be lowered to around 10-20mW/cm^2 to avoid overdosing on Total Joules.
Certainly, a large Whole Body Red Light Therapy device is luxurious and relaxing to engulf the entire body in light. However, it may not be necessary for the benefits of red light therapy.
If we believe the sensational marketing of needing huge devices and excessive intensities, then perhaps those brands and salespeople are more focused on placebo effects and profits than evidence-based effective doses.
Red Light Therapy can help a lot more people if we appreciate the usage of simple devices delivering reasonable intensities at manageable sizes. This can make it not only more affordable and accessible, but in many cases will prevent overdosing on Total Joules anyway.
Since non-contact whole-body devices lack the penetration and deliver unprecedented Total Joules compared to typical clinical grade devices - we will need more studies in the future to understand how to properly dose them.