Red and infrared light therapy works when the dose is correct. Not too little, not too much. In practice, it is about delivering a certain number of joules per square centimeter (J/cm²) to the target tissue, and controlling it with distance to the skin and time. Here you get a practical, number-based guide that makes it easy to dose correctly in everyday life with clinically anchored rules of thumb.

At Heat Sense, we design our CE-approved devices based on the same principles, so you can hit therapeutic windows for pain, inflammation, wound healing, and recovery without having to guess.

J/cm², mW/cm² and “fluence” explained briefly

• J/cm²: The total energy the tissue receives per square centimeter.
• mW/cm² or W/cm²: Irradiance or power density, i.e. the “strength” on the skin per square centimeter.
• The connection: Dose (J/cm²) = Irradiance (W/cm²) × Time (seconds).

Example: 130 mW/cm² is 0.130 W/cm². If you treat for 60 seconds, 0.130 × 60 = 7.8 J/cm² is delivered.

Note two things. First, the intensity drops dramatically when you increase the distance from the skin. Secondly, tissue has a “biphasic response”: Low to moderate doses stimulate, while excessively high doses can give less effect.

Which dose window is typically most effective?

Research consistently shows effect in low to moderate doses. There is no linear gain from turning it up without limit, and the yield often falls when you go significantly above the optimal ranges. Typical intervals: pain in muscles and joints 2–10 J/cm² per treatment point; wound healing and tissue regeneration 4–8 J/cm²; anti-inflammation 3–10 J/cm²; general PBM protocols with red and infrared 1–20 J/cm², typically at the low end. For 904–980 nm, lower energy is often used to achieve the same biological response. Do not imitate the laboratory 1:1, but stay within the windows, as double the dose does not give double the effect.

Wavelength and depth: choose the right one for the task

Red light around 630–660 nm is primarily absorbed in the top few millimeters of the skin and is ideal for superficial targets such as skin quality, scars, and superficial tendons. Infrared light around 800–850 nm penetrates deeper (typically 5–10 mm) and is better suited for muscles, tendon attachments, and joints. Longer infrared wavelengths such as 904–980 nm can reach 1–2 cm, but are often delivered in shorter pulses and with lower energy per point.

Shorter, visible red light often requires a slightly higher fluence if the target is deeper, while 810–830 nm is a workhorse for deeper structures, where a moderate dose has shown good results. 904 nm pulse lasers typically work with few joules per point. At Heat Sense, we combine 660 nm and 850 nm in several units to cover both surface and depth.

Distance makes a big difference

The intensity drops sharply when the distance is increased, and for small sources the strength can be halved in a few millimeters. Therefore, keep the unit in contact with the skin or as close as possible, and expect lower both surface dose and penetration if you keep too far away. Our wraps and masks are designed for contact, so you don’t have to measure distance, and handheld lasers can be pressed lightly against the skin for stability and maximum energy penetration.

Time in practice: how to calculate how long to treat

Use the simple formula: J/cm² = W/cm² × seconds. Below you will find approximate times for two typical irradiance levels seen in everyday life: 130 mW/cm² (0.130 W/cm²) and 380 mW/cm² (0.380 W/cm²).

The times apply in contact with the skin. If you increase the distance, the time increases sharply. In addition, continuous light and pulsed light can give slightly different tissue responses, even at the same J/cm². Many clinical protocols work with exposures of tens of seconds to a few minutes per point.

Doses distributed over an area: point-by-point or slow scanning

When treating larger areas, you can either work point-by-point or scan slowly. Point-by-point means that you divide the area into fields of approximately one spot size, give each spot its target dose (e.g. 6–8 J/cm²) and move on, which ensures uniform coverage. Slow scanning means that you move the unit with approximately the time per spot required to deliver the target dose; it takes a little practice, but works well over longitudinal tendons or muscle belly. A wrap or pad covers many cm² at once; here it makes sense to think in “per-point” equivalence, use shorter intervals per area and move the pad on to keep the local J/cm² within the target window.

Recommended windows by purpose

Start low in the range and adjust according to response. Pain in muscles/joints: 2–10 J/cm² per point, with typically good balance at 4–8 J/cm². Wounds, scars, and skin regeneration: 4–8 J/cm², as higher doses can inhibit healing. Anti-inflammation: 3–10 J/cm², where low to moderate fluence is typically most effective. Nerves/vessels and deeper tissue: 4–9 J/cm² at 810–830 nm; 0.8–4 J per point at 904 nm is often sufficient.

Safety, upper limits, and temperature

Photobiomodulation is well documented as gentle, but there are still reasonable limits to respect.

• If you clearly exceed 10–20 J/cm² per point on sensitive tissue, the gain often falls, and a feeling of warmth can occur.
• High irradiance over a short time can be safe if you stay within the target dose and avoid heating.
• The eyes are light-sensitive: always use the included glasses when using laser and when treating near the face.

Our products have built-in timers (e.g. 3 minutes on pen, 15 minutes on several wraps), so you avoid leaving the light on for too long. The timers are comfort features, not a requirement to use the entire period in one place on the body.

How to hit the target dose with Heat Sense units

You can dose precisely by combining irradiance, time, and area division.

• RLT pen (up to approx. 380 mW/cm² in contact): You hit 6–8 J/cm² with approximately 16–21 seconds per point. If you have an area of 8 points, this corresponds to just over 3 minutes in total, which matches the auto-timer.
• Light therapy pad/wrap (typically around 130 mW/cm²): 6–8 J/cm² is reached in approximately 46–62 seconds. Use 1–2 minutes per area, move on, and let the skin rest in between. You do not need to run the full 15 minutes in the same place.
• Face mask: Close contact and moderate intensity. Use short programs and repeat more often rather than prolonged exposure in one session, when the goal is skin quality and wound healing.

Note that figures may vary slightly between models. See the specific mW/cm² specifications in the manual or on the product page, and use the table above as a quick calculation aid.

Frequency and treatment course

The body responds best to repeated, controlled stimuli, and many achieve good results with short sessions several times a week. Give the tissue rest between sessions, and if the skin feels warm or sensitive, lower the dose or increase the pause.

• Acute conditions: 1–2 times daily for the first 3–7 days, then tapering down.
• Chronic ailments: 3–5 times a week for 3–6 weeks, then maintenance 1–3 times a week.
• Sport and recovery: Short session after training and possibly the next day on sore spots.

Five practical tips for keeping the dosage sharp

• Close contact with the skin
• Short, precise exposures per point
• Divide larger areas into fields
• Stay in the low to moderate J/cm² window
• Move the unit and let the tissue rest

Examples of dosage in everyday scenarios

Lower back pain, deep tissue: Use 850 nm as the main wavelength. Aim for 6–9 J/cm² per point with 20–25 seconds exposure at approx. 380 mW/cm². Cover 10–12 points and repeat 4 times a week.

Shoulder tendon, sore insertion: 660 + 850 nm. Start at 4–6 J/cm². At 130 mW/cm², this corresponds to 30–46 seconds per field. Hold the wrap for 1–2 minutes per sub-area and move on.

Chronic knee pain: 810–830 nm through the patellar tendon. 6–8 J/cm² per point. 16–21 seconds at 380 mW/cm². 8–10 points around the patella and joint line, 3–4 times a week.

Scars and superficial skin: 630–660 nm. 4–6 J/cm² per field. 30–46 seconds at 130 mW/cm². Spare the skin and repeat frequently rather than long sessions.

Frequently asked questions about dosage

How do I avoid “overtreating”? Use the target doses per point, keep close contact, and move the unit on. Use a timer or count seconds calmly.

Can I combine red and infrared in the same session? Yes. It is often used, as red light targets the surface, while infrared reaches deeper. Still keep the local J/cm² within the range.

What if I don’t know my unit’s mW/cm²? See the manual or contact support. As a rule of thumb, moderate light in contact for 30–90 seconds per point gives a useful dose for many purposes.

What about animals and fur? Part the fur, place the tip in contact with the skin, and expect a little longer time for the same J/cm² if the light does not penetrate directly down.

Why Heat Sense works with contact, timers, and clear specifications

Danish production and warehouse provide fast delivery 1–2 days and Danish support. CE-approved units document safety and quality. Irradiance in the range used in clinical protocols makes it possible to hit 4–10 J/cm² in seconds to a few minutes per point at home. Contact-based design, auto-timer and the possibility of pulsation on selected models make the use simple.

It makes everyday life simple: Choose the target dose, calculate a quick time interval based on mW/cm², keep close contact, and move on.

Quick reference: choice of dose and setting

After this explanatory paragraph, you get a short summary in list form that makes it easy to decide on a protocol for the next session.

• Pain, muscle/joint: 6–8 J/cm²: 16–21 sec at 380 mW/cm²; 46–62 sec at 130 mW/cm².
• Wound/scar: 4–6 J/cm²: 11–16 sec at 380 mW/cm²; 31–46 sec at 130 mW/cm².
• Inflammation: 3–10 J/cm²: choose at the low end for recent irritation; move up to the middle for chronic condition.
• Deep treatment: Prioritize 810–850 nm; for 904 nm pulse laser, 1–4 J per point is often enough.

One last piece of advice: Rather start low, measure the effect over a few sessions and adjust. Qualified frames for J/cm², correct distance and control of time usually give significantly better results than turning up everything at once. Should you be in doubt about dosing with your unit, our customer service will be happy to help you translate mW/cm² into practical times in your daily routine.