Seconds, mJ/cm², and UV meters: what the words mean
Time and delivered light energy are related, but they are not interchangeable across devices. This page explains the language and never supplies treatment targets.
Last updated
Seeing different units can make a plan feel like a math test. You do not need to calculate or convert your treatment on your own.
The useful goal is to understand which unit your written plan uses, where the number comes from, and who to call when the device, lamp, skin, or instructions change.
Time is not the same as delivered energy
Seconds tell you how long the light is on. They do not make one device equal to another.
Delivered energy depends on the measured output and setup of the exact equipment. That is why a time from another person, another device, or an older plan is not a safe shortcut.
Evidence and limits
Confidence: reasonably supported · Checked:
- Guidelines for narrowband ultraviolet B phototherapy (opens in a new tab) - British Association of Dermatologists and British Photodermatology Group
Published . Supports NB-UVB uses, accurate light measurement, quality checks, home-treatment governance, and condition-specific care.
Limit: It does not choose a device or care setting for one person and SteadySkin does not reproduce treatment schedules from it.
Ask your care team Keep device, coverage, and treatment decisions with the people who know your health and the exact equipment.
What mJ/cm² means
The unit describes delivered light energy over an area of skin.
Some equipment and protocols use energy-per-area language. Accurate measurement and regular quality checks help make delivered light consistent. This page does not convert a unit into a treatment setting.
Evidence and limits
Confidence: reasonably supported · Checked:
- Guidelines for narrowband ultraviolet B phototherapy (opens in a new tab) - British Association of Dermatologists and British Photodermatology Group
Published . Supports NB-UVB uses, accurate light measurement, quality checks, home-treatment governance, and condition-specific care.
Limit: It does not choose a device or care setting for one person and SteadySkin does not reproduce treatment schedules from it.
Ask your care team Keep device, coverage, and treatment decisions with the people who know your health and the exact equipment.
What a UV meter can and cannot do
A UV meter or dosimeter measures output. It does not decide what your skin should receive. Whether a home user needs a meter depends on the exact device, support plan, and care team.
Do not buy a meter or change a setting because an online guide says you should. Ask who checks output, how often the device needs service, and what to do if a reading or lamp behavior changes.
Evidence and limits
Confidence: reasonably supported · Checked:
- Guidelines for narrowband ultraviolet B phototherapy (opens in a new tab) - British Association of Dermatologists and British Photodermatology Group
Published . Supports NB-UVB uses, accurate light measurement, quality checks, home-treatment governance, and condition-specific care.
Limit: It does not choose a device or care setting for one person and SteadySkin does not reproduce treatment schedules from it.
- Frequently Asked Questions About Home Use Devices (opens in a new tab) - US Food and Drug Administration
Supports checking operating needs, patient capabilities, support contacts, instructions, and whether a particular home device requires a prescription.
Limit: It does not say every home medical device has the same prescription or coverage rules. Those depend on the exact device, state, supplier, and plan.
Ask your care team Keep device, coverage, and treatment decisions with the people who know your health and the exact equipment.
What should I ask at my next appointment?
Use these words as written, or change them to fit what you need.
- Which unit does my written plan use, and where does that number come from?Saving keeps this on your device and needs JavaScript, which is off in this browser.
- Who checks the output of my exact device?Saving keeps this on your device and needs JavaScript, which is off in this browser.
- What should I do if the device, lamp, skin reaction, or instructions change?Saving keeps this on your device and needs JavaScript, which is off in this browser.