BU-1S MED Test — Simple Step-by-Step Guide
For first-time users of the BU-1S UV phototherapy device
These instructions are written for the patient / user. This guide is a supplement to your physician's prescription; all treatment must be performed under medical supervision. Items marked Recommended are practical tips added to fill gaps in the original equipment manual; they are not part of the manual text.
What is an MED test, in plain words
MED = Minimal Erythema Dose. It is the lowest UV dose that makes your skin show a faint, clearly-bordered pink patch 24 hours after exposure. Everyone's skin is different, so you must measure your own before the first real session. Without it, the dose is a guess — too high burns you, too low does nothing and builds resistance.
Prepare
You need: the BU-1S device, the MED tester plate (the small plate with 5 holes), the lamp comb, UV-blocking goggles, and your physician's note of your skin type (I–VI).
Know your skin type
Pick the type that matches you (Fitzpatrick scale):
| Type | Sun reaction | Skin color |
|---|---|---|
| I | Burns easily, never tans | Very fair, blue eyes, red hair |
| II | Burns easily, tans a little | Fair, blue/green/gray eyes |
| III | Sometimes burns, tans easily | White to light brown |
| IV | Rarely burns, tans easily | Light brown |
| V | — | Brown |
| VI | — | Black |
Find your base dose
The 100% hole uses the base dose below. The other 4 holes are fixed ratios of it.
| Skin type | Base dose (J/cm²) Hole 1 (100%) | Hole 2 (80%) | Hole 3 (60%) | Hole 4 (40%) | Hole 5 (20%) |
|---|---|---|---|---|---|
| I | 0.40 J/cm² | 0.32 J/cm² | 0.24 J/cm² | 0.16 J/cm² | 0.08 J/cm² |
| II | 0.65 J/cm² | 0.52 J/cm² | 0.39 J/cm² | 0.26 J/cm² | 0.13 J/cm² |
| III | 0.90 J/cm² | 0.72 J/cm² | 0.54 J/cm² | 0.36 J/cm² | 0.18 J/cm² |
| IV | 1.20 J/cm² | 0.96 J/cm² | 0.72 J/cm² | 0.48 J/cm² | 0.24 J/cm² |
| V | 1.50 J/cm² | 1.20 J/cm² | 0.90 J/cm² | 0.60 J/cm² | 0.30 J/cm² |
| VI | 1.60 J/cm² | 1.28 J/cm² | 0.96 J/cm² | 0.64 J/cm² | 0.32 J/cm² |
All values in J/cm².
Calculate exposure time
Each hole's dose must be turned into seconds. Formula:
Time (seconds) = Dose (J/cm²) × 1000 ÷ Intensity (mW/cm²)
The intensity is on the device's factory card (Table A-1). For UVB it is 3.2–7.2 mW/cm². Use your actual measured intensity — the lamp weakens with age.
Example (reference intensity 7.0 mW/cm²): Type III → Time = 900 ÷ 7.0 = 129 seconds (one exposure). If your device's actual intensity differs, recompute with the formula above.
Do the test — one exposure, the plate does the rest
The MED tester plate has 5 windows that each transmit a different fraction of the UV (100% / 80% / 60% / 40% / 20%), numbered 1 to 5 starting from the rounded end. You do one exposure for the time T you calculated in Step 3. The plate automatically delivers the 5 different doses to the 5 spots — no covering or separate timing of individual holes.
Example (reference intensity 7.0 mW/cm²): Type III → T = 900÷7.0 = 129 s of one exposure. The 5 spots receive:
| Hole | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Transmittance | 100% | 80% | 60% | 40% | 20% |
| Dose (J/cm²) | 0.90 | 0.72 | 0.54 | 0.36 | 0.18 |
Place the plate on unexposed, healthy skin (inner forearm, buttock, or waist) — not on lesions, not on the face. Keep the 3 cm distance with the lamp comb. Wear goggles. Hold the plate flat and steady for the whole exposure. The plate is not symmetrical: the rounded end is the Hole 1 side. Keep that orientation every time — otherwise you will read the 5 spots backwards after 24 hours.
Read the result after 24 hours
Look at the 5 spots. Starting from the lowest dose (Hole 5) and moving up, find the first spot with a faint, clearly-bordered pink patch. That dose is your MED.
| Hole 1 | Hole 2 | Hole 3 | Hole 4 | Hole 5 |
|---|---|---|---|---|
| 100% | 80% | 60% | 40% | 20% |
| 0.90 | 0.72 | 0.54 | 0.36 | 0.18 |
| red | red | red | faint | none |
read direction
MED = the dose of the first faint spot = 0.36 J/cm² (this example)
The manual says "the fourth hole firstly shows the light erythema." Do NOT read this as "Hole 1 first." It means: scanning from the lowest dose upward, Hole 4 is the first to show a faint reaction. Reading it wrong can make your MED 2.5× too high and cause a burn.
Your MED → starting dose → exposure time
The manual only gives a safe fallback of "10 seconds for first-timers." Clinically, the usual starting treatment dose is 70% of your MED (50% if cautious).
Example: MED = 0.36 → starting dose ≈ 0.25 J/cm².
Convert the dose to seconds — the BU-1S works by time, not by dose
The BU-1S has no dose/time mode: it cannot turn your J/cm² dose into exposure seconds for you, so you must do the math yourself with the same formula from Step 3.
Time (seconds) = Starting dose (J/cm²) × 1000 ÷ Intensity (mW/cm²)
Example: 0.25 J/cm² × 1000 ÷ 7.0 = 36 seconds. Set the device's timer (or time it with a stopwatch) for that many seconds, start the treatment, and turn off the power when the time is reached. Use the same measured intensity you used in Step 3.
Then increase gradually (about 10–20% per session) and watch the skin reaction. If clear redness or pain appears, stop and step back.
Record it
Write your skin type, MED, starting dose, and each session's time in the patient log (Appendix C) so you and your doctor can track progress.
Safety reminders
Wear UV-blocking goggles during the test and every treatment — you and anyone in the room.
Cover untreated skin (face, neck, ears) with cloth or SPF 15+ sunscreen.
No bystanders in the room during exposure.
Do not treat over skin eruptions unless your physician directs it.
Any pain or skin changes: stop and contact your doctor.
Units trap: the MED table uses J/cm²; the time tables in Appendix B use mJ/cm² (1 J = 1000 mJ). Don't mix them up.
Based on the BU-1S equipment manual (V1.0, 202101), MED section. The MED tester plate uses fixed hole-size attenuation: one exposure delivers 100/80/60/40/20% doses to the 5 spots automatically. Items marked Recommended fill gaps left by the manual and are kept separate from the manual text. This document is for operational guidance only and contains no manufacturer branding.