Irradiance Comparison Test

SolRx 120UVB-NB versus a Competitive Device


The purpose of this informal test is to compare the irradiance (light power) of two commercially available handheld Narrowband-UVB phototherapy devices at their “recommended treatment distance”. The two devices are the twin-bulb SolRx 120UVB-NB and the single bulb competitor’s device. This test was conducted by Solarc Systems Inc. and has not been supervised or audited by any third party. To the best of our ability as professional engineers, we have performed this test with complete fairness to our worthy competitor. We encourage others to replicate our findings.


1. Three (3) new Philips PL-S9W/01/2P Narrowband UVB bulbs were selected from the same original shipping box and colour coded red-blue-green. The date code on each bulb was “A6” (January 2006).
2. All three bulbs were burned-in for 20 minutes and allowed to cool.
3. Three side-by-side tests were performed; Test 1, Test 2, and Test 3. After each test, the wands were opened-up and the bulbs were rotated between the devices, so over the course of the three tests, the three bulbs were sampled equally. This practically eliminates the possibility of a more powerful bulb skewing the results. The bulbs were allowed to cool to room temperature before each test.
4. When testing, both devices are started simultaneously and light meter readings taken at various times, as indicated by the stopwatch in the photo. Readings for each device were taken as close together in time as possible. Light meter readings were taken at the “recommended treatment distance” specified by devices’ User’s Manual. For the SolRx 120UVB-NB, this is at the clear acrylic window. For the competitor’s unit, this is at 1.25 inches from the face of the wand. A small strut made from a paper clip was applied to the light meter sensor to set the offset distance for the competitor’s device. The sensor was positioned by hand, centered laterally, and at the same longitudinal position relative to the end of the bulbs (50mm).
5. Photos were taken of the actual light meter readings received, as shown below. The photos show the device irradiance on the light meter display in mW/cm^2, and the “run time” on the stopwatch in minutes:seconds. That is, the amount of time that the bulbs have been running from cold-start. All photos are straight from the camera and completely unretouched. The photos on the left are of the competitor’s device. The photos on the right are of the SolRx 120UVB-NB.
6. The light meter was an International Light Model IL1400A calibrated for UVB-Narrowband in December 2005 on Certificate #512015216. The SolRx 120UVB-NB serial number was 1B223.


The irradiance for the three tests of the SolRx 120UVB-NB was: 11.87, 12.60, 9.75 mW/cm^2.

The irradiance for the three tests of the competitor’s unit was: 4.18, 4.56, 3.90 mW/cm^2.

For the three tests, the 120UVB-NB therefore has 2.84, 2.76, and 2.50 times more irradiance than the competitor’s device; or on average, 2.7 times more UVB-Narrowband light power.


The SolRx 120UVB-NB has considerably better irradiance than the competitor’s device, nominally by a factor of two to three times. This large difference in irradiance is not due to the device having two bulbs instead of one; rather, it is the distance from the bulbs that is the major contributor, and made possible by the 120UVB-NB’s clear, acrylic window barrier. The role of two bulbs is primarily to improve the treatment area shape and size (trying to make it more square-like, instead of long and skinny). Reflector design is also important. It is interesting to note that the clear, acrylic window on the 120UVB-NB blocks about 10% of the light, but its role as a barrier to allow the skin to get closer is crucial to the design. The competitor’s device also likely suffers light blockage from the plastic bar down its center (between the two tubes of the bulb).

Test Photos:

All test photos are untouched. There have not been any modifications to these photos after they are taken by the digital camera; for example, by programs such as Adobe Photoshop© or similar programs.

p1010116 100-Series Irradiance

Test 1A: Competitor’s device with red coded bulb. Runtime = 4:59 (minutes:seconds). Light meter display reads 4.18 mW/cm^2.

p1010117 100-Series Irradiance

Test 1B: 120UVB-NB with green/blue coded bulbs. Runtime = 5:11 (minutes:seconds). Light meter display reads 11.87 mW/cm^2 (2.84 times the irradiance of test 1A).

p1010122 100-Series Irradiance

Test 2A: Competitor’s device with green coded bulb. Runtime = 2:30 (minutes:seconds). Light meter display reads 4.56 mW/cm^2.

p1010123 100-Series Irradiance

Test 2B: 120UVB-NB with red / blue coded bulbs. Runtime = 2:42 (minutes:seconds). Light meter display reads 12.60 mW/cm^2 (2.76 times the irradiance of test 2A).

p1010124 100-Series Irradiance

Test 3A: Competitor’s device with blue coded bulb. Runtime = 12:09 (minutes:seconds). Light meter display reads 3.90 mW/cm^2.

p1010125 100-Series Irradiance

Test 3B: 120UVB-NB with red / green coded bulbs. Runtime = 12:21 (minutes:seconds). Light meter display reads 9.75 mW/cm^2 (2.50 times the irradiance of test 3A).