Lamps for Vitamin D Phototherapy

Comparison of UV Lamp Types: UVB-Narrowband, UVB-Broadband & UVA-Tanning

What is the best fluorescent UV lamp type for Vitamin D production?

There are three main candidate fluorescent ultraviolet lamp types for Vitamin D production in human skin, they are:

  • UVA Cosmetic Tanning Lamps, as found in tanning salons worldwide. These lamps contain a small percentage of UVB.

  • UVB-Broadband Lamps. In use for at least 50 years for the medical treatment of psoriasis, but now being used less often in favor of UVB-Narrowband lamps.

  • UVB-Narrowband Lamps. A relatively new development, used very successful for the medical treatment of psoriasis.

All of these lamps will produce Vitamin D, but the optimal lamp type has not been medically established. This study compares the technical aspects of these lamps and their action spectrums, but is not intended to definitively answer the question of which is the optimal lamp type. That can only be established through peer reviewed medical study. Solarc Systems makes no medical claims in this regard.

Different wavelengths of “light” produce different effects on materials. Many important processes have been scientifically studied to determine the relative contribution of each wavelength to the studied process. Graphs known as “action spectrum” are used to describe these relationships. The greater the “action spectrum sensitivity”, the more responsive is the process to that wavelength.

The Vitamin D Action Spectrum has been thoroughly studied [Ref: CIE (International Commission on Illumination)] and shows that the most therapeutic wavelengths are in the UVB range as shown in Figure 1. In the following sequence of pictures, additional action spectrums and UV lamp spectral curves will be added to explain the benefits and risks for each lamp type. Note that the relative size of the lamp curves are dependent on the power and number of lamps in the device, but that the relative distribution of wavelength does not change.

The action spectrum for “sunburning” of human skin, also known as “erythema”, has also been studied. (CIE) Erythema is undesirable because it causes patient discomfort, is a risk factor for skin cancer, and reaching that state does not produce any additional Vitamin D. The Erythema Action Spectrum (in red) shows similarities to the Vitamin D Action Spectrum, but an interesting opportunity appears in the region of 298 to 316 nm, where the Vitamin D sensitivity exceeds the erythema sensitivity, as shown in grey in Figure 2. In this region, the ratio of Vitamin D produced to erythema received is at its most favorable; a “sweet spot” with a peak at about 308 nm. Interestingly, this region corresponds very nicely with the Psoriasis Action Spectrum shown in green (296 to 313 nm).

Common UVA cosmetic “tanning” lamps have been shown to produce Vitamin D. This is possible because, even though most of the lamp’s energy is in the UVA region, there is still a small amount of UVB produced, limited by regulatory bodies such as the US-FDA to not exceed about 8%, and typically 3.5% to 5%, and even less in Europe. The small shaded area in Figure 3 (where the curves intersect) gives a pictorial representation of the Vitamin D producing potential of these UVA tanning lamps (in this example, “350BL” type, where 350 = wavelength peak and BL = Black Light). These lamps provide the vast majority of their energy in the UVA range, which does not provide any Vitamin D, increases treatment time, causes skin tanning (which inhibits Vitamin D production) and subjects the patient to some UVA erythema (the erythema action spectrum extends all the way to 400 nm – each wavelength contributes). The UVA spectral curve does however most closely approximate the sun’s natural spectrum.

A logical option for making Vitamin D is to use “UVB-Broadband” lamps. These lamps do a good job of spanning the Vitamin D Action Spectrum as pictorially represented by the grey shaded area in Figure 4. The vast majority of energy produced is in the UVB range, which produces Vitamin D, but the light is spread broadly across UVB wavelengths (280 to 315 nm), including very significant amounts deep into the most potent regions of the Erythema Action Spectrum. This means that the user must take great care when dosing, so as to not exceed the Minimum Erythema Dose (MED) and cause skin burning. UVB Broadband lamps typically provide little tanning effect because dosing is limited by erythema, long before the UVA content can cause tanning. In other words, the spectral profile is too heavily weighted in UVB to allow significant tanning effects. Although some people do report getting tanned, the more common outcome is slight pinkness, or little or no effect when dosing conservatively. UVB-Broadband lamps have been used to treat psoriasis for more than 60 years, but the possibility of burning has always been a concern. In the USA, UVB-Broadband lamps require a physician prescription per 21CFR801.109. Solarc’s UVB Broadband models have only a “UVB” suffix, such as 1740UVB.

A more recent option for making Vitamin D is to use “UVB-Narrowband” lamps, such as the Philips TL100W/01-FS72 6-foot long 100 watt T12 lamp, made popular for its superior effectiveness in the treatment of psoriasis, vitiligo and other skin disorders. This lamp has a very large amount of energy concentrated at 310-311 nm, and a minor peak at about 306 nm. The grey shaded area in Figure 5 shows only partially its Vitamin D making potential, because the peak of the UVB-NB curve is so high, its contribution cannot fully be represented pictorially. These lamps produce Vitamin D, and they take advantage of the “sweet spot” between the action spectrum curves of Vitamin D and Erythema as explained at Figure 2 (the theoretical ratio of erythemogenic potential of UVB-Broadband to UVB-Narrowband is in the range of 4:1 to 5:1). This means that more Vitamin D can be produced before skin burning occurs, accurate dosing is less important, and the treatment is theoretically safer and easier to use, especially in the home environment. In psoriasis patients, UVB Narrowband is capable of producing good therapeutic results without the patient ever reaching the erythemogenic threshold. (Haykal & DesGroseilliers 2006, Walters 1999) For these reasons, UVB-Narrowband is now the phototherapy treatment of choice for many skin diseases, and is considered to be less aggressive than UVB-Broadband phototherapy. To wit, Solarc Systems Home UVB-Narrowband sales exceed UVB-Broadband sales about 100:1. If UVB-NB is the best waveband for psoriasis, is it also the best waveband for Vitamin D? Several medical studies have shown the effectiveness of UVB-NB in producing Vitamin D, but more research is needed to determine which waveband is best. Solarc has sold several UVB-Narrowband devices specifically for Vitamin D. As with UVB-Broadband, UVB-Narrowband lamps typically provide little tanning effect because dosing is limited by erythema, long before the UVA content can cause tanning. In other words, the UVB-NB spectral profile is too heavily weighted in UVB to allow significant tanning effects. In the USA, UVB-Narrowband lamps require a physician prescription per 21CFR801.109. Solarc’s UVB-Narrowband models have an “UVB-NB” suffix in the model number, such as 1780UVB‑NB.

Another way to evaluate lamp types is to study the action spectrum ratio of Vitamin D to Erythema, with the expectation that the best fitting lamp type will be the best for treatment purposes. In other words, what wavelength produces the most Vitamin D with the least erythema? For this we invented a new curve called the “Normalized Vitamin D to Erythema Ratio”, or “NVDER” for short, shown in Yellow in Figure 6. This NVDER curve is created by dividing the Vitamin D Action Spectrum by the Erythema Action Spectrum, and “normalizing” the result, so the maximum value is 1.0, just like an action spectrum. This new curve is really just another way to show the “sweet spot” as discussed at Figure 2. It shows that the best ratio (peak) occurs at 308 nm. All three lamp types intersect the NVDER curve, but the UVB Narrowband curve is likely the best fit, with its peak at 310 to 311 nm. Also note that, because the peak of the UVB-NB curve is so high, the UVB-Narrowband curve shows only partially its Vitamin D making potential, and that its contribution is not fully represented in this picture format. Note that the peak of the UVB-Narrowband curve is about ten times higher than the UVB-Broadband curve, thus the source of the name “Narrow Band”.

Solarc’s UVB-Narrowband models have an “UVB-NB” suffix in the model number, such as 1780UVB‑NB. Solarc’s UVB Broadband models have only a “UVB” suffix, such as 1740UVB. Solarc does not manufacture UVA tanning devices specifically, but all device families will accept UVA bulbs (350BL PUVA).

Health Canada has recently granted Solarc Systems Inc. permission to add “Vitamin D Deficiency” to the “indications for use” of our UVB and UVB-NB devices. Indications for use are health candidates for which we can legally advertise. 


The figures used in this document are simplified representations. The UVB-Broadband curve is derived from the Solarc/SolRx 1740UVB and the UVB-Narrowband curve is derived from the Solarc/SolRx 1760UVB‑NB.

Please appreciate that the information provided here is just a collection of commonly available material, and not a substitute for the advice of your physician. We encourage you to research this important topic further. As with natural sunlight, long term use of a UVB phototherapy device can cause premature aging of the skin and skin cancer.

For more information, see these other related Solarc webpages: Vitamin D Phototherapy FAQ,  Understanding Narrowband UVBSolarc Systems Canadian Home Page.

References & Links:

Action Spectrum for the Production of PreVitamin-D3 in Human Skin CIE 174:2006

Erythema reference action spectrum and standard erythema dose

ISO-17166:1999(E) | CIE S 007/E-1998 Canada’s Food Guide  An official publication of Health Canada.

The Canadian Cancer Society Search: “Vitamin-D”.

2006 North American Conference on UV, Vitamin-D and Health. Key messages endorsed by the Canadian Cancer Society, Canadian Dermatology Association, Osteoporosis Canada, and many other organizations. (pdf)

Vitamin D Council A nonprofit group of concerned citizens that believe many humans are needlessly suffering and dying from Vitamin-D Deficiency.

Sunarc Sunlight, Nutrition And Health Research Center An organization devoted to research, and education relating to the prevention of chronic disease through changes in diet and lifestyle.

Book: The UV Advantage by Michael R. Holick, PH.D., MD and Mark Jenkins 1st Edition 2003, ISBN 0-7434-8647-1

Wikipedia entry for Vitamin D

PARRISH JA, JAENICKE KF (1981) Action Spectrum for phototherapy of psoriasis. J Invest Dermatol. 76 35

WALTERS I, (1999) Suberythematogenic narrow-band UVB is markedly more effective than conventional UVB in treatment of psoriasis vulgaris. J Am Acad Dermatol 1999;40:893-900 HAYKAL K-A, DESGROSEILLIERS J-P (2006)

Are Narrow-band Ultraviolet B Home Units a Viable Option for Continuous or Maintenance Therapy of Photoresponsive Skin Diseases? Journal of Cutaneous Medicine & Surgery, Volume 10, Issue 5 : 234-240

This website is not intended for use by residents of the USA. Vitamin-D Deficiency is not an US-FDA approved Indication for Use. For more information, see our Regulatory webpage.