UVB lighting produces ultraviolet B radiation, a specific band of light with wavelengths between 280 and 315 nanometers. It sits between the shorter, more dangerous UVC rays and the longer UVA rays that make up most of the ultraviolet light reaching Earth’s surface. UVB is the portion of the spectrum responsible for sunburns, vitamin D production, and a range of medical and agricultural applications that rely on artificial lamps to replicate what the sun does naturally.
Where UVB Fits in the Light Spectrum
Visible light, the kind your eyes can detect, spans roughly 400 to 700 nanometers. Just below that visible range lies ultraviolet radiation, divided into three categories: UVA (315 to 400 nm), UVB (280 to 315 nm), and UVC (100 to 280 nm). The shorter the wavelength, the more energy the light carries. UVB sits in the middle, energetic enough to cause real biological effects but not so short-wavelength that the atmosphere blocks it entirely.
The ozone layer absorbs most solar UVB before it reaches the ground, but a meaningful fraction still gets through. That partial filtering is why UVB exposure varies so much by altitude, latitude, time of day, and season. At high noon in summer near the equator, UVB intensity is many times higher than on a winter morning in northern latitudes. Artificial UVB lamps bypass the atmosphere altogether, delivering controlled doses for specific purposes.
How UVB Affects the Body
UVB’s most well-known biological role is triggering vitamin D production. When UVB photons in the 295 to 315 nm range strike your skin, they convert a cholesterol compound called 7-dehydrocholesterol into previtamin D3. Your body heat then transforms that into vitamin D3, which enters the bloodstream and undergoes two chemical conversions in the liver and kidneys to become the active hormone your body uses for calcium absorption, immune function, and bone health.
The same energy that produces vitamin D also damages DNA. UVB is directly absorbed by the DNA in skin cells, causing adjacent building blocks in the genetic code to fuse together into abnormal structures. Your cells have repair mechanisms for this kind of damage, but repeated or intense exposure can overwhelm those defenses. Over time, accumulated DNA damage from UVB is a primary driver of skin cancer risk.
Eyes are also vulnerable. Short, intense UVB exposure can cause photokeratitis, essentially a sunburn on the surface of the eye. Symptoms include pain, redness, tearing, blurry vision, light sensitivity, and a gritty feeling. These typically resolve within 48 hours, but chronic low-level exposure over years raises the risk of cataracts and macular degeneration.
Medical Uses of UVB
Dermatologists use narrowband UVB phototherapy, centered around 311 to 312 nm, to treat skin conditions like psoriasis and vitiligo. The treatment involves standing in a light booth or using a handheld device for brief, carefully timed sessions. For vitiligo, a typical starting dose is 200 millijoules per square centimeter. For psoriasis, the starting dose is calibrated to each patient’s skin sensitivity, usually 50 to 70 percent of the minimum dose that would cause redness.
Sessions are repeated two to three times per week, with the dose gradually increasing as the skin adapts. The goal is to slow the overactive immune response driving these conditions without causing burns. Narrowband UVB has largely replaced older treatments that combined UVA light with a photosensitizing drug, because it’s effective with fewer side effects.
UVB in Reptile and Animal Care
Many reptiles, amphibians, and other captive animals need UVB light to synthesize vitamin D3, just as humans do. Without it, they can’t properly absorb calcium from food, leading to metabolic bone disease, a painful and potentially fatal condition. Desert species like bearded dragons need higher UVB intensity than forest-dwelling species that naturally live under heavy canopy cover.
Reptile UVB bulbs come in various strengths, often labeled by the percentage of their output that falls in the UVB range. A bulb marketed as “10% UVB” is designed for desert species, while a “5% UVB” bulb suits tropical animals. Placement matters significantly. UVB intensity drops off sharply with distance, so the lamp needs to be positioned at the right height above the basking spot, and screen or glass lids can filter out a large portion of UVB before it reaches the animal.
UVB for Plants and Agriculture
Plants have a dedicated photoreceptor for UVB called UVR8. When this receptor detects UVB radiation, it activates protective responses, most notably ramping up the production of flavonoids and other secondary metabolites. These compounds act as a natural sunscreen for the plant and also serve as defenses against insects and pathogens. For growers, this means UVB exposure can increase the concentration of flavor and aroma compounds in herbs, fruits, and vegetables.
Cannabis cultivation has generated particular interest in UVB supplementation. An early 1987 study found that supplemental UVB increased THC concentrations by up to 28 percent in drug-type cannabis plants. However, more recent and rigorous research has consistently failed to replicate that result. Multiple studies testing various UVB doses and durations on different cannabis cultivars found no significant enhancement of cannabinoid content, yield, or plant growth. At the highest UVB levels, researchers actually observed slight decreases in yield and photosynthetic efficiency. The early findings that fueled industry enthusiasm appear to be an outlier rather than a reliable effect.
Types of UVB Lamps
Two main technologies produce artificial UVB: fluorescent tubes and LEDs. Each has distinct strengths.
- Fluorescent UVB lamps are the established standard. A 22-watt fluorescent tube designed for UVB output delivers a broad spectrum from 280 nm through the UVA range. These lamps are efficient at producing UVB specifically and remain the most cost-effective option for most applications.
- UVB LEDs are newer and improving, but current models have a notable limitation. In one comparison, a 100-watt LED bar containing both UVA and UVB diodes delivered only about 6 microwatts per square centimeter of UVB. The 22-watt fluorescent produced seven times more UVB while consuming roughly one-fifth the power. The reason: UVB diodes make up only a small fraction of the LEDs on a typical UV bar, with UVA diodes outnumbering them about 15 to 1.
For applications where UVB specifically is the priority (reptile care, phototherapy, plant experiments), fluorescent technology still dominates. LED fixtures deliver more UVA per watt but lag far behind in UVB output. As LED efficiency improves, this gap will likely narrow, but for now, fluorescent remains the practical choice for targeted UVB delivery.
UVB Intensity and Measurement
UVB intensity is measured in microwatts per square centimeter (µW/cm²) for instantaneous output, or millijoules per square centimeter (mJ/cm²) for cumulative dose over time. The medical field uses a unit called the Minimal Erythemal Dose (MED), which represents the smallest UVB dose that causes visible redness on a given person’s skin. One MED equals about 21 mJ/cm², though the actual threshold varies widely by skin type.
A related unit, the Standard Erythemal Dose (SED), is fixed at 10.5 mJ/cm² and provides a skin-type-neutral way to quantify exposure. These units matter most in clinical phototherapy and UV safety, where precise dosing determines whether UVB heals or harms. For reptile keepers or indoor growers, a handheld UVB meter reading in µW/cm² is the simplest way to verify that a lamp is delivering the intended intensity at the animal’s or plant’s actual position.
Protecting Yourself Around UVB Sources
Whether you’re using a UVB lamp for reptiles, plants, or any other purpose, the same precautions apply. Never look directly at an active UVB source. Ordinary glass and most plastics block UVB effectively, which is useful for shielding but also means these materials will reduce the output reaching your intended target. UV-blocking safety glasses protect your eyes without the need to avoid the room entirely.
Skin exposure from incidental contact with reptile or horticultural UVB lamps is generally minimal because of the low wattage and the distance involved, but prolonged close-range exposure to bare skin should be avoided. If you’re using a higher-powered medical-grade device, follow the dosing protocol precisely, as the margin between a therapeutic dose and a burn is narrow.