Quick answer: To make LED lights black, turn them off: black means no visible light. To create a blacklight effect, choose a UV-A light source, which Wikipedia describes as emitting ultraviolet with very little visible light (blacklight).
This guide separates darkness, a purple-looking lamp and a source intended to make fluorescent materials glow. It replaces the old remote-button and coloured-tape recipes with a selection checklist and a strip-power example. Start with the effect you want before choosing equipment.
Choose between darkness and a blacklight effect
If you want darkness, use the off control. If you want objects to glow, look for a blacklight source: according to Wikipedia's blacklight article, invisible ultraviolet can cause certain materials to emit visible light. Those are different goals, even though both get called “black LED lights.”
| What you mean by “black” | What to choose | What to judge |
|---|---|---|
| No light coming from the strip | Turn the strip off | Whether it stops producing visible light |
| A black-looking strip or housing | Choose the physical finish you want | The appearance of the unlit hardware |
| A blacklight effect on fluorescent materials | Choose a UV-A source | The material's visible response; according to Wikipedia, some materials emit visible light under UV |
| A purple-looking lamp | Decide whether purple appearance alone meets your goal | In a filtered blacklight lamp, the violet glow is visible light that escapes the filter, not the UV itself, according to Wikipedia |
A black housing is a finish choice; it is not a specification for emitted light. Likewise, a remote preset called “blacklight” does not tell you the source's wavelength. For general lighting calculations alongside this project, the LEDask home hub collects the site's planning tools.
Why a purple glow does not prove UV output
Judge a blacklight by its specified output, not by how purple it looks. According to Wikipedia, the violet glow seen from a filtered blacklight is visible light that escapes the filter; it is not the ultraviolet radiation itself.
That distinction explains why recreating a lamp's visible appearance is the wrong target. The effect you are trying to obtain is illumination of a fluorescent material, not simply a coloured view of the lamp. According to the same blacklight source, the material produces visible light in response to invisible UV.
Do not use a sequence of red and blue button presses as a UV specification. No reliable source shows that a remote-control colour sequence produces UV-A, or that coloured marker layers over an ordinary strip make a suitable UV source, so neither trick is a dependable way to get a blacklight effect.
If you already have a strip, identify whether its stated function is visible colour lighting or UV lighting. If UV output is unspecified, that leaves the blacklight requirement unanswered. Select a source expressly intended for that requirement instead of treating a purple appearance as confirmation.
Read wavelength and filter descriptions separately
UV-A describes a wavelength band; a filter description concerns the light a lamp lets through. According to Wikipedia's ultraviolet article, UV-A spans 315–400 nm, and the lower limit of the visible spectrum is conventionally 400 nm. A nanometre, abbreviated nm, is a unit of length used here to describe wavelength.
According to Wikipedia's blacklight article, lamps labelled BLB, meaning blacklight blue, have a dark filter and glow dimly violet. Lamps labelled BL lack that filter, produce more visible light and look blue. The article also gives 365 nm as a commonly cited BLB peak.
Use these descriptions for different decisions. A wavelength identifies where the output lies; the BL or BLB distinction describes a lamp's filtering and visible appearance. Do not turn a commonly cited peak into a universal requirement for every LED strip, or assume a label alone predicts the result on your chosen material.
For a practical selection sequence:
- Decide whether the goal is darkness, a physical black finish or fluorescence.
- For fluorescence, choose a source whose description explicitly identifies UV-A output.
- Read its wavelength and any filtering description separately.
- Select the strip length and calculate its electrical demand from its own power rating.
- Evaluate the intended material's response, rather than judging the project solely by the lamp's visible colour.
Estimate the power for a UV strip
Calculate electrical demand from watts per metre and length. The LED strip calculator uses power = watts per metre × length and current = power ÷ voltage. Its strip presets are not UV product specifications, so the example below uses explicitly assumed ratings instead of assigning a visible-light preset to a UV strip.
Assumed inputs: strip length 5 m, rated demand 12 W/m, and operating voltage 24 V. These describe a hypothetical strip, not a measured product or a typical UV rating.
- Total power = watts per metre × length = 12 W/m × 5 m = 60 W.
- Current = power ÷ voltage = 60 W ÷ 24 V = 2.5 A.
- The calculator's planning figure adds 20% headroom: multiplier = 1 + 20 ÷ 100 = 1.2; planning power = 60 W × 1.2 = 72 W.
- It then rounds upward to a 10 W increment: supply power = ceil(72 ÷ 10) × 10 = ceil(7.2) × 10 = 8 × 10 = 80 W.
Here, “ceil” means round upward to the next whole number. The resulting power figure is a planning allowance, not a UV performance or exposure calculation. It does not establish how strongly an object will fluoresce. Use the actual strip's voltage and power requirements when selecting a compatible supply; use a qualified electrician for any mains-voltage wiring.
Match the strip to its location
An outdoor effect needs a strip suitable for its environment. According to Wikipedia's LED strip article, uncoated tape has no water resistance; coated strips may carry IP65 or IP67 ratings, or IP68 with suitable sealed connections.
That makes the strip covering and its connections part of the purchase decision. Do not treat a coating on the tape as a description of the entire assembled installation. For an outdoor project, establish the assembled product's location suitability before choosing it for its colour or effect. These ratings do not answer the separate question of whether the source produces UV-A.
FAQ
Can I make my LED strip black using its remote?
For darkness, use off. For a blacklight effect, do not rely on a colour recipe: according to Wikipedia, a blacklight emits UV-A with very little visible light, so a remote colour name is not enough to establish the required output.
Does purple light mean my strip is producing UV?
No: purple appearance alone does not establish UV output. According to Wikipedia, a filtered blacklight's violet glow is visible light escaping the filter, not the UV itself.
What wavelength counts as UV-A?
According to Wikipedia, UV-A is 315–400 nm, with 400 nm conventionally marking the visible spectrum's lower boundary. Use a product's stated wavelength rather than its photographed colour.
Why do objects glow under a blacklight?
According to Wikipedia, some materials fluoresce under ultraviolet illumination, emitting visible light. That visible response is the effect you see on the object.
Should I use the calculator's ordinary strip preset for a UV strip?
Only treat a preset as applicable if its assumed electrical demand matches the strip you are planning. The worked example uses the power formula directly with assumed inputs; it does not claim that a calculator preset represents a particular UV product.
Can I put uncoated LED tape outdoors?
Do not select uncoated tape for a location requiring water resistance. According to Wikipedia, uncoated LED tape has no water resistance; choose an assembly suited to the intended location.
Jack Shi
Founder & editor, LEDaskJack Shi builds and writes LEDask, an independent LED-lighting tools project operated by clooms. He designs the calculators, checks their formulas and reference values against published engineering data, and writes the guides across the site.
