TRUE-365^TM 24V 365nm UV LED strip for alternative process exposure

TRUE-365 is a high-output, 5-meter, 24-volt reel of true 365nm UV-A LEDs, built for exposing photopolymer gravure plates, platinum/palladium, cyanotype, gum, carbon transfer and other UV-sensitive processes. With 240 LED chips per meter, it gives you a dense, even light source for building an exposure unit at any size.

TRUE-365^TM comes from Prints on Paper Studio, the Vermont photogravure studio that also supplies Torelief WS95HK2 polymer photogravure plates. Its output is verified at 3,000 to 7,300 µW/cm², depending on the voltage and amperage you supply.

Why 365nm LEDs instead of fluorescent or metal halide

• The right wavelength. Photopolymer plates and most iron-based and dichromate processes respond strongly to the UV-A band around 365nm. Narrow-band LEDs put their energy where the emulsion or polymer reacts, instead of spreading it into visible light and heat.
• Consistent exposures. LEDs reach full output almost instantly and don’t fade the way aging fluorescent tubes do, so your results stay repeatable from plate to plate.
• Cool, compact and efficient. No ballasts, no warm-up and far less heat than metal halide, in a 9mm strip that fits a flat, low-profile unit.
• Long life. Rated for 50,000 hours, so there are no bulbs to replace every season.

240 LEDs per meter for dense, even light

TRUE-365^TM packs 240 LED chips into every meter of strip, so the light sources sit close together along the strip. Lay the 9mm strips about 1mm apart in their densest configuration, and you get an almost continuous field of UV across the exposure bed. Dense light means more even exposure across the plate and fewer hot spots.

At that spacing, one 5m reel covers about 0.05 m² (roughly 77 square inches) of LED grid. For larger grids, add more reels and wire them in parallel. See “Sizing your LED grid” below for how much grid your plates need.

Why 24V

Most UV strips run on 12V. TRUE-365^TM runs on 24V. At the same wattage, a 24V strip draws half the current, which means:

• Less voltage drop along the run, for more even brightness from one end of the strip to the other.
• Longer runs and larger exposure beds on the same wiring.
• Lighter wiring and less heat in your connections.

To eliminate voltage drop completely, TRUE-365^TM strips can be wired positive and negative at both ends. Feeding power from both ends keeps the brightness uniform across the whole length of every strip. Even illumination across the bed is what gives you even exposure across the plate, so this matters as much as raw output.

Adjustable output: 3,000–7,300 µW/cm²

TRUE-365^TM output scales with the power you give it. At the low end, around 3,000 µW/cm², you get gentle, controllable exposures for small plates and testing. At full drive, up to 7,300 µW/cm², you get short exposure times for production work. Pair the reel with an adjustable or dimmable 24V supply to dial in intensity for your process and keep exposure times in a practical range.

TRUE-365 specifications

Consistent output from 2.5″ to 7.5″

The best working distance for TRUE-365 is between 2.5 and 7.5 inches from the plate. In our testing, irradiance (µW/cm²) doesn’t change anywhere in that range. You can set the array height to suit your enclosure, vacuum frame or contact frame without your exposure times changing.

Sizing your LED grid: the 2.5″ overhang rule

For even exposure all the way to the edges, the LED grid needs to extend 2.5 inches beyond every edge of whatever you’re exposing. Without that overhang, the light falls off near the edges and the borders of your plate or print come out underexposed.

To size your grid, add 5 inches to each dimension of your plate. Here’s what that means for common plate sizes, up to 31″ × 42″:

Strip lengths assume the densest layout, with strips about 1mm apart (10mm center to center). Reel counts are rounded up to whole reels. Power supply figures are 16W (about 0.67A) per meter plus 25% headroom for the strip actually used. Amps = watts ÷ 24V. Your supply, or your supplies combined, should be rated for at least this current at 24V. For larger units, splitting the load across several supplies is common. Wider spacing uses less strip.

Use a UV dosimeter for repeatable exposures

We strongly recommend controlling your exposures with a UV dosimeter, such as the Ian Leake exposure calculator, instead of a plain timer. As LEDs warm up during an exposure, their output dips slightly. A dosimeter measures the actual UV energy reaching the plate and ends the exposure when the target dose is reached. That gives you exactly the same exposure every time, whether the unit is cold or has been running all afternoon.

Choosing a power supply

Use a regulated 24V DC supply with about 25% headroom over the total wattage of the strip you’re running. A supply working well below its limit runs cooler and holds its voltage steady, and steady voltage means consistent exposures.

• 1 reel (5m, 80W / 3.3A): 100W / 4.2A minimum at 24V (a 150W / 6.25A supply is a common size)
• 2 reels (10m, 160W / 6.7A): 200W / 8.3A minimum at 24V (a 240W / 10A supply is a common size)
• Larger units: multiply 16W (or about 0.67A) by the total meters of strip, then by 1.25. To convert watts to amps at 24V, divide by 24.

Building your exposure unit

• Lay strips in a tight, even grid. For maximum density, space the 9mm strips about 1mm apart, and extend the grid 2.5″ past every edge of your largest plate.
• Mount the array 2.5–7.5″ from the plate. Output is consistent anywhere in that range.
• Wire strips in parallel, not in series. Feed each run from a terminal or distribution block so every strip sees the same voltage. Daisy-chaining strips end to end makes the first strips brighter than the last.
• Power both ends. Connect positive and negative at both ends of each strip to eliminate voltage drop across long runs.
• Mount on aluminum. An aluminum backing sheet pulls heat away from the LEDs, which keeps output stable and extends their life. For long exposures, add a fan.
• Let a new unit settle, then calibrate. Run the array for a few minutes before making step-wedge tests so your readings reflect normal operating temperature.
• Calibrate for your process with a dosimeter. Expose a step wedge or test strip to find your standard dose, then let a UV dosimeter, such as the Ian Leake exposure calculator, end each exposure so heat-related output dips never change your results.

UV safety

365nm UV is mostly invisible but can damage eyes and skin. Run your unit inside a closed, light-tight enclosure. If you’ll be looking at or working near the lit array, wear UV-blocking safety glasses rated to ANSI Z87.1. Never look directly into the LEDs.

Note: under 365nm light, small components on the strip may glow a faint yellow or white. This is normal fluorescence and doesn’t affect output.

Frequently asked questions

Can I use TRUE-365 to expose photopolymer gravure plates?

Yes. 365nm is well matched to steel-backed photopolymer plates like Torelief WS95HK2, for both direct-to-plate and film-positive workflows.

Does it work for platinum/palladium, cyanotype and other alt processes?

Yes. Platinum/palladium, cyanotype, Van Dyke, salt, gum bichromate, carbon transfer and photo emulsions for screen printing are all sensitive in the UV-A range that 365nm LEDs deliver.

How many reels do I need?

First size your grid: add 5″ to each dimension of your largest plate, for a 2.5″ overhang on every side. At the densest layout (about 10mm center to center), divide the grid width by 10mm to get the number of strip rows, multiply by the grid length, and divide by 5m. For example, an 8″ × 10″ plate needs a 13″ × 15″ grid, which takes about 12.5m of strip, or 3 reels.

How far should the LEDs be from the plate?

Between 2.5 and 7.5 inches. Irradiance stays the same throughout that range, so pick whatever height fits your frame.

Why do I need a dosimeter if the output is verified?

LED output dips slightly as the strips warm up. A timer gives the same seconds, but not necessarily the same dose. A UV dosimeter, such as the Ian Leake exposure calculator, measures the actual UV delivered and gives you exactly the same exposure every time.

Can I run TRUE-365 on a 12V power supply?

No. TRUE-365^TM is a 24V strip and needs a regulated 24V DC supply. A 12V supply won’t drive it properly.

Can I replace the strips in my VerifiedUV™ or other 12V unit with TRUE-365?

Yes, but you’ll also need to switch to a 24V power supply, since the two systems run at different voltages. Re-calibrate your exposure times after switching.

How do I control the output?

Output depends on the voltage and current you supply. Use an adjustable or dimmable 24V supply to set intensity anywhere from about 3,000 to 7,300 µW/cm², and use a dosimeter to keep the total dose of each exposure consistent. The 16w/meter spec for these lights puts out approximately 7000 µW/cm² so if you are really wanting to up the voltage/wattage you need to make sure you spec a proper power supply with enough coverage. And also make sure you have the right heatsink and airflow in the unit!

Can I cut the strip?

Yes, but only at the marked copper cut points. Wire each section back to your supply in parallel.

Build Your Own Exposure Unit with TRUE-365 LEDs!

Here is the Build of Materials spreadsheet that we made for our own exposure unit at Prints on Paper Studio: https://docs.google.com/spreadsheets/d/1zvK_SmrW-yL8QTqpIV40MP5EJedxYv7wr396RYUFUO0/edit?usp=sharing

And below is the wiring diagram for both the power supply unit and the wall-mounted vertical exposure grid enclosure. The whole thing can exposure plates at 31×42 inches in minutes and it only uses 8″ of horizontal space in a room because it’s all mounted on the wall. It does require both 120v and 240v wall outlets though!