As temperature increases, TLCs transition through a visible spectrum of colors. Starting from black (below the active range), the color shifts to Red, then Green, then Blue, and finally back to Black again as the temperature exceeds the active range. This change is fully reversible — the color sequence repeats each time the temperature moves through the active range.

Both are thermochromic technologies, but they differ in key ways:

• Liquid Crystals transition through a full spectrum of visible colors (Black → Red → Green → Blue → Black). They are highly temperature-precise, require specialized manufacturing, and are commonly used in precision gauges, thermometers, and NDT applications.

• Leuco Dyes transition between one color and clear (colorless). They are easier to incorporate into standard manufacturing processes, less temperature-precise, and more common in packaging, toys, and labels.

LCR Hallcrest liquid crystal products cover a broad temperature range:

• DigiTemp Thermochromic Sheets: 68°F–135°F (20°C–57°C)
• Digi-Temp® Thermometers: -22°F to 248°F (-30°C to 120°C)
• FeverScan™ Forehead Thermometers: 94°F–106°F (34°C–41°C)

Custom temperature ranges are available depending on the application.

. 

LCR Hallcrest offers liquid crystal products in several formats:

• Ready-to-use polyester sheets (DigiTemp Thermochromic Sheets — 12″×12″)
• Self-adhesive strip thermometers (Digi-Temp® series)
• Forehead temperature indicators (FeverScan™)
• Custom coatings and inks for specialized applications

Many products are available with or without pressure-sensitive adhesive backing.

DigiTemp Thermochromic Sheets are ready-to-use polyester sheets coated with microencapsulated Thermochromic Liquid Crystal (TLC). They are finished and cut to 12″×12″ and are available with or without an adhesive back. The sheets display the full Black→Red→Green→Blue→Black color change as temperature increases through the active range.

DigiTemp Thermochromic Sheets specifications:

• Size: 12″ × 12″
• Substrate: 5 mil clear polyester
• Coating: Silkscreen application of microencapsulated TLC coating + black backing ink
• Backing: Optional pressure-sensitive adhesive with release liner
• Temperature Range: 68°F–135°F (20°C–57°C)

The following standard ranges are available (Red Start ±1°C / Blue Start ±2°C):

• R20C5B: Red starts at 20°C (68°F), Blue starts at 25°C (77°F)
• R25C5B: Red starts at 25°C (77°F), Blue starts at 30°C (86°F)
• R29C4B: Red starts at 29°C (84°F), Blue starts at 33°C (91°F)
• R30C5B: Red starts at 30°C (86°F), Blue starts at 35°C (95°F)
• R35C1B: Red starts at 35°C (95°F), Blue starts at 36°C (97°F) — narrow bandwidth
• R35C5B: Red starts at 35°C (95°F), Blue starts at 40°C (104°F)
• R40C5B: Red starts at 40°C (104°F), Blue starts at 45°C (113°F)
• R45C5B: Red starts at 45°C (113°F), Blue starts at 50°C (122°F)

Digi-Temp® Thermometers are a comprehensive system of self-adhesive strip thermometers based on proprietary liquid crystal formulations. They provide instant, continuous temperature readout with no batteries or glass, are non-toxic, and cover a wide temperature range from -22°F to 248°F (-30°C to 120°C). The current temperature is displayed as a green color event on the strip.

As temperature increases through the active range:

1. Black (below active range)
2. Red (first color visible as temperature rises)
3. Green (mid-range temperature)
4. Blue (upper end of active range)
5. Black again (above active range)

The process reverses as the temperature drops — the material is fully reversible and repeatable.

Bandwidth refers to the temperature span (in °C or °F) over which the full color change sequence (Red through Blue) occurs. A narrow bandwidth (e.g., 1°C) means the full color change happens very quickly with a small temperature change, making it ideal for precise temperature indication. A wider bandwidth (e.g., 5°C) means the transition is more gradual and visible over a broader range.

Common applications include:

• Promotional products and ad specialties
• Instructional and educational use
• General non-destructive testing (NDT) and thermal mapping
• Research (engineering, aerospace)
• Medical/clinical temperature monitoring (forehead thermometers)
• Industrial process monitoring and quality control
• Room and environmental temperature monitoring
• Aquarium and refrigeration temperature monitoring

FeverScan™ is a forehead temperature indicator product that uses TLC technology to provide a fast, simple clinical temperature monitoring system. The thermometer is applied to the center of the forehead and displays temperature as a series of discrete color events — each showing green when the indicated temperature is reached. It is disposable or reusable, latex-free, and available in standard and extended temperature ranges for use in hospitals and at home.

Digi-Temp® thermometers offer the following accuracy levels:

• -30°C to 59°C: ±1°C
• 60°C to 89°C: ±2°C
• 90°C to 120°C: ±3°C

For DigiTemp Thermochromic Sheets, Red Start and Green Start temperatures are accurate to ±1°C (±2.0°F). Blue Start, Blue-to-Black, and bandwidth temperatures are accurate to ±2°C (±4.0°F).

Yes. Thermochromic Liquid Crystal products are fully reversible. The color change sequence repeats every time the material passes through its active temperature range — whether heating or cooling. There is no degradation from normal repeated use.

Yes. LCR Hallcrest can formulate liquid crystal products for custom temperature ranges across a broad spectrum. Contact your supplier to discuss specific temperature targets, bandwidth requirements, and substrate or format needs.