Borosilicate (B270) Optical Glass

Cost-effective optical glass for visible-light applications

Transmission
350–2000 nm (optimized for 400–700 nm)
Refractive Index
~1.523 @ 587.6 nm
Hardness
5-6 Mohs
Density
2.58 g/cm³
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Quick Answer

Borosilicate B270 is a cost-effective optical glass optimized for visible light applications (400–700 nm). It offers good transmission and homogeneity at lower cost than BK7. Commonly used for displays, simple lenses, filters, and applications where extreme optical precision is not required.

What Is Borosilicate (B270)?

Borosilicate B270 is a crown glass offering good optical quality in the visible spectrum at an economical price point. It is widely used in applications where BK7-grade performance is not essential but better optical quality than float glass is needed.

B270 is particularly popular for display cover glass, simple lens elements, filter substrates, and general-purpose optical components in consumer and industrial applications.

Optical & Physical Properties

Reference data — verify with PhotonEdge for project-specific specifications.

Transmission Range350–2000 nm (optimized for 400–700 nm)
Refractive Index~1.523 @ 587.6 nm
Density2.58 g/cm³
Hardness5-6 Mohs
CTE8.3 × 10⁻⁶ /K
Thermal Conductivity~1.1 W/(m·K)
dn/dT3 × 10⁻⁶ /K
Softening/Melting Point~820°C (softening)

Typical Applications

Display Optics

Cover glass and substrates for LCD, OLED, and projection displays

Simple Lens Elements

Cost-effective singlet lenses for non-critical imaging

Filter Substrates

Substrates for absorption and interference filters

General Optics

Educational, alignment, and non-precision optical systems

Coating Considerations

AR Visible

Broadband AR for 400-700nm. R < 0.5% per surface.

Typical use: Imaging and display applications

Mirror Coatings

Substrate for visible-range mirror coatings.

Typical use: General-purpose mirrors

Uncoated

Raw glass surface acceptable for many display and filter applications.

Typical use: Display cover glass, filter substrates

Engineering Considerations

Optical Quality

Lower homogeneity than BK7. Not recommended for precision imaging or laser applications.

UV Performance

Transmission drops below 350nm. Not suitable for UV applications.

Cost Advantage

Significantly lower cost than BK7 for visible-only applications where premium optical quality is not needed.

Thermal Limits

Lower thermal resistance than BK7. Not suitable for high-power laser or extreme temperature applications.

Material Comparison

vs BK7

B270 is lower-cost but lower optical quality. BK7 for precision; B270 for cost-sensitive visible applications

vs Float Glass

B270 has better optical homogeneity and transmission than standard float glass

vs Fused Silica

B270 is economy VIS-only; Fused Silica is premium UV-VIS-NIR

Frequently Asked Questions

What is B270 glass?

B270 is a borosilicate crown glass optimized for visible light applications. It offers good optical quality at lower cost than BK7.

When should I choose B270 over BK7?

Choose B270 when your application is visible-light only, cost-sensitive, and doesn't require the highest optical homogeneity.

Can B270 be used for UV applications?

Not recommended. B270 transmission drops significantly below 350nm. Use UV Fused Silica for UV applications.

What is the refractive index of B270?

Approximately 1.523 at 587.6 nm (sodium d-line).

Is B270 suitable for laser optics?

For low-power visible laser alignment or display purposes, yes. For precision or high-power laser systems, BK7 or Fused Silica is recommended.

Need Borosilicate (B270) Optics?

Describe your application and wavelength requirements. Our engineering team will recommend the optimal material grade and specifications.

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Optical Material

BK7 Optical Glass

BK7 is the most widely used optical glass for visible and near-infrared applications. A borosilicate crown glass, BK7 offers excellent optical clarity, good homogeneity, and reasonable cost — making it the default choice for many general-purpose optical components.

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Key Optical Properties

Property Value
Transmission Range 350 nm – 2.0 μm
Refractive Index 1.5168 @ 587.6nm
Thermal Expansion 7.1 × 10⁻⁶ /K (20-300°C)
Density 2.51 g/cm³
Knoop Hardness 610 HK

Advantages

  • Excellent visible transmission (>92% per surface uncoated)
  • High material homogeneity and consistency
  • Good chemical resistance and stability
  • Cost-effective — widely available in stock sizes
  • Suitable for most visible and NIR applications

Limitations

  • Not suitable for UV below 350nm
  • Higher thermal expansion than fused silica
  • Lower LIDT than fused silica for high-power lasers
  • Hygroscopic under extreme humidity conditions
  • Limited IR transmission beyond 2μm

Typical Applications

Imaging lenses and objectives

Beam splitters and prisms

General-purpose windows

Spectrometer optics

Machine vision systems

Common Coating Options

Standard coating types available for this material. Custom coating designs available on request.

Broadband AR (VIS, VIS-NIR)
Anti-reflection single-layer MgF₂
Protected/enhanced aluminum
Dielectric HR and partial reflector
Beam splitter coatings

Products Using Borosilicate Glass

Custom optical components available in borosilicate glass for cost-sensitive applications. Standard catalog products typically use BK7 or UV Fused Silica.

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