Example: Lumen
Convert 1600 lm to klm.
Result: —
Photometry • Radiometry • Acoustics • Imaging
Light, Optics & Sound Unit Converter
Convert Photometry and Illumination units (Lumen, Lux, Candela, Luminance), Radiometry units, Acoustics units (including Decibel), and Imaging units (Frequency, Wavelength, Resolution). Results update instantly and the formula panel shows the conversion steps.
Lux: lx = lm/m²
Bel: 1 B = 10 dB
Wave: v = f·λ
nm, µm, THz
ppi ↔ px/cm
Core idea
Each category converts through a base unit (lm, lx, cd, cd/m², W, W/m², W/sr/m², Hz, m, ppi).
Photometry vs radiometry
Photometry uses human vision weighted units (lm, lx). Radiometry uses physical power units (W).
Decibel note
dB is a logarithmic ratio. This page converts dB ↔ bel, and keeps linear power (W, mW) in a separate category.
Interactive Converter
Pick a category, choose units, enter a value, then copy the result. Use Swap to reverse units.
Category explanation
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Select a category to see what it means and where it is used.
Base unit: —
Plain language
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Common formula
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Real world uses
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Tip: You can type commas (like 12,500). The converter reads it as 12500.
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Enter a value to convert
Conversion Formula
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Notes: This tool converts units. Some topics (like dB to watts) require a reference value and are not purely "unit conversions."
Unit Comparison Table
Quick reference showing all available units, their symbols, and conversion factors.
| Category | Base Unit | Unit Symbol | Conversion Factor |
|---|---|---|---|
| Photometry: Luminous Flux | lm | lm | 1.0 |
| Photometry: Luminous Flux | lm | klm | 1,000 |
| Photometry: Luminous Flux | lm | Mlm | 1,000,000 |
| Illumination: Illuminance | lx | lx | 1.0 |
| Illumination: Illuminance | lx | klx | 1,000 |
| Illumination: Illuminance | lx | fc | 10.76 |
| Luminosity: Luminous Intensity | cd | cd | 1.0 |
| Luminosity: Luminous Intensity | cd | mcd | 0.001 |
| Luminosity: Luminous Intensity | cd | kcd | 1,000 |
| Luminance (Display Brightness) | cd/m² | cd/m² | 1.0 |
| Luminance (Display Brightness) | cd/m² | nit | 1.0 |
| Luminance (Display Brightness) | cd/m² | stilb | 10,000 |
| Radiometry: Radiant Power | W | W | 1.0 |
| Radiometry: Radiant Power | W | mW | 0.001 |
| Radiometry: Radiant Power | W | µW | 0.000001 |
| Radiometry: Radiant Power | W | kW | 1,000 |
| Radiometry: Irradiance | W/m² | W/m² | 1.0 |
| Radiometry: Irradiance | W/m² | mW/cm² | 10 |
| Radiometry: Irradiance | W/m² | µW/cm² | 0.01 |
| Radiometry: Radiance | W/(sr·m²) | W/(sr·m²) | 1.0 |
| Radiometry: Radiance | W/(sr·m²) | mW/(sr·cm²) | 10 |
| Acoustics: Decibel Scale | dB | dB | 1.0 |
| Acoustics: Decibel Scale | dB | B | 10 |
| Waveforms: Frequency | Hz | Hz | 1.0 |
| Waveforms: Frequency | Hz | kHz | 1,000 |
| Waveforms: Frequency | Hz | MHz | 1,000,000 |
| Waveforms: Frequency | Hz | GHz | 1,000,000,000 |
| Waveforms: Frequency | Hz | THz | 1,000,000,000,000 |
| Waveforms: Frequency | Hz | rpm | 0.0167 |
| Spectral/Optics: Wavelength | m | m | 1.0 |
| Spectral/Optics: Wavelength | m | cm | 0.01 |
| Spectral/Optics: Wavelength | m | mm | 0.001 |
| Spectral/Optics: Wavelength | m | µm | 0.000001 |
| Spectral/Optics: Wavelength | m | nm | 0.000000001 |
| Spectral/Optics: Wavelength | m | in | 0.0254 |
| Imaging/Display: Resolution Density | ppi | ppi | 1.0 |
| Imaging/Display: Resolution Density | ppi | dpi | 1.0 |
| Imaging/Display: Resolution Density | ppi | px/cm | 2.54 |
| Imaging/Display: Resolution Density | ppi | px/mm | 25.4 |
Worked Examples
These examples are pre computed so visitors can sanity check results and learn common magnitudes.
Examples are computed on page load
Example: Lux
Convert 500 lx to klx.
Result: —
Example: Wavelength
Convert 550 nm to µm.
Result: —
Example: Candela
Convert 1200 mcd to cd.
Result: —
Example: Decibel
Convert 30 dB to bel.
Result: —
Example: Resolution
Convert 300 ppi to px/cm.
Result: —
Example: Luminance
Convert 1000 cd/m² to stilb.
Result: —
Example: Irradiance
Convert 100 W/m² to mW/cm².
Result: —
Example: Frequency
Convert 1500 MHz to GHz.
Result: —
Quick Visual Chart: Visible Spectrum
This chart shows typical visible wavelengths (violet to red) in nanometers on a simple log scale bar view.
No libraries used, pure canvas
Tip: The chart is intentionally simple to keep your page fast.
Illuminance Levels Reference
Common illuminance values for reference in various environments and conditions.
| Environment | Illuminance (lux) | Description |
|---|---|---|
| Starlight (clear night) | 0.0001–0.002 | Very dim, barely visible |
| Twilight | 0.01–1 | Dusk or dawn |
| Hallway (typical) | 50–100 | Standard indoor corridor |
| Office (standard) | 320–500 | Recommended workspace lighting |
| Retail store | 500–1000 | Bright, merchandise display |
| Operating room | 1000–10000 | Surgical precision lighting |
| Outdoor (shade) | 10000–25000 | Shaded daylight |
| Direct sunlight | 32000–100000 | Full sun, very bright |
Frequency & Wavelength Spectrum
Common frequency and wavelength ranges across the electromagnetic spectrum.
| Spectrum Type | Frequency | Wavelength | Notes |
|---|---|---|---|
| Radio (VLF) | 3–30 kHz | 10–100 km | Very long wavelength |
| Radio (AM) | 535–1605 kHz | 186–560 m | Amplitude modulated broadcasting |
| Radio (FM) | 88–108 MHz | 2.78–3.41 m | Frequency modulated broadcasting |
| Microwave (WiFi) | 2.4–5 GHz | 60–125 mm | Wireless networking |
| Infrared (Far) | 0.3–3 THz | 100–1000 µm | Heat radiation |
| Infrared (Near) | 3–430 THz | 700–2500 nm | Just beyond visible red |
| Visible Red | 430–480 THz | 625–700 nm | Long visible wavelength |
| Visible Green | 520–610 THz | 490–575 nm | Peak human eye sensitivity |
| Visible Violet | 610–790 THz | 380–490 nm | Short visible wavelength |
| Ultraviolet (UV-A) | 790–950 THz | 315–400 nm | Long UV, causes tanning |
| Ultraviolet (UV-B) | 950–1200 THz | 280–315 nm | Medium UV, causes burns |
| X-rays | 30–30000 PHz | 0.01–10 nm | Medical imaging |
Display Resolution Reference
Common device resolutions and their pixel densities.
| Device Type | Resolution | PPI | Quality |
|---|---|---|---|
| Standard Monitor | 1920×1080 (24") | 92 | Good for desktop |
| High-DPI Monitor | 3840×2160 (27") | 163 | Sharp, professional |
| Laptop (standard) | 1920×1080 (15.6") | 141 | Clear |
| Laptop (Retina) | 2560×1600 (13") | 227 | Very sharp |
| Smartphone (standard) | 1080×1920 (5.5") | 401 | Crisp |
| Smartphone (high-res) | 1440×3120 (6.1") | 522 | Extremely sharp |
| Printer (laser) | — | 600–1200 | High quality text |
| Printer (photo) | — | 2400–4800 | Photographic quality |
FAQ
What is the difference between lumen, lux, candela and luminance?
Lumen (lm) is total light output (luminous flux). Lux (lx) is light on a surface (illuminance), defined as lx = lm/m². Candela (cd) is intensity in a direction. Luminance (cd/m²) describes surface brightness (like a screen).
Can I convert decibel (dB) to watts directly?
Not as a pure unit conversion. dB is logarithmic and needs a reference (like dBm, dBW, a voltage reference, and often impedance). This page converts dB ↔ bel and separately converts linear power units (W, mW).
How are wavelength and frequency related?
They are linked by wave speed: v = f × λ. For light in vacuum, c ≈ 299,792,458 m/s, so f = c/λ.
What is the difference between photometry and radiometry?
Photometry measures light weighted by human eye sensitivity (lumen, lux, candela, luminance). Radiometry measures physical electromagnetic radiation power without weighting (watts, W/m², W/(sr·m²)).
What is PPI and why does it matter?
PPI (pixels per inch) measures display resolution density. Higher PPI means sharper text and images. Most human eyes can distinguish pixels below ~300 PPI at normal viewing distances. Smartphones typically have 300–500+ PPI.
What is a nit and how is it used?
A nit is another name for cd/m² (candela per square meter), a unit of luminance. It measures display brightness. Typical monitors are 100–300 nits, HDR displays can exceed 1000 nits.