Light, Radiation

Light, radiation and sound share an awkward property: the quantities that describe them are easy to confuse with one another. Lumens measure the total light a source emits, lux measures how much of it lands on a surface, and candela describes intensity in a direction. A very bright bulb can still leave a desk badly lit if it is mounted in the wrong place, which is a lux problem rather than a lumen problem.

Radiation units are similarly layered. The becquerel counts decay events, the gray measures energy absorbed by tissue, and the sievert weights that absorbed dose by the biological harm the radiation type causes. Older sources use curies, rads and rems, so anyone reading historical measurements needs a reliable bridge to modern units.

Sound is measured on a logarithmic decibel scale, which is why a ten decibel increase represents roughly a doubling of perceived loudness rather than a ten percent change. This converter brings these families together so lighting designers, radiographers, safety officers and audio engineers can move between the units their sources use.

How to use the Light, Radiation

1. Pick the quantity family you are working with: light, radiation or sound.
2. Select the source unit exactly as it appears in your document or instrument.
3. Choose the target unit required by your standard or report.
4. Enter the measured value and read the conversion.
5. Record the unit alongside the number in your documentation, since these units are easily mistaken.

Examples

• A lighting designer checks whether a fitting rated in lumens will deliver the 500 lux required over an office desk.
• A radiography student converts an older dose figure quoted in rems into millisieverts.
• An acoustic consultant compares sound pressure readings taken on instruments using different weightings.

Frequently asked questions

What is the difference between lumens and lux?

Lumens describe total light output from a source. Lux is lumens per square metre falling on a surface, so it depends on distance and beam spread as well as the bulb.

How do sieverts relate to grays?

A gray measures absorbed energy per kilogram. A sievert applies a weighting factor for the biological effect of the radiation type, so the two are equal for X-rays and gamma rays but not for alpha particles.

Why can decibels not be added normally?

The scale is logarithmic. Two equally loud sources together produce about three decibels more than one, not double the figure.

Are these conversions suitable for regulatory reporting?

Use them for working estimates and cross-checks. Formal reporting should follow the calibrated instruments and procedures your standard specifies.

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