The words on a lighting truck

Kelvin is the color of a light, and mired is the same number in the unit gels are sold in: a million divided by the kelvin. CTO warms a light, CTB cools it, and plus or minus green fixes the tint. Below are the words crews use on set, and the labels you see in the app.

Updated October 2026 · Gel values are LEE Filters' published mired shifts, the same table the app uses

The words on the meter

Pick a word and the meter shows you where it lives. The four badges play on a light that gives them.

On the card

How sure it is

Buttons

HIGH, MEDIUM, LOW

Read the entry

The bounce boards, held still. The reading settles and the badge says HIGH.

Demonstration frame. We drew in the light from each lamp so you can try the meter here. On set, the app reads it through your camera.

Cutvey Meter · Glossary · 26 terms

Light and color

Kelvin K: The color of a light, as a temperature. Low numbers are warm and high numbers are cool: a candle sits near 1900 K, a tungsten film lamp is made to 3200 K, HMIs and daylight LEDs to 5600 K, and an overcast sky reads around 6500 K. The app's scale runs from 1,800 to 12,000 K.; Candle 1900 K · Tungsten 3200 K · HMI 5600 K
Mired: A million divided by the kelvin. 3200 K is 312.5 mired and 5600 K is 178.6. Gels are sold in mired because a gel moves any light by the same number of mired wherever it starts, so the same half CTO works on a window and on an LED. The word is short for micro reciprocal degree.; 1,000,000 ÷ 3200 K = 312.5 mired
Tint: The green to magenta side of a light's color, at right angles to kelvin. Fluorescent tubes and many LEDs run green. The app shows tint as a signed number over a scale marked GREEN · 0 · MAGENTA.; GREEN · 0 · MAGENTA
Lux lx: How much light falls on a surface. The app shows it in lux or foot-candles and works it out from the camera's exposure; it is not an incident reading from a light cell.; 1 foot-candle ≈ 10.76 lux
Tungsten: Film lamps with a glowing filament, made to 3200 K. On set the word also means anything balanced to 3200 K, such as a tungsten-balanced LED.; 3200 K · 312.5 mired
Daylight: Light at about 5600 K, the balance film lamps and cameras call daylight. The real sun and sky move with the weather, the time and the place.; 5600 K · 178.6 mired
HMI: A daylight-balanced lamp that makes its light with an arc, not a filament, and runs from a ballast. HMIs are made to about 5600 K.; 5600 K
Practical: A lamp that is in the shot, like a table lamp, a candle or a neon sign. It often lights the scene as well as sitting in it.
Bounce: Light sent off a board, a wall or a card to make it softer. A bounce picks up the color of the surface it comes off.

Gels

CTO Color temperature orange: A gel that warms a light by adding mired. LEE's Full CTO (204) adds 159, which takes 5600 K daylight to about 2960 K, a little warmer than tungsten. Half (205) adds 109, quarter (206) 64 and eighth (223) 26.; Full +159 · 1/2 +109 · 1/4 +64 · 1/8 +26
CTB Color temperature blue: A gel that cools a light by taking mired away. LEE's Full CTB (201) takes 137, which brings a 3200 K lamp to about 5700 K. Half (202) takes 78, quarter (203) 35 and eighth (218) 18.; Full −137 · 1/2 −78 · 1/4 −35 · 1/8 −18
Plus green: A green gel for a lamp, used to match it to green-running fluorescent tubes or LEDs. The app names plus green only as a rough hint, labeled PLUSGREEN, in quarter, half and full.
Minus green: A magenta gel that takes green out of a light, for a fluorescent tube or an LED that runs green. In the app it is MINUSGREEN, and it is a rough hint too.

White balance

Gray card: A card of neutral gray that reflects every color equally, so the camera reads the light rather than the scene. In the app you tap the reading to switch to GRAY CARD, then fill the frame with the card.
AWB Auto white balance: The camera's own guess at the color of the light, made from the whole picture. The app starts on AWB, and the gray card reading is one tap away.

Exposure

ND Neutral density: A filter that cuts light without changing its color, so you can keep your stop and your shutter in bright light. The strip under the reading in the app keeps a live ND figure for your ISO, stop, shutter and frame rate.; ND 0.9 = 3 stops = ND8
OD Optical density: How ND strength is written on cine filters: every 0.3 is one stop, so ND 0.3 is one stop, 0.6 two and 0.9 three. The same filters are sold by factor as ND2, ND4 and ND8. The app shows OD, STOPS or FACTOR.; 0.3 per stop
T-stop: An f-stop corrected for the light the lens really lets through. Cine lenses are marked in T-stops so two lenses at T2.8 give the same exposure. The app can show T-stops or f-stops.; T 2.8
Shutter angle: The shutter written as a share of each frame: 360° is the whole frame and 180° is half of it. At 24 fps, 180° is 1/48 of a second. The app shows the shutter as an ANGLE or a SPEED.; 180° at 24 fps = 1/48 s

The sun

Golden hour: When the sun sits between 6° above and 4° below the horizon: low, warm light that comes in from the side. It happens after sunrise and before sunset, and how long it lasts depends on the date and where you are.; −4° to +6°
Blue hour: When the sun is between 4° and 8° below the horizon, just before sunrise and just after sunset, and the sky carries the light.; −8° to −4°

In the app

REF: Pins the reading you are on as the reference. Point at another light and the REFERENCE card shows REF, NOW and the difference in kelvin, mired and tint, and ADD TO THIS LIGHT names the gel that closes the gap. MATCH shows when the two are within 5 mired.; REF · NOW · Δ
LOG: Keeps the reading with the frame you were pointing at. Hold LOG on the back wide camera for a RAW MEASUREMENT, taken from a RAW frame instead of the camera's white balance.
LIBRARY: Every reading you logged, as a contact sheet, newest first. Compare any two in mired, share one with its picture, or clear them all.; COMPARE · CLEAR ALL
HIGH, MEDIUM, LOW: The badge that says how settled the reading is. It reads LOW while the numbers are still moving, MEDIUM as they settle, then HIGH when the number is worth writing down. Library tiles shorten MEDIUM to MED.; HIGH · MEDIUM · LOW
DIFFICULT SOURCE: Shown with LOW when a RAW measurement and the camera's white balance disagree by more than 15 mired. It means a spiky light, like a cheap LED or a fluorescent tube, that no camera can pin down, and the app says so rather than making a number up.; RAW vs AWB > 15 mired

Gel numbers are LEE Filters' published mired shifts, the same table the app uses. Rosco's equivalents differ by a few mired.