HMI

What this is about

When a scene has to hold against the sun — an actor in a doorway at noon, a car interior against a bright street, a window pushed from outside — an HMI is usually the answer. The cost is infrastructure: a head, a separate ballast, a heavy cable between them, and enough power that a generator often comes along. Bulbs are expensive and the lamp needs a few minutes to reach full output and stable color, so the schedule has to allow for a warm-up.

A term only helps when everyone on set means the same thing by it — so what follows is how it is used, not a dictionary definition.

What runs differently here

Where this differs from the general case:

• An HMI runs at daylight balance out of the box, which is why it needs no blue gel against the sky.
• Head and ballast are two separate items with a cable between them; both take space and both go on the order.
• Older magnetic ballasts can flicker at unusual frame rates, so a high-speed shot needs a flicker-free electronic one.

With TillyGen

TillyGen's equipment list keeps head, ballast and power together, and the schedule holds warm-up time so the first take is not lit at half output.

Change one constraint and the consequences travel through the whole plan: affected shots are flagged, the call sheet is regenerated, and nobody keeps working from yesterday's version.