HMI appearing green?

[Raymond Zrike]

We shot a 1.2k HMI (fresnel) through a window during the day. We gelled the window with full CTO (LEE Filters I believe) and shot on 200T s16. Why does the light through the window appear green? It’s not what I expected, but I also don’t have very much experience with HMIs. The other lights in the scene are LiteMat 4s set to 3200k.

Above is a scan from Kodak NY with a ScanStation. I threw on a very basic grade.

[Mark Dunn]

Non-expert here.

When I pull it into Lightroom and white balance on the white pipe, it reads as not so much green as very deficient in blue- something like R66, G67, B42%. The original does look quite green but it's not so noticeable when corrected. Lightroom puts a substantial magenta tint on it.

I wonder if it's an effect of the mixed daylight/gelled HMI. Or it just looks green beside the warm colour of the wood and her jumper.

Edited August 27, 2023 by Mark Dunn

[Raymond Zrike]

I think the light is actually green based on this quick correction I attempted.

Here is the original:

Here is the correction:

While everything in the shot looks fine, you can see that the green marker on the slate has completed shifted along with the HMI light.

5 hours ago, Mark Dunn said:

I wonder if it's an effect of the mixed daylight/gelled HMI.

I had that thought too, though the daylight was gelled just the same as the HMI since the window was gelled rather than the HMI itself.

5 hours ago, Mark Dunn said:

it reads as not so much green as very deficient in blue- something like R66, G67, B42%

I'll try adding blue.

We might end up leaning into the green daylight for these shots anyway. It's a fantastical film where the outside world is supposed to be hazardous. But it'd still be nice to know what is going on exactly.

[Joshua Cadmium]

Maybe the bulb wasn't on long enough to settle, or the bulb was old, or the ballast was dimmed (which can cause a green shift): https://lightbulbrentals.com/hmi-troubleshooting/ .

HMIs are also just a little finicky in general and may need to be gelled with plus or minus green in order to hit a neutral white.

[Raymond Zrike]

52 minutes ago, Joshua Cadmium said:

Maybe the bulb wasn't on long enough to settle, or the bulb was old, or the ballast was dimmed (which can cause a green shift): https://lightbulbrentals.com/hmi-troubleshooting/ .

HMIs are also just a little finicky in general and may need to be gelled with plus or minus green in order to hit a neutral white.

All of those could very well be the explanation. Thank you! I'll make sure to have some magenta gels on hand next time. We'll just have to embrace the green for these shots haha

[Aapo Lettinen]

old bulb on the hmi would be the easiest explanation, they can be so green that it is noticeable with bare eye and it is common for them to turn green if just old enough. Usually at that point the glass on the bulb is eroded and faded noticeably and is not clear anymore so they are easy to spot if checking the bulb.

I have a habit of opening every HMI unit regularly to visually check the condition of the bulb and it needs to be done at least at the start of the production and if the unit has not been used by your crew before. Especially used hmi's on sale can have really nasty and unusable greenish bulbs with eroded electrodes and can even be on the edge of blowing up.

Generally speaking, if the bulb's glass cavity looks completely transparent and clear, then it is often fine, being either new-ish or at least low enough hours to be pretty great condition. And if it is hazy and/or eroded, it is likely not usable anymore, at least if wanting it working reliably and with good colors

[Adrian Sierkowski]

It's most likely the bulb being too old. Generally, before I went to mostly LEDs, we would color meter each HMI at the start of a show and make up it's correction pack to get it to 5600 and not be green (or purple).