Why use Big Studio/Film Lights?
There is a reason why big budget film sets look the way they do. Making an indoor film set look realistic or a night exterior exposed enough is only possible with high luminescence and focused light. Photometry also plays a big role because the stronger and further the throw of the light, the more natural it becomes.
(4) 20K Mole beam coming back from a job
The stronger the light source, the inverse square law becomes less evident in the light fall-off, meaning the brightness difference between two distances of the light is less than that of smaller light source. The further the light, the less lumen difference is between two distances on the set.
Using Arri's Photometric App:
Since Arrimax (18K HMI) is a very bright light, it can get good exposure being far away. To achieve 1,000 lux (Which at 800 ISO, 24fps, 180Shutter is at F8.0), the light needs to be at 31.54 meters (flooded).
- The light is 30 meters away from the window outside of the set
- The set is 10 meters in length from where the light source (window) will come through. So near the window inside the set would be 30 meters from the light, whereas the opposite end of the film set is at 40m from the light.
Light: Arrimax (18,000 Watts) (spot)
Distance at 30 meters in Lumens: 1106
Distance at 40 meters in Lumens: 622
Difference in percentage: 78%
Film Terms: Dynamic range of F9 (at 30m) to F6.3 (at 40m), about ONE stop difference
Light: Arri M18 (1,800 Watts) (spot)
For an Arri M18, to achieve 1,000 the light needs to be at 9.27 meters (spotted)
Distance at 10 meters in Lumens: 860
DIstance at 20 meters in lumens: 215
Difference in percentage: 300%
Film Term: Dynamic range of F7 (at 10m) to F3.6 (at 20m), about TWO stops difference.
The brighter the light and the further it can be, the more natural the light will be. You can achieve similar looks using the ArriMax with the M18 by controlling the size of the set. A huge set like a big cathedral or the Grand Central Station, need an Arrimax or an array of Arrimax to achieve the daylight look. A house kitchen can achieve the same daylight look with an M18 as with a huge set with an Arrimax.
One big light can do the work of many smaller lights.
One of my favorite cinematographer, Sven Nykvist is the master of creating natural light on a set. His philosophy is using one light source as much as possible because the bigger the spread and the more powerful intensity, the more realistic it looks. He was a big fan of soft bounced light and using big source units. He valued simplicity in lighting, using only as little lights as possible.
Cries and Whispers, dir. Ingmar Bergman, 1972. DP. Sven Nykvist
With films doing big sets and shooting night exterior wide shots, only the big powerful HMI light, so far, can meet the needs of big spread and "natural look". ("Natural," meaning in the normal standards of film lighting developed throughout the years. A night exterior scene in films will not look the same as in real life.)
18K HMI Lights
Advantage of HMI
The advantages of HMI units are the brightness, daylight color temperature, and better power efficiency than Tungsten units. They are the workhorse of the film industry regarding high focused brightness. HMIs are the only high intensity daylight balanced light reliable enough for film use (There is also plasma light with good power efficiency but it operates at a bluer color than HMIs). If you want to achieve daylight color in Tungsten units, you would need CTB (Color temperature Blue), in return your left with 3x less intensity. In regards to power efficiency, it requires less power than Tungsten to provide a higher brightness level. A 24K Tungsten at 40m Flooded is 326 lux. 18K HMI (ARRIMAX) at 40m Flooded is 622 lux.
Disadvantage of HMI
The disadvantages of HMIs are emission of UV rays, color shift over time, frequency problems, and ergonomics. I believe the advantage of HMIs outweighs the disadvantage. HMI bulbs emits UV rays which with prolonged exposure can cause skin cancer. There is a UV filter on the lens of the light, so it is unwise to operate the light with a broken lens. As the bulb gets older the color shift to magenta or green becomes evident. There are gels to fix this problem so be prepared with them when operating HMI lamps. Another disadvantage is slowly being resolved with electronic ballast which is flicker problem. Try to rent an electronic ballast that has flicker free mode. Avoid magnetic ballast. And the last disadvantage is its ergonomics compared to Tungsten units. An HMI requires a header cable and a ballast, which means its takes longer to quality check an HMI unit when the problem can come from many different sources. It is good to know the disadvantages so you are prepared to fix the problems or know its limitations.
HMIs are used for daylight balanced cameras as it preserves the true color of the set. They are used to emulate mid-day light or moonlight: being used a mid-day sun source (Key light), adding fill on a bright sunny day, or lighting a night exterior. On big sets, you usually see these as an array, to give the cinematographer the exposure he/she needs.
Other HMI bulb wattages: 18k, 12k, 9k, 6k, 4K, 2.5K, 1.8K, 1.2K, 800, 400, 200, 125.
HMI lights are the brightest lights used mostly on film sets. They have the best brightness to power ratio, besides LED which still can't achieve HMI's brightness levels. Another big light that requires high wattage and output - not as much as the HMI bulbs - is the Tungsten 24K and 20K lights.
20K Mole beam at 20% intensity
Advantage of Tungsten
These lights are extremely hot and very bright. The few advantages of Tungsten lights over HMI lights are the better color quality (Tungsten being 100 CRI, while HMI is about 90 CRI), and its continuous light source - at high frame rate slow motion, HMI can have flickering effect while tungsten will never have flicker problem.
Disadvantage of Tungsten
Since Tungsten light is from a black bodied emmiter, it requires a lot of power to achieve its color and specific bulb brightness. About 90% of energy of Tungsten bulb is converted to heat and only 10% is converted to light. HMI bulbs are more efficient in transferring energy as light, making it brighter than Tungsten bulbs.
20ks and 24ks are used similarly as the 18K HMIs. The only reasons to use Tungsten over HMI, is the rich color quality and the orange color of the light. Tungsten is best used to achieve a dawn and dusk look, "The golden hour." These lights are also used for high frame rate filming, although HMI now has flicker-free option.
In conclusion, these big wattage lights will be the power horse of the film industry for many years to come because they offer brightness and throw (distance of well exposed light from the unit) that no other lights can - not even LED lights with its emerging popularity and technological advancements.
If you are starting in learning about film or starting to become active on professional sets, please be cautious and don't operate these lights. With their dangerously high wattage, there are very important skills and knowledge needed to operate these units. Always learn from a more experienced electrician, but also study the basics of electricity and proper use of the lights through Harry C. Box's Set Lighting Technician Handbook, so you are more prepared to know if you mentor is practicing bad procedures.
Level Nine Productions