Photography and cinematography use similar lighting technologies, including:
- Hydrargyrum Medium-arc Iodide (HMI)
Lights always produce both light and heat. Since the goal is to light and not heat the subject, a good light to heat ratio is therefore one of the main criteria in choosing between technologies. This is fundamental in cramped studio settings, where an overly hot environment would otherwise be unhealthy and distracting.
Another important criteria when purchasing lights is the light intensity to power ratio, in other words, the amount of light provided per watt. As electrical consumption is generally proportional to luminous flux for the same technology, cinematographers and photographers will often select lights for different needs according to their power ratings.
LEDs, or light emitting diodes, are made of a semiconductor material that releases photons when a current is applied. The technology is at the cutting edge of the lighting sector, with the main reasons the market is moving in this direction including their:
- Reduced electrical consumption and higher efficiency.
- Lower heat emission, due to reduced infrared wavelengths.
- Extremely long lifecycles, typically over 30,000 hours of use.
- Tendency to fade rather than blow out when exceeding lifecycles, if well-manufactured.
- Compactness and reduced weight compared to traditional filament and gas lighting.
- Color temperature profiles that remain almost unchanged for their entire lifecycles.
- Light quality, in terms of color rendering, very similar to sunlight.
We might, indeed, call them the ‘El Dorado’ of studio lighting, and it is reasonable to think they will replace all other photographic and cinematographic lighting technologies on the market within a few years. However, not all LED lights are equal.
A LED from the manufacturer Mole-Richardson
To be fully aware of what you are buying, you need to know the kind of LED used and how it is supplied with electrically, since identical-looking lights may actually have very different technical characteristics, which we will consider below.
First and second generations
Let’s start with the most visible difference, clearly seen in the following images. Older first-generation LEDs have a match-head shaped bulb, while newer, more efficient, second-generation LEDs, often called Chip-On-Board, or COB, LEDs, are made up of a phosphor-coated diode matrix, and are the most suitable for professional lighting.
A first-generation LED and a second-generation COB-type matrix LED
Luminous efficacy: lumens per watt
Knowing how many lumens per watt the light source can provide is fundamental, so do check the manufacturer’s specifications. Also use a goniophotometer, spectrometer, or light meter, to double check, since manufacturers tend to rather overestimate values. Lights, and even LEDs, with the same nominal consumption in watts, can vary by as much 50 to 150 lumens per watt in effective luminous efficacy, which makes for a huge difference in the resulting lighting.
Color Rendering Index
The general principle that the color white is made up of different color frequencies in the visible spectrum also holds for LEDs. With a balance of colors across the continuous spectrum of wavelengths, sunlight has the highest color rendering index (CRI), while phosphor-coated LEDs generally have a CRI varying from around 85 to 97, out of the maximum of 100. At the time of writing, some manufacturers have even begun to market LEDs with CRIs close to 99, but these are not yet powerful enough for stage and studio applications.
Light emitted by a source other than the sun may appear perfectly white to the naked eye, but may have a different hue when captured by a camera. The three most problematic wavelengths are those of colors blue, red and brown. This means that brown skin, for example, may vary significantly in hue when lit by different LEDs, and the same goes for blue and red objects. The difference between a CRI of, for example, 88 and 95 is clearly perceptible in results using the same equipment.
An important consideration to keep in mind when choosing a light is the relationship between luminous efficacy and color temperature consistency and precision. As consistency and precision increase, the ratio between lumens and watts decreases and worsens. LEDs with CRIs above 90 produce accurate lighting and video results, but have lower light emissions than light sources with CRIs in the 70s or 80s, while high-end LEDs may have an efficacy of more than 100 lumens per watt, pushing the upper threshold to around 150 at the time of writing. The most modern technologies can achieve a CRI greater than 90 with calibrated color temperatures and a balanced color range perfect for photographic lighting, studio lighting and video lighting. Lights with a color temperature of 6000K and a CRI of 80, for example, are less accurate than LED arrays designed for the photographic studio and calibrated at 5600K with a CRI of 90, 95 or even more, while offering a 20 to 30% higher light efficacy per watt. In case of uncalibrated color temperatures, filters or jellies can easily be used to re-centre the color profile on a specific temperature, for example, 5600K. On the other hand, if you start with a poor CRI, it is more difficult to do anything to change it. Today, with raw image files, the digital equivalent of negatives, you can correct imperfections in post-production. However, if the color temperature is precise, and CRI is high, then it takes less time to adjust colors, since they already start off relatively more balanced. This is an important aspect to consider, especially when working with light sources from different manufacturers.
Spot and Flood
Similarly to other lights, LEDs can be used in spot, narrow beam, flood and wide beam modes, with variable optics that focus their largely 180° arcs. It is wise to check manufacturer’s specs, which almost always indicate minimum and maximum angles. Generally, LEDs emit light in the forward direction only, so there is no need for an internal parabolic reflector, simply a truncated cone reflector with a Fresnel lens in front.
One of the most essential components to look for in a modern light is a Digital Multiplex (DMX) controller, which allows you to dim the light from 100 to 0% by remote control via a cable similar to those used in high-end hi-fi systems (with an XLR connector). It is inadvisable to purchase a light that does not have a DMX controller, or cannot be fitted with one later.
Wi-Fi and Bluetooth
The opportunity to control your light remotely should not be overlooked. Today, it may still seem an optional, but it soon seems set to become a must. So consider very carefully the purchase of any light without one of the control methods of Wi-Fi or Bluetooth. If you can choose, Wi-Fi is preferable, as it has a wider range of applications and creates a network for multiple device management, instead of a simple point-to-point connection between the controller and one device.
Android or iPhone app
There are no great differences between the two platforms, though the app should be able to work on both tablet and smartphone. For television studio lighting, the remote control feature is particularly useful, since climbing a ladder to adjust a large number of individual lights is impractical. App control is thus essential, unless you want to use more traditional DMX-type wired connections.
An integrated touchscreen, allowing you to make quick, easy adjustments, is an extremely useful option.
Water-resistance is often an overlooked option, though the need to shoot in light to heavy rain or even underwater is not uncommon. For this reason, check for water-resistance, which is often indicated with an IP rating in the manufacturer’s instruction manual or on the light itself.
Customer care will get you out of trouble if your light has issues or needs to be repaired. Repair or replacement times are one of the main criteria to consider, as even a day’s delay can be critical when working to a deadline.
In conclusion, these are just some of the criteria that should influence your purchase. Other criteria deserve chapters of their own, as does a discussion of specific light brands and manufacturers.
Bright Hydrargyrum Medium-arc Iodide lights, or HMIs, still in use, have high 60 to 80 lumens per watt efficacies. HMI bulbs contain a mixture of mercury and halide gases, with H standing for hydrogen, M for metal halides and I for iodine. Some past models also used bromine. As bulbs may break or sometimes explode, they are legally required to have some sort of protection, such as metal netting.
HMI from the manufacturer ARRI
To light such a bulb, an arc must be created between two electrodes in order to pre-heat the gas within. This requires a high voltage, an electrical component called ‘ballast’, and grounding, which can be difficult to achieve when shooting outdoors. The ballast simply transforms the voltage from 110V or 220V, depending on which part of the world you are in, into about 10,000V for the period of time necessary to trigger the bulb arc.
One advantage of HMIs is their continuous light spectrum, while a major disadvantage is the relatively long time (10 to 15 minutes) they need to reach their nominal color temperature. Common power ratings, proportional to luminous flux, are 575, 1.2k, 2.5k, 4k, 6k, 8k, 12k and 18k watts.
The great value of HMIs lies in their high light intensity, even if today’s LED lamps have greater efficacies. Apart from this, the list of disadvantages goes on. Ballast, in addition to needing grounding, is generally heavy and cumbersome, must be kept constantly dry, leaks voltage over time, and, as if that were not enough, must be kept close to the light, as an overly long cable presents a fire risk. What’s more, bulbs break easily, need 20 minutes to cool before being turned on again, last for only about 700 hours, and have relatively high costs (~$100 for a 1200W bulb).
Bulbs containing xenon gas, following the principle of HMI lights, also require ballast, though they have a higher luminous flux, at around 150 lumens per watt. In photography, they are no longer used for steady but rather flash lighting. They have a parabolic reflector and are almost always used in spot positions.
Carbon arc lights
Carbon-arc bulbs require a high voltage arc to be maintained between two carbon electrodes. They were commonly used in movie-making, as they represented an excellent compromise as a fill light when the sun was used as key light. Now out of production, they can sometimes still be rented.
Carbon-arc light from the manufacturer Mole-Richardson
These lights were once widely used for their carbon or tungsten quality daylight. However, they emitted a significant amount of ultraviolet radiation, known to have damaged the eyesight of several famous actors. Their arcs were difficult to control and their bulbs burnt out easily.
Studio tungsten lights, contain a tungsten filament heated by electric current, similar to traditional household bulbs, and were used up to only a few years ago. Most have a parabolic reflector behind the bulb, and, in such cases, are also called ‘pars’.
Tungsten filament lamp
By moving a knob, the bulb is moved towards or away from the parabolic reflector, generating a spot or flood light effect. Tungsten lamps also come in a variety of wattages, generally 200, 500, 750, 1K, 2K, 5K and 10K, depending on the manufacturer. Pars are often mounted in arrays, called ‘brutes’ or ‘dinos’, according to the shape of the array, and are still used, especially for movie lighting.
Neon lights also use gas, and produce a particularly soft lighting, which can have either a warm (3200K) or cool (5600K) daylight or tungsten color temperature, indicated by a blue circle near their sockets. They are often used in studio lighting to soften outlines and shadows, and eliminate subject imperfections. They come in two different standard lengths and banks of 4 or 6 bulbs.
The main issue with these lights is the flickering that can seen in some video recordings. This is because neon lighting flickers at 50 Hz, and, if you record at 25 frames per second with a shutter speed of around 1/50 of a second, it will match the frequency of the flickering. Technically, we can synchronize the lamp with the camera to eliminate the effect. However, if, by necessity, we set the camera to 60 frames per second, we would have a shutter speed of 1/60, and would surely notice the effect. In short, it is clear that neon lights are not suitable for high-speed shooting.