Lensing your Light: Continuous lighting and the Fresnel lens

With the increase in resolution and speed of today¡¯s cameras and the availability of lightweight fixtures that emit torrents of light, it becomes easy to forget about the different quality of light available to us when crafting images. This is a shame, as limiting yourself to only one kind of lighting unit can greatly impact the kinds of images that you can shoot. In this article, we will discuss the Fresnel (pronounced freh-NELL) light units, focusing on the ikan Helia HF40, which is a bi-color Fresnel lighting unit.
Continuous Light versus Strobes and the Sun
Depending on whether you are discussing stills / photo or video / motion, the term continuous lighting has different meanings. In the still¨Cphoto world the word ¡°continuous¡± refers to light units that are not strobes, and are also known as hot lights (tungsten lights), which do not strobe. Photo strobes often have low-power ¡°modeling¡± lights that allow the photographer to see the effect of the light unit on the model, and then fires a strobe when taking the picture, providing an extremely bright, short flash of light. The advantage of this is that you can light your subject without your light fixtures wilting your subjects. However, for some shoots, still photographers will use so-called ¡°hot lights,¡± which are just light units with tungsten¨Chalogen bulbs behind a Fresnel lens, which would be found in many a film or video studio. These tungsten¨Chalogen lights produce a beautiful quality of light, but also a tremendous amount of heat.
When discussing video / motion lighting, the term continuous lighting has a significantly different meaning. Both the sun and tungsten lights are considered to be continuous light sources, which provide the full spectrum of the frequencies of light. Sunlight does contain more blue than tungsten light, hence the higher color temperature of sunlight compared to tungsten, but they both provide the full spectrum of visible light. Fluorescent, LED, and Plasma lighting are what is known as correlated light sources, which mean that they provide an approximation of the full spectrum of light, while missing varying frequencies, depending on which manufacturer makes the bulb. It is just something you want to keep in mind while choosing between fixtures, be certain as to whether it is a fixture for still photos or video.

Incandescant (tungsten) light: Full spectrum

ikan Helia HF-40 at 3400K, correlated light source

The Fresnel
Fresnel lighting has been around for a long time, and for many years it was the staple of the motion picture industry. The Fresnel lens is essentially a lens that has been carved out, to provide light control¡ªflood and spot, projecting a beam of light, without projecting the filament of the light bulb itself. Because the lens only has to transmit light and not an image, the lens can be made lighter by carving out sections of the lens, essentially compressing the lens, making it less thick and thus saving tremendous amounts of weight. What this provides is a spot/flood adjustable light with a desirable quality.

The majority of Fresnel fixtures use tungsten halogen bulbs, and can vary from small lenses only a few inches in diameter to lighting units with lenses more than a foot in diameter or larger. Owing to the inefficient nature of tungsten bulbs, these fixtures throw off a lot of heat, and can become very tricky to operate. Additionally, the larger the bulb, the larger the light fixture you need. They will also draw a lot of power compared to LED lights for the amount of light they produce. However, it is the quality and control of the light that make Fresnel lights so useful. Fresnel lenses emit a light that is not quite as hard as a bare bulb. By ¡°hard,¡± I¡¯m referring to the shadow that the light fixture renders. Bare bulbs cast?a very dark shadow, with sharp edges, while highly diffused or ¡°soft¡± lights render a less-defined shadow with soft edges. Fresnel-lensed light falls somewhere between the two. Of course, with all light units, the farther away from the subject, the sharper the shadow will be, but at equal distances the light units behave as above. So Fresnel lights are extremely useful, as they are less harsh than bare bulbs, and provide what many people?feel is very flattering light on a subject¡¯s face. In addition, they are very punchy, which allows you to add diffusion to taste, while still maintaining a decent exposure. Another great use is to cast shadows and patterns, something that LED-array lighting units don’t do quite as well.
Fluorescent Lights and LEDs
Fluorescent lights are correlated light sources, and household lights usually have a slow flicker rate, which can create flicker in your exposure, as well as?strange color shifts. The first problem that was solved with fluorescent lights was the color temperature, with bulb manufacturers creating special blends to make florescent bulbs that were closer to tungsten or daylight balanced, while minimizing the green spike in the florescent light¡¯s spectrum. Then Kino Flo came out with a ballast that flickered at an astonishing 250,000 Hz, providing an essentially flicker-free light source, with bulbs formulated to work specifically with the?company’s ballasts. The Kino Flo lights brought a very sourceless style of lighting to filmmaking, especially popular in interview settings.
Battery-powered LED arrays quickly became popular as lightweight, long-lasting alternatives to tungsten-halogen on-camera lights, bringing lower temperatures and longer battery life. The popularity of the on-camera lights quickly led to the development of larger arrays, which provided a similar but not quite sourceless light. The weaknesses of the early LED array lights were both in color reproduction and the beam pattern cast by the array of point sources. However, in spite of the fact that LED bulbs were originally not able to provide a strong enough output, unless used in an array, the fact that they could be powered by?batteries for long periods of time while generating little heat made them very popular.
A small ¡°Mini Mole¡± Tungsten Halogen Fresnel, on the left of the frame, and the Helia HF-40, on the right, with both fixtures set to full spot. The Mini Mole has a smaller lens, and smaller beam diameter. The Helia has a very even spread and, with the Helia set to 3400K, you can see the light is a good match for the tungsten-halogen bulb.?
LED Meets Fresnel
Fresnel LED lights came kind of late to the party, but are becoming increasingly available and flexible. The advantages of Fresnel LED fixtures over traditional tungsten-halogen Fresnel units are in heat generated, color-temperature flexibility, and weight. One of the newest entries in the LED Fresnel field is the ikan Helia HF-40. I recently worked with the three light kit, and used them alongside some older tungsten Fresnel lights for an article on five-point lighting. As the HF-40 is a bi-color unit, with color temperature variable from 2700 to 5600K, I set the units to 3400K, which by eye, matched the tungsten unit¡¯s color temperature. I also found the HF-40 to be about equivalent in output to a Fresnel light that uses a 200¨CWatt AC bulb (FEV), while only drawing about 40 Watts. This is a pretty significant power savings, and allows you to power this light with AC power?or battery power via a P-Tap / D-Tap or a V-mount battery, thanks to the included V-mount plate that mounts directly on the light¡¯s Yoke.
The V-mount battery plate is mounted on the Helia¡¯s yoke,?avoiding dangling power cables while?allowing you to?power the light from a V-mount battery without impacting the range of motion of the light.?
As I wrote, the light draws approximately 40 Watts, but what I found to be even more significant is the lack of heat produced. After ten hours of continual use, the light HF40 was barely warm to the touch, easy to handle and adjust, compared to the tungsten-halogen Fresnel, which quickly became too hot to touch without using a leather palm glove. Even using a glove, tungsten-halogen lights become unbearably hot very quickly. Just imagine how many burned fingers could be avoided using LED Fresnel lights, not to mention lower air-conditioning costs, or the toll that is exacted on your talent and crew when working on broiling-hot sets. The HF-40 fixture itself is very well designed, compact, and with the LED light source generating comparatively little heat, the HF-40 can utilize a lightweight acrylic lens instead of a much heavier thermal glass lens. This saves not only on weight, but cost as well, as anyone who has had to replace a glass Fresnel lens can attest. That doesn¡¯t mean that the LED doesn¡¯t generate heat¡ªit does¡ªbut the HF-40 incorporates a fan to aid in cooling. Don¡¯t worry; the fan is so quiet that only a sound recordist with the mic right up against the fan would be able to hear it, so no problem with recording dialog.
As far as quality of the light, I found that after years of using fluorescent lights, with their sourceless effect, it was a pleasure to go back to using a Fresnel light, which is far more controllable and in many ways more flexible than a fluorescent light. For example, the HF-40 provided a strong key, and it is compatible with many 5″ accessories, such as snoots, scrims, and speed rings for soft boxes; pretty much anything you can use with an ARRI 300 Plus will fit.
The fixture produces a light that is strong and punchy, while still nice on the face, and as with traditional Fresnel lights, it provides enough light to effectively diffuse without killing the output. The lower heat emitted by LED fixtures will also extend the life of your gels, although with the variable color temperature of the HF-40, you can skip color-correction gels, and the loss of light that goes with using them. In addition to the variable color temperature, the fixtures can be dimmed from 100 to 0% brightness without flickering, and with only minimal color drift. There is also a strobe setting, which is not for taking still photos, but rather for creating a strobe-lighting effect without requiring a flicker box or shutter system.
The three-fixture kit is a complete package in an extremely rugged and heavy rolling case. But the case protects the electronics of the fixtures, so it is an unfortunate necessity. I was originally skeptical of the included kit stands, but in spite of their small size and footprint, they provided good height, and were able to support the fixtures, even after I attached a chimera that I had borrowed. The lights stayed well balanced on the stands, but you will definitely feel more comfortable using a sand bag to steady your stands, especially at maximum height.
Here, a Chimera softbox is mounted on the Helia HF-40. You can see how well the Helia¡¯s beam covers the softbox¡¯s diffusion panel.?
The HF-40 works really well. It has a smooth spot-flood mechanism, even beam spread, and is a good bellwether for the future of LED Fresnel lighting. It provides a strong source light that can be cut nicely with a flag or cookie, looks good on the face when used directly, and it takes well to diffusion or softboxes¡ªall the performance you would expect to get from a Fresnel light, without the heat and weight. So, if you haven¡¯t worked with Fresnel lights, what are you waiting for? They are extremely versatile, and provide a quality of light that fluorescents and LED array lights can¡¯t match, while still allowing you to soften the light if that is the look you desire.