Oral Health Group

Incandescent to Halogen to Diode: The Evolution of Visual Diagnostics

July 1, 2013
by Dr. Ira Hoffman DDS, FADI, FIADFE

Lighting technology has evolved dramatically over the past century. With the introduction of gas and incandescent lighting, dentists were finally able to shed some light on the teeth that they were treating. The illuminated visual access enhanced diagnosis and facilitated more precision in dental procedures. As the use of light-focusing bulbs and light-reflective surfaces matured, practitioners became highly dependent on external illumination, targeting specific areas in the mouth for visual inspection. More recently, halogen bulbs have gained popularity in the profession.

While modern incandescent and halogen light sources are both effective at illumination, they have the unpleasant side effect of heat production, generated by the infrared spectrum of the emitted radiation.1 Any patient or dentist who has come into direct physical contact with a “hot” light is familiar with the disagreeable consequences. The heat also tends to warm the operatory, pleasant in the winter perhaps, but much less so in the warmer seasons. If the operatory light (particularly the halogen variety) is positioned too close to the patient’s mouth, a long appointment can produce tissue desiccation (Fig. 1). The full spectrum lighting may emit rays in the UV range, which can be uncomfortable to the patient.


Incandescent and halogen bulbs also require rather regular maintenance and replacement. This is particularly problematic with halogen bulbs that can be contaminated by the oils on human skin; yet they require a very high level of manual dexterity to install into their oddly designed sockets. Changing halogen bulbs is always stressful, and not always successful. While practitioners recognized these problems, there were no better options available.

Over the past few years, Light Emitting Diodes (LEDs) have made major strides in replacing earlier, less efficient and less effective illumination sources in every conceivable application, dental and otherwise. In fact, dental polymerizing lights today are almost exclusively LED, a quantum change that took only five years to unfold in the normally conservative dental profession. The latest application for Light Emitting Diodes is the operatory light. LEDs eliminate the most serious drawback of halogen lights: the heat. The LED overhead light can be positioned centimeters away from the patient without causing discomfort or desiccation. The LED emission spectrum is very narrow and can be precisely controlled.

The LED is a miniature light source encased in a plastic lens2 (Fig. 2). A flow of electric current excites the electrons inside the diodes. This causes the solid-state semiconductor (no filaments to burn out) to release photons, producing a cold white light that generates no heat.3 The wavelength of the cold light produces greater illumination using far less power than traditional halogen lights. LEDs are very energy efficient, reducing power costs by as much as 85 percent. LED bulbs are rated at 50,000 hours; thus a full time practitioner will need to change them every 25 years or so.4 LEDs are very low (no) maintenance and contain no mercury or other toxic chemicals.

A recent optical study demonstrated that appropriate illumination could have positive biological effects on the human body.5 LEDs have been shown to increase alertness and reduce fatigue during long dental procedures. LEDs have been documented to have two separate effects on the brain; non-visual and visual.6

For visual effects, perceived images are created through a complex set of processes and interactions that occur in the visual cortex of the brain.5 Visual acuity is increased when the object is illuminated with a higher quality lighting source such as an LED.

For non-visual effects, specific brain processes such as biological rhythms, endocrine secretion, emotion management, alertness level and muscular tension are influenced by light emissions. Recent studies have shown that both light intensity and light temperature (or color) can manipulate non-visual effects.6

The G.Comm Polaris LED distributed by Flight Dental Systems (Toronto ON) incorporates the benefits of LED technology (Fig. 3). Unlike fixed color temperature halogens, these LED operatory lights can be controlled for both light intensity and color temperature, (Fig. 4) and are thus optimally adjustable for every practitioner and every situation. It is available in single track; dual track, ceiling mount and unit mount options.

The Polaris is the first LED light to offer a fully adjustable color temperature regulation system that allows the illumination to be adjusted from 4,200ºK (yellow-red) to 6,000ºK (daylight white) (Figs. 5, 6, 7). The LED operatory light is used for many different procedures, and the illuminating device must be flexible and accommodating for a variety of diagnostic procedures and clinical treatments.

Research has indicated that increasing color temperature during surgery increases operator concentration and alertness, in addition to providing an enhanced contrast environment for soft tissues.5 The Polaris color mixing technology allows practitioners to optimize the color temperature contrast for soft tissue operations. The contrast provides better visual acuity and a reduction in glare from oral cavity fluids.

The Color Rendering Index (CRI) of the light source is one of the most important determinants of lighting system quality.7 The CRI is a quantitative measurement of a light source’s ability to accurately reproduce colors objectively when compared to a natural light source. The higher the CRI, the more accurate the portrayal of the color as perceived by the eye.8 Thus, although lighting can increase visual acuity by brightness, the most important parameter is the viewer correctly perceiving the image as if in natural daylight. The Polaris LED light excels in the area of color rendering with a CRI of >90, allowing true colors to be seen as seen in natural daylight. The Polaris LED color-mixing feature can change the visual environment to a natural daylight color, making it ideal for avoiding metamerism in shade matching.

The Polaris LED is the first operatory light with fully adjustable intensity controls from 8,000-35,000 lux. At the lower levels, the inadvertent photo-polymerization of composites is minimal (Fig. 8). At the higher levels, visual acuity is improved BUT visual fatigue increases, as well (Figs. 9, 10). The required level of illumination may vary from one practitioner to another, from one procedure to another, and based upon the operator’s alertness, from one part of the day to another.

The 8,000-35,000 lux range was selected to provide flexible lighting intensity, with full spectrum adjustment control, that would optimally suit individual needs and requirements at a safe intensity without glare or visual discomfort for patient or dentist.

The Italian design inspired Polaris LED has unique features that produce a high quality light, taking into consideration the latest scientific studies on the effects and benefits of various illumination parameters. OH

Dr. Ira Hoffman maintains a private practice in Montreal Ontario. A graduate of McGill University he is a Faculty Lecturer, Clinical Supervisor in the Department of Restorative Dentistry at McGill University. He is on the edito
rial board. Dr. Hoffman is a member of the University Advisory Council of the American Academy of Cosmetic Dentistry and acting chair of the University Coordination Committee of the Canadian Academy of Esthetic Dentistry. Dr. Hoffman is a Fellow of the Academy of Dentistry International and the International Academy for Dental Facial Esthetics.

Oral Health welcomes this original article.


1. Eisenbaum, S.L. (1989). Facial Burns as a Complication of Office Surgery Lighting. Plastic and Reconstructive Surgery. 83, 1, 155-159

2. Schubert, E. F., Gessmann, T., & Kim, J.K. (2001).Light Emitting Diodes. Kirk-Othmer Encyclopedia of Chemical Technology.

3. Holonyak, N. (2001). Is the light emitting diode (LED) an ultimate lamp?. Am. J. Phys., vol. 68, pp.864 -866 2000.

4. Kramer, M.R., Shchekin, O.B., Mueller-Mach, R., Mueller, G.O., Ling, Z., Harbers, G., & Craford, M.G. (2007). Status and Future of High-Power Light-Emitting Diodes for Solid- State Lighting. Journal of Display Technology, Vol. 3, 2, 160-175.

5. Cajochen, C. (2007). Alerting Effects of light. Sleeping Medicine Reviews. Volume 11, 6, 453-464.

6. Webb, A.R. (2006). Considerations for lighting in the built environment: Non-visual effects of light. Energy and Buidlings. 38, 721-727.

7. Kimura, N., Sakuma, K., S., Asano, K., & Hirosaki, N. (2007). Extrahigh colour Rendering White light-emitt ing diode lamps using oxynitride and nitride phosphors excited by blue light-emitting diode. Applied Physics Letters. 90, 5, 51109-051109-3.

8. Sommer, C., Krenn, J., Hartmann, P., Pachler, P., Schweighart, M., Tasch, S., & Wenzl, F. (2009). The Effect of the Phosphor Particle Sizes on the Angular Homogeneity of Phosphor-Converted High-Power White LED Light Sources. Selected Topics in Quantum Electronics. Volume: 15, 4, 1181 – 1188.