| LASER | Used by surgeons as an alternative to a scalpel. Cuts and coagulates vessels (lessens bleeding) at the same time. |
| LASER ASSISTED UPPP (LAUP) | Fancy version of a conventional UPPP but unlikely to be any better. |
| Laser assisted uvulopalatoplasty (LAUP) | Can eliminate or decrease snoring but has not been shown to be effective in the treatment of sleep apnea. |
| LAUP | Laser assisted uvulopalatoplasty |
| Leg Movement | Leg movements are recorded in both diagnostic sleep studies and titration studies. |
| Letter of Medical Necessity (LMN) | Certification by a physician that the prescribed item(s) is/are medically indicated reasonable and necessary with reference to the standards of medical practice and treatment of a patient's condition. |
| Light Sleep | Term used to describe non-REM sleep stage 1 and sometimes stage 2. |
| Light Therapy | Used in the treatment of SAD (Seasonal Affective Disorder) and other conditions. Exposes the eyes to light of appropriate intensity and duration and at the appropriate time of day to effect the timing duration and quality of sleep. |
| Light-Dark Cycle | Periodic pattern of light (artificial or natural) alternating with darkness. |
| Limit-Setting Sleep Disorder | Disorder due to childs difficulty in falling asleep by delaying and refusing to go to bed. |
| Linear Sleepiness Rating Scale | Measure of subjective sleepiness. The scale contains a horizontal line 100 mm in length - the right extreme is labeled "Very Sleepy" and the left extreme is labeled "Very Wide Awake." |
| LMN | Letter of Medical Necessity |
| LO | Lights Out (beginning of sleep recording) |
| LTD | Long Term Disability |
