LED lighting. Good for some cases, but not all.
LED lighting. Good for some cases, but not all.
We are seeing a lot of LED lighting products in the entertainment lighitng industry. Reallly high brightness LEDs at the current state of the art are typically being overdriven. So that 100000 hour lifespan is gonna drop a decimal place or two when they get installed on planet reality. This is compensated by having large arrays of LEDs on a circuit board backed up by a really large heat sink and in some cases, active cooling measures such as fans or heat pumps to keep that component killing heat away.
One early adopter of LEDs are in traffic signals. Next time you are driving, observe the led lamps in the traffic signals and on motor vehicle tail lamps. You will notice segments of leds that are dead. Because when one LED dies, it blocks the current for the other LEDs in it's local circuit, usually this is five to seven individual LEDs. These traffic signal lamps are also usually overdriven to produce the light output desired. Note also that these traffic signal lamps are not always on, so they get a cooling off period which increases their life.
YOu are also not going to get the advertised lumens per watt out of these fixtures for very long, if at all. LEDs will dim over their lifespan, as much as 50% less at end of specified life. Reputable LED manufacturers will specify a light output it will output after it's burn-in period and when it is not being overdriven. You also get more efficiency loss in the power supply in the fixture. Salesweasels will measure the output of a brand new fixture at six inches or so, and quote this figure in their proposals being a little vague about it.
Another problem that is not really an issue for a parking lot, but is a big issue in other areas is color temperature and color rendering index (CRI). If someone wants LED lighting indoors, this is a gotcha that leads of difficult to diagnose and unfixable problems. Think the difference between cool white, warm white and plant growing flourescent tubes.
If you need the very long lamp life, and can live with the lower levels of light, or compensate by increasing the fixture count, then go for it, and get units that you can put into a long life or economy mode. Otherwise I'd stick with one of the standard fixture types. Look at life cycle costs, not just install costs.
LEDs are great for things like exit signs, fire escape stairwell tread lighting, and of course colorful decorative things. For general illumination, not really ready for prime time, but getting close. In a couple of years, who knows. State of the art in LEDs is a pretty fast moving target right now.