FAQ on LED-based light bulbs

Q. What are the most salient parameters of a light bulb?
A. People buy a light bulb to get light! Smart people want to get a given amount of light at the least cost. Wise people consider the cost of lighting over time. Thus the key parameters of a light bulb are its light output in lumens, its power consumption in watts, its life in hours, its total cost of acquisition, installation and eventual replacement, and nowadays, its impact on the environment (due to mercury content of CFL and fluorescent tubes and their ballasts, and in general power consumption, waste disposal, the amount of raw material and energy consumed to make the product). All those factors are tied together in a spreadsheet available from PearlLED.com. LED-based light bulbs have been identified as the coming generation of light bulbs due to their highest light output per watt (input) and their very long life. But not all LED-based light bulbs are equal in those key parameters. The math in the spreadsheet helps the user select the best light bulb for each application. No, LED bulbs are not the best choice in every application. They certainly are the best choice in applications where they’re turned on for long periods such as 8 hours a day, used in hard to reach locations, and in off-grid living.

Q. What to look for in an LED light bulb?
A. First figure out the light output you need, by assessing your current illumination level based on extant light bulbs you use, typically 700-1500 lumens per bulb. Look first for a LED bulb that is rated for that minimum lumens, then look for its power factor (>0.9), its light distribution pattern (light cone, glare or no glare), its color or color temperature and its color rendering index, dimmability, and most importantly, its real life or the guarantee period. Be aware of the fact that false advertising galore due to the more complex nature of an LED light bulb. For example, if the application doesn’t require dimmability, why pay for the associated cost? Or why pay a lot of money for a light bulb that is not covered by a guarantee period of at least 3 years?

Parameter Minimum (Desirable)
Light Flux 700 lumens (1000 -2000 lumens)
Power Factor .90 (>.95)
Power Converter Efficiency .90 (>.95)
Light Cone <120-degree (30-60 degrees)
Life 20,000 hours (>50,000 hours)
Guarantee Period 3 years (5 years)


Q. I saw LED bulbs advertised as containing hundreds of high-brightness LEDs yet priced attractively. What’s the catch?
A. You get what you pay for. The hundreds of LEDs in the bulb are rated for a relative short life such as 10,000 hours. It is obvious that the higher the number of LEDs used in a bulb, the higher chance of failure. One LED failure and the bulb is to be recycled away. Furthermore, in spites of their high LED count, their light output rarely exceeds 200 lumens, which is good for a night light but not for reading or room illumination. A $1 incandescent 60-watt light bulb typically produces 750 lumens or less. Proper illumination of a room typically requires more than one 60-watt light bulb, often 2 to 10 of them, depending on room size and the purpose: intimate dining? Reading?

Q. What is Power Factor (PF)?
A. PF is a non-dimensional number quantifying how similar to a resistor, not how efficiently, an electrical equipment is using AC (alternative current) power made available to it via power lines. An incandescent light bulb for example has a PF of 1 but lowest energy efficiency. Most personal computers have a PF around 0.65, because the current flowing into them is highly distorted away from the ideal sinusoidal the power company would like to see. A PF of 1 minimizes power distribution losses. A PF of 0.50 will quadruple power distribution losses (Ohm’s law P = RI2). That’s why PearlLED designs its LED light bulbs for a PF higher than 0.95, to help you save energy and reduce your carbon footprint.

Q. What does high power converter efficiency mean to the user?
A. A good LED bulb typically contains a power converter driving series-connected LEDs with a DC current. A power converter efficiency of 100% means no electrical loss. An efficiency of 85% means an extra amount of 18% of total input energy is used up by the electronics to drive the LEDs with the same current. That 18% extra power is wasted as heat. PearlLED electronics is virtually lossless therefore it runs cooler!

Q. What is Color Rendering Index?
A. Color Rendering Index (CRI) is a number smaller than 100 indicating how close the light spectrum of a luminaire approaches sunlight or black body radiation. Fluorescent lights’ typical CRI is between 50 to 75. It is very difficult for CRI of LED luminaire to approach 100. A CRI greater than 90 is considered very good.

Q. What is Color Correlated Temperature?
A. CCT is a number expressed in Kevin degrees indicating whether the light color is warm (low CCT) or cool (high CCT) and anything in between. Some people prefer warm light colors, jewelry stores typically prefer cool light color. In spites of its name, CCT has nothing to do with actual temperature of the LEDs. Only what kind of color they emit.

Q. What is optical lighting efficacy?
A. It’s a ratio between useful light flux received and total light flux output of a lamp. An incandescent or fluorescent light bulb radiates light all around. In most indoor applications a shade is used to reduce or block beams from the bulb that hit directly our eyes, in other words to reduce glare or undesired light beams. Likewise, most ceiling-mounted fluorescent light fixtures have a reflector to reflect some of the light beams that otherwise go to the ceiling and lost, and for more expensive lighting fixtures, a parabolic louver to block however imperfectly glare. Parabolic louvers found in conference rooms, high-end business lobbies and offices are very expensive, often cost up to two orders of magnitude higher than the cost of the fluorescent tubes, yet their optical lighting efficacy is still lower than 50%. PearlLED™ bulbs are designed with high-efficiency optics that give you the highest possible lighting efficacy and none of the glare.

Q. What is glare anyway?
A. You need light to see objects around you but you don’t want high-intensity light to hit your eyes directly from a luminaire. During night driving, you’ve been bothered by those bluish high-intensity headlights of the more expensive cars from the opposite direction, preventing you to see the road surface and possible obstacles. That is due to glare from those headlights. Their owner can clearly see the road but the glare from their headlights prevents you from seeing yours. Recessed lamps are used in high-end business lobbies to let you see where you’re going but you don’t see the high-brightness light bulbs. Thus recessed lamps although much more expensive than a simple light bulb are chosen for their no-glare property. Likewise, anti-glare measures are adopted in conference rooms or meeting rooms to allow you to see the speakers and the presentation but not the direct light from the luminaire. PearlLED bulbs are designed with proprietary optics to have no glare.

Q. How much money do I save per year by switching to LED bulbs?
A. There’re four types of savings: energy cost, labor cost, air-conditioning cost, and replacement bulb cost. A PAR-30 bulb used in a business setting typically runs 10 hours a day, 360 days a year, or 3600 hours a year. An incandescent bulb lasts about 1000 hours thus needs 3.6 replacements a year, requiring manual labor to get new light bulb and to replace the dead one. At a marginal rate of electricity of $0.20/kWh, switching to LED bulbs saves about $120 a year in energy, labor and bulb cost, plus the cost of energy for cooling the heat generated by incandescent bulbs during warm months. Observe that most buildings and conference rooms have air conditioning running in the afternoons, due to heat from electrical equipment and from body heat of occupants. Yes, PearlLED light bulbs are much more expensive than incandescent light bulbs but they actually put money in your pocket years after years for some 15 years. The value of their energy savings over their very long life is in excess of $1500-2500 per bulb, depending on the power rating of the incandescent bulb they replace. A PearlLED bulb is actually a guaranteed 15-year annuity that pays about 100% a year! Switching to PearlLED bulbs is the best financial investment you can ever make, on top of reducing your carbon footprint and helping to stop adding more toxic mercury into the environment.

Q. What is the definition of marginal cost of electricity?
A. Users are charged by the utility company a higher rate once they exceed the base line, then higher again once they exceed the second threshold. Most Americans use more electricity than the base line, which is only about $30 a month. The top marginal rate can exceed $0.25/kWh in many states, such as $0.33 in Hawaii. The cost of electricity peaks during hot summer afternoons, where the utility companies have to operate their high-cost gas-fired power plants to supply the peak loads.

Q. What about toxic chemical such as mercury found in CFL?
A. LED contains no mercury and lasts up to 20X longer. Thus LED bulbs are very environment-friendly.

Q. Do you have a recycling program for dead bulbs?
A. After their long 15-year life, you can return dead ones for recycling and actually get some credit toward the replacement bulbs from PearlLED. PearlLED recycles 95% in weight of raw materials used in its production as part of its sustainability program.