Lumens are the measure of the absolute amount of light a
bulb provides. An integrating sphere is one measuring tool that’s used. It
first captures the bulb’s total light output in all directions across all the
different wavelengths of light. Then it weights the resulting values to reflect
the human eye’s sensitivity to each wavelength, summing up all the weighted
values to give an overall measure of “useful” light output. Dim bulbs may only
deliver 200 lumens or so, while really bright ones can deliver 2,500 lumens or
more.
Efficiency. If one lighting technology can deliver more
lumens of light per watt of power consumed, it is said to be more energy
efficient. Lumens per watt is the figure of merit for efficiency, but that
almost never appears on product labeling or packaging, so you have to calculate
it from the values that are provided separately. For example, say a standard 60
W incandescent is rated at 750 lumens—that’s 12.5 lumens per watt. Compare this
to a 14 W compact fluorescent rated at 900 lumens—that’s 64.3 lumens per watt.
Efficiencies can range from as little as 5 to more than 100 lumens per watt,
depending on the technology you choose and the amount of light you need.
Lifetime is now reported in years on product labels and
assumes three hours of operation per day (a little higher than typical usage
according to utility studies). Also, remember that the difference between a
projected lifetime of 20 years and 25 years on two products is probably not
meaningful, given the uncertainties in the accelerated lifetime testing process
and the degree to which new lighting products will continue to improve between
now and then. From a practical standpoint, the warranty a manufacturer offers
is more useful; the highest-quality products usually offer a 10-year warranty.
Color rendering index (CRI) tells you how accurately a bulb
renders a particular subset of colors (primarily pastels). A CRI of 80 or
greater is usually recommended by lighting experts, but there is debate in the
lighting community about the merits of paying extra money for products with a
CRI greater than 90—most users can’t tell the difference under typical
household lighting conditions.
Correlated color temperature (CCT;
reported in Kelvin, K) tells you how “warm” or “cool” the light from a bulb
appears. Residential users typically favor warm (approximately 2,700 K)
CCTs similar to incandescent bulbs, or 3,000 K (similar to halogen bulbs). In
the 4,000 K to 6,000 K range, the resulting light can appear bluish. It is
common for people who live in very sunny and tropical locations to favor bulbs with
higher CCTs, given their greater similarity to daylight or midday sunshine.
The Energy Star label appears on energy-efficient products
that deliver good performance in most of the attributes listed above. But
thousands of models now qualify for it, so you need to be more selective to
find the best performers. Also, be aware that many new energy-saving lighting
products are introduced to market a few months before they have completed
enough accelerated lifetime testing to earn the Energy Star label. The manufacturer
will later change the packaging to reflect receipt of that certification, but
the product inside the package can often be the same as the one selling a few
months earlier without the logo. This means that the most recently
introduced models without an Energy Star logo can occasionally be more
efficient and affordable than older models that are labeled.
More specialized information can often be found on product packages or
manufacturer websites, including beam angle and center-beam candlepower for
reflector lamps, compatibility with common dimmers, etc. If you are buying a
large number of efficient bulbs, check online reviews to find products that
have been consistently popular with other users, or buy from a retailer that
will allow you to return the products for a refund if you are unhappy with
their performance. For more details visit our website allindiayellowpage.com
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