Lighting Proposal: Replacement of Existing T-8 FL Tube
ƒÜ To replace existing T-8 (Fluorescent) FL
light tubes with more energy saving lights.
2. Design Criteria
l Achieve one-to-one replacement with minimum
alteration to existing light arrangement.
l Maximize energy saving and be as environmental
friendly as possible.
l Cost effectiveness.
3. Possible Alternatives to Replace the Existing
T-8 FL Tubes
There are a number of different types of light
sources available on the market today, namely incandescent lights,
Fluorescent/Compact Fluorescent (CFL) tubes/bulbs, Halogen/Metal Halide lamps
and LED (Light Emitting Diode) lights. Upon initial examination, incandescent
lights and halogen/metal halide lamps were eliminated for their higher energy
consumption and spot lighting characteristics. CFL tubes were also not
considered for it incompatibility to fit with the existing T-8 FL light
fixtures. In order to switch over to CFL tubes, all the light trays and fixtures
would have to be replaced which would mean a substantial increase in capital
investment. LED light is a fast developing technology, but is still quite
expensive. As a result, LED light is not a feasible option at this moment. The
remaining choices for further consideration would be the energy efficient T-5 FL
4. T-5 FL Tubes
T-8 and T-5 FL tubes on the market today have
the typical performance and technical specifications as stated in Table 2 below:
Table 1: T-8 vs. T-5 FL Tube Technical
In terms of energy consumption, a 1200mm T-5 FL tube uses
about 33% less energy than a T-8 FL tube, but due to the lower voltage output, a
T-5 FL tube would also generate less light than a T-8 FL tube. For example, if a
T-8 FL tube is replaced with a T-5 FL tube under a control situation where
condition remains the same; there should be a theoretical decrease in brightness
of about 20-30%. This calculation could easily be verified on by simply
measuring the Lux levels at a specified distance.
4.1 Special T-5 FL Tube Converter with Reflector
With the addition of the special light enhancing
reflector, the normally waste light of about 30% beaming towards the backside of
the light tray is reflected back downwards thus becoming useful light again. The
total useful light from a T-5 tube beaming downward would effectively be equal
to the light from a T-8 light tube. In other word, this combination of T-5 light
tube with reflector could achieve the 33% energy saving whilst matching the
brightness performance of a T-8 light tube, i.e. one-to-one replacement.
By achieving one-to-one replacement, there would be not
need to add additional light tubes or trays in order to compensate the decrease
in brightness level. Alteration or additional works to the existing lighting
arrangement could therefore be minimized.
4.2 Cost Savings Analysis
The monthly electrical costs of operating T-8 vs. T-5 FL
tubes for 11 hours/day are calculated as follows:
HK Electric (HK Island)
T-8 = (36W + 15W) x 11 hr x 30 days x $1.3/kwh / 1000W =
T-5 = (28W + 1W) x 11 hr x 30 days x $1.3/kwh /1000W =
Savings = $ 9.5
CLP (Kowloon, N.T. and Outlaying Islands)
T-8 = (36W + 15W) x 11 hr x 30 days x $1.0/kwh / 1000W =
T-5 = (28W + 1W) x 11 hr x 30 days x $1.0/kwh /1000W = $
Savings = $ 7.3
Assuming a difference of $100 capital cost (cost of
converter/reflector unit discounting the cost of the T-5 tube), the calculated
return periods are 10.5 months and 13 months respectively.
The T-5 FL tube converter with
reflector unit sold by our company has a factory warranty of 2 years against
manufacturer defect, but excluding installation workmanship, normal
wear-and-tear, or abuse.
4.4 Product and Project Photographs
T-5 Converter/Reflector Unit
Installed T-5 Converter/Reflector units at a typical office setting