Did you know that the general lighting service (GLS) bulbs we use at home could increase the wattage consumption? A 40W bulb may consume 10 per cent more electricity than that marked on the bulb, quietly burning a hole in your pocket. To us, the name of any widely sold product means a quality product offered at the least or at a reasonable cost. So we go by brands, don’t we? But when we tested the samples, some big names revealed poor performance.

Brands tested

We tested 10 brands of 40W, 230V (pear shaped) bulbs and three brands of 40W, 250V (two mushroom and one pear shaped) bulbs. The brands were selected on the basis of a market survey done all over India. In the 230V category there were Philips Classictone Clear, Bajaj, Osram Classic Clear, Surya Super, New Cema Super, GE Crystal Clear, Crompton, Anchor, Laxman Sylvania and Wipro Safelite. In the 250V category, we tested Orient, Prakash Lites (both mushroom-shaped) and Diamond (pear-shaped). All the brands were ISI marked as the GLS lamps are covered under a mandatory certification.

As specified by the Bureau of Indian Standards (BIS), we tested 35 samples of each brand for marking and other parameters. Out of these, 25 samples were tested for initial lumen and initial wattage.

Life Test

When you buy a bulb, your main concern is how long it will last. Twenty samples of each brand were tested for life at the rated voltage. As specified in the Standards, the bulbs were kept switched on for 1250 hours. They were switched off twice every day for not less than 15 minutes. This test was conducted in two parts. The ratio of the lumen (light output) of a bulb at 750 + or – 25 hours for an individual lamp to the initial lumen (i.e. light output measured initially) should not be less than 85 per cent. This ratio of all the brands tested was above 85 per cent. In the second part, the test was continued up to 1250 hours, as per the Standard.

After 1250 hours, the average life of 20 bulbs should not be less than 960 hours. Wipro Safelite (941.04 hours) and Prakash Lites (776.37 hours) failed the life test as they could not meet the requirement for an average minimum life of 960 hours.

Though, according to the Standards, the life test of the bulbs have to be discontinued after 1250 hours, we let the bulbs burn as long as they could to ascertain the life span in terms of the total number of hours.

Laxman Sylvania gave the maximum total average life of 1337.65 hours, followed by Crompton with 1330.26 hours in the 230V category.

Light Output

We tested the light output or initial lumen of 25 samples of each brand. For 40W, 230V, the initial lumen should not be less than 385.95 of an individual lamp. For 40W 250V, it should not be less than 381.3. The initial light output of all 13 brands met the Standard.

The initial lumen was found to be the highest in GE Crystal Clear (454.55 av.) followed by New Cema Super (450.56 av.). In the 250V category, the initial lumen was found to be the highest in Diamond (476.82 av.) but it failed to meet the requirements of initial wattage as per the Standard.

Energy consumption

Besides the cost of purchase, the cost of energy consumption of 40W lamps is a matter of concern. We calculated the energy cost per year for all the brands tested by us. We considered the average wattage of each brand, use of four lamps for at least four hours per day throughout the year with the cost of energy as Rs 4/ kilowatt hour (unit).

The energy cost per year for using Diamond lamps is the highest (Rs 1032.75) while that for using Philips Classictone Clear and Bajaj was found to be the lowest (Rs 937.20 and Rs 937.67 respectively).

Light output after 1250 hours

Apart from lasting long, a bulb must give good quality light. We checked the light output of the brands whose bulbs were still burning after 1250 hours.

This test was devised by our laboratory and not specified in the Standard. The light output at 1250 hours of seven brands (Surya Super, GE Crystal Clear, Osram Classic Clear, Bajaj, New Cema Super, Crompton and Laxman Sylvania) that survived up to this test ranged between 89.47 and 92.75 per cent of the initial lumen. The lumen maintenance of Orient (not conforming to marking) at 1250 hrs was found to be 93.95 per cent (average). Among the conforming brands, the lumen maintenance was the highest in Crompton with 92.75 per cent average. The light output of Philips Classictone Clear and Anchor could not be measured as the samples of these brands stopped working before 1250 hours.

The consumption of electricity is one of the major concerns for use of any electrical product. The bulb which we use should not consume more electricity than it is rated for. The wattage consumed by a 40W bulb should not be more than 42.1W. As per the Standard, 25 samples are to be tested and the number of bulbs whose wattage is above the maximum value should not exceed four.

We found Diamond (manufactured April 2005) defaulting. It consumed 44.21W on an average of the 25 bulbs tested as against the claim of 40W. The wattage consumption of Diamond ranged from 43.42 to 46.12.

This could be one reason why most of us are shocked to see our electricity bill, don’t you think?